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70th EAGE Conference and Exhibition incorporating SPE EUROPEC 2008
- Conference date: 09 Jun 2008 - 12 Jun 2008
- Location: Rome, Italy
- ISBN: 978-90-73781-53-5
- Published: 09 June 2008
1 - 100 of 556 results
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Thermochronological Evolution of the Northern Apennines
Authors M. L. Balestrieri and M. ZattinIn this work we show the results obtained with the apatite fission-track and (U-Th)/He methods applied on the Oligo-Miocene foredeep successions of the Northern Apennines. Results show that samples coming from west of the present drainage have been clearly totally reset for both thermochronological systems. Time of cooling below ca. 100°C is between about 10 and 3 Ma, with a slight decrease eastward. This decrease is more marked for cooling below 70°C, which vary from about 9 Ma to as young as 1 Ma. East of the drainage divide, fission-track and He systems are either partially reset or unreset. Here the amount of cover removed above the analyzed apatites was not sufficient to completely anneal fission tracks or to cause a total loss of He. Burial depths estimated from the data allow reconstructing the shape of the Ligurian Unit as a lid overriding the foredeep rocks until nearly the Adriatic Sea.
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Relation between Diagenetic Evolution and Tectonic Regimes in Thrust-fold Belt – The Calcari Grigi Group, Jurassic, Asiago Plateau, Northern Italy
Authors A. Ceriani, R. Di Cuia, A. Scifoni and A. RivaDolomitization and dolomite cements precipitation in Jurassic platform carbonates has been studied from outcrop samples of the Calcari Grigi Group (eastern Southern Alps, northern Italy). In the studied area various types of dolomites can be described at all scales of observation. On outcrops, primary dolomite can be recognised only in some stratigraphic intervals. By contrast, pervasive replacive dolomites are widespread throughout the area, mostly confined in the central and lower part of the sequence. The collected data demonstrate that the massive dolomite replacement was followed by a multiphase precipitation of dolomite and late calcite cements. The replacement occurred during burial, into a passive margin regime, due to compaction driven flow of formational fluids. Conversely, fluid inclusions data crossed with thermal history prove that dolomite and calcite cements precipitated when the study area was involved in collisional tectonics. Fluid inclusions data display a decreasing salinity trend from sea water to freshwater fluids. This observed dilution of fluids can be related to the infiltration of meteoric waters from the emerging Alpine chain. These data proof useful to interpret the diagenetic evolution of the unit as related to the evolution of the hydrogeological system in relation with the tectonic regime of the area.
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Thermo-kinematic Modelling and Organic Matter Maturity Analysis of the Alpine Rifting in the Southern Alps, N. Italy
Authors D. Scrocca, E. Carminati, D. Cavazza and C. DoglioniIn this paper we demonstrated how thermo-kinematic models and organic matter maturity data can be integrated to unravel the evolution of continental rifts. In particular we apply this model to an E-W 400 km long transect that cuts across the whole Southern Alps in northern Italy (Fig. 1). This profile, published by Fantoni and Scotti (2003), provides a valuable picture of the Mesozoic passive continental margin of the Adriatic plate at the end of Lower Cretaceous time (Aptian pp.). It is largely based, in its western and central part (about 250 km extending from the Biellese area to the Trento Plateau), on the palinspastic reconstruction proposed by Bertotti et al.(1993). Further east, this profile has been extended by Fantoni and Scotti (2003) to include the Belluno Basin and the Julian Plateau (Sarti et al., 1993).
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Thermal Modelling of the Extensional Mesozoic Succession of the Southern Alps and Implications for Oil Exploration in the Po Plain Foredeep
Authors P. Scotti and R. FantoriIn order to reconstruct the thermal history, organic matter maturity data were obtained from samples collected from sedimentary units outcropping in the Southern Alps. Resulting heat flow values are quite high and relatively uniform in the whole of the Southern Alps during Norian-Liassic; it progressively decreased after the Bathonian to reach values similar to the present ones at the end of the Cretaceous. This reconstruction is consistent with the known tectonic evolution of the Mesozoic extension in the Southern Alps, characterised by a rifting stage up to the Lias followed by a drifting stage from the Middle Jurassic. This kind of thermal regime evolution has strong implications for hydrocarbon exploration in the Po Plain.
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Thermal Conductivity of Sedimentary Rocks and Appropriate Corrections for In-situ Conditions
Authors V. Pasquale, G. Gola, P. Chiozzi, A. Frixa and E. VitaglianoWe attempt to remedy the existing deficiency of thermal conductivity data of sedimentary rocks by making a series of measurements in laboratory on several bottom core samples, collected from petroleum explorative wells and representative of the main sedimentary rocks recognized in the western Po Basin, Northern Italy. The in-situ bulk thermal conductivity is then estimated using calibrated formulas taking into account the mineralogical composition, the porosity and the effect of temperature.
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Automated Thermotectonostratigraphic Reconstruction of Sedimentary Basins in Frontier Areas
Authors L. H. Rupke, Y. Y. Podladchikov and D. W. SchmidWe demonstrate that automated reconstruction of the thermal, tectonic, and stratigraphic evolution of sedimentary basins is possible and fast. We achieve this by coupling a numerical forward model with an optimization module. The numerical model allows for self consistent implementation of virtually unlimited physical processes. The optimization module modifies the parameters of the forward model iteratively until a best fit satisfying the constraints is found. The package is tested with the benchmark case study of the Viking Graben, North Sea. The petroleum system of the Viking Graben is well studied and allows for detailed comparison of the model results. In particular, we show that the predicted hydrocarbon maturity corresponds well to actual production fields. The possibility to implement additional physics is exploited in the presented case with mantle phase transitions activated. These density changes are known to occur in the mantle but are not implemented in other models. In essence the effect of phase transitions is to amplify the effect of thinning and perturbing the thermal field, leading to smaller (depth dependent) stretching factors compared to cases with phase transitions deactivated. This leads to smaller heat input and consequently a relatively cooler evolution of sedimentary basins.
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Diagenetic Evolution and Distribution of Dolomite Bodies in a Partially Dolomitised Sequence - The Calcari Grigi Group
Authors R. Di Cuia, A. Scifoni, A. Riva, A. Moretti and A. CerianiA multidisciplinary study conducted over the carbonate platform deposits of the liassic Calcari Grigi Group (Southern Alps), highlighted how the use of a 3D field analogues can contribute to better define the distribution of dolomitic bodies related to fault networks, to characterise the petrophysical properties of the dolomitic sequence and to unravel a complex diagenetic history. Pervasive unimodal and patchy polymodal dolomites characterize a thick portion of the Group, and are topped by a smoothly curved - not stratigraphic front. This latter tend to uprise near to the major faults and fracture swarms, with massive–chaotic dolomite. Associated to these zones there is the development of stacked high-porosity and permeability bedding-parallel bodies that show excellent petrophysical properties. Thin section, Cathodoluminescence, isotopic and fluid inclusions analyses were used to constrain the paragenetic evolution of the sequence. The result is a complex paragenetic evolution, in which good porosity developed but in later stages porosity was reduced by the deposition of calcite and dolomite cements. Fluid inclusions results relate the evolution to a complex interplay between fluid evolution, tectonics, burial and hydrological processes, while isotopic analysis suggests a Miocene age as a timing for the late diagenetic stages.
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Insights on the Evolution of Oligocene-miocene Carbonate Buildups from 3D Seismic Data, East Java Basin, Indonesia (Best of AAPG)
Authors A. S. Ruf, T. Simo, T. M. Hughes and K. SteffenThe High Density MC3D seismic survey, acquired by PGS in 2003 over the North Madura platform, is an excellent data set for quantitative interpretation of carbonate mound evolution. Detailed imaging of the growth histories of Oligocene-Miocene carbonate buildups provides insight into geometric parameters characteristic of platform initiation, development, and demise. Mound initiation occurs with development of small (<100m to 500m diameter), closely spaced, domal buildups, which become the nuclei for the formation of intermediate mounds (2km to 3km diameter). Nucleation mounds build concentrically to form intermediate mounds, which selectively coalesce into amalgamated platforms (>5km diameter), become isolated platforms of varying size (<5km diameter), or die off altogether. The high quality seismic data enables visualization and quantitative analysis of geometry, orientation, and spatial distribution of nucleation and intermediate mounds, generating models of preferential morphology for development of isolated vs. amalgamated platforms. Flattened discontinuity time-slices from the 3D data provide clear images of mound size, distribution, and morphology at discrete growth steps, which record a complex history of initiation, aggradation, coalescence or isolation, progradation, potential exposure, and demise.
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Three-dimensional Seismic- and Sequence-stratigraphic Framework of a Lower Cretaceous, Aptian, Supergiant Carbonate Field in Onshore Abu Dhabi (Best of Shu'aiba)
Authors L. A. Yose, C. J. Strohmenger, A. S. Ruf, I. Al-Hosani, A. M. Gombos, G. Bloch, S. Al-Maskary and Y. S. Al-MehairiA three-dimensional (3-D) dataset over a carbonate field in onshore Abu Dhabi was evaluated to develop integrated sequence-stratigraphic and reservoir models for the Lower Cretaceous (Aptian) Shu’aiba Formation. The study area is positioned over the Shu’aiba platform-to-basin transition and provides a type area for linking the stratigraphic framework across the shelf, slope and basin environments (Yose et al., 2006). The more than 50 kilometer long shelf-to-basin transect records a diverse range of depositional facies and stratal geometries that have a large impact on reservoir quality and connectivity across the study area. The Aptian reservoir interval (Shu’aiba Formation) records a second-order supersequence that is divided into five (5) depositional sequences. Rudists, carbon and strontium isotopes and nanno-fossils provide internally consistent age constraints on Upper versus Lower Aptian sequences. The age dating also allows for tying sequences to the higher resolution Aptian (AP) chronostratigraphic zonation in Hardenbol (1998). Sequence 1 (Lower Aptian; possible AP-1 and AP-2 age) and Sequence 2 (Lower Aptian; dated as AP-3, lower part) were deposited during the transgressive phase of the supersequence. These sequences are retrogradational, record the initial formation of a low-relief ramp, and are dominated by algal-microbial facies. Ramp interior and margin facies of the transgressive phase are characterized by high porosity and low permeability due to mud-dominated textures and development of microporosity. Sequence 3 (Lower Aptian; dated as AP-3, upper part) was deposited during the highstand phase of the supersequence, is mainly aggradational, and records the proliferation or rudists across the platform top. Grain-dominated platform interior and margin facies of Sequence 3 are the highest quality reservoir facies within the Shu’aiba reservoir. Sequence 4 (Upper Aptian; dated as AP-4) and Sequence 5 (Upper Aptian; dated as AP-5), were deposited during the late highstand phase of the supersequence. These sequences are progradational and record the progressive downstepping (forced regression) of the platform margin onto a low-angle (1-2 degree) slope. Clinoforms of the late highstand phase are characterized by alternations of high (grainy) and low (muddy) reservoir quality developed in response to relative sea level changes. Sequence 6 (probable AP 6 time; Upper Aptian to Albian?) was deposited during the second-order lowstand, records the influx of fine-grained siliciclastics, and forms the base of the next overlying supersequence. Results from the study have led to an improved understanding of platform evolution and reservoir architecture. A new platform margin was recognized to the south, indicating the development of an intra-platform seaway. With margins now recognized to the north and south, it is possible that the Shu’aiba evolved into a series of isolated platforms during the transgressive to highstand phases in the Early Aptian. Some of these isolated platforms are interpreted to have coalesced via progradation as second-order sea level began to fall in the Late Aptian. The platform interior and margin facies show a marked asymmetry from north to south that are interpreted to be related to ocean currents or prevailing winds. These results provide new insights on reservoir quality and connectivity. In the platform interior area of Sequence 3, 3-D seismic data reveal a complex mosaic of tidal channels, high-energy rudist shoals, and inter-shoal ponds that impact reservoir sweep and conformance. At the basin margin, the seismic data provide high definition images of platform margin clinoforms that impact reservoir architecture and well-pair connectivity.
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Definition and Distribution of the Bab Sequence – The Last Upper Aptian Shu’aiba Sequence in the Bab Basin (Best of Shu'aiba)
The Shu’aiba Formation consists of six depositional sequences. The first five sequences make up a 2nd order supersequence, while the sixth sequence is the lowstand sequence of the next supersequence. The sequence is deposited within the Bab basin as a set of prograding clinoforms. This sequence is here called the Bab Sequence and is equivalent to the “ap6”, “sequence 6”, and the “Upper Shu’aiba sequence 3” of other authors. The sequence boundary at the base of the Bab sequence coincides with the supersequence boundary and is characterized by a major exposure across the Shu’aiba platforms and down-stepped deposition. The onset of clay deposition marks the beginning of the Bab Sequence. Internally the Bab Sequence consists of nine clinoforms (high-frequency sequences) that prograded into the Bab Basin in a series of clinoforms over more than 30km. The most striking observation is the extremely regular and seaward progression of the clinoforms, sub-linear along the southern margin and concentric around the eastern isolated platforms, resulting in a series of almost perfectly parallel clinoforms. The prograding clinoforms can be grouped into three sets. The 4 clinoforms in the first set are relatively wide, with mounded topsets at the margin. They reach a thickness of 120 meters. The top surface of these first clinoforms lies 30 to 40 meters below the top of the previous shelf break (sequence ap5). The 3 clinoforms of the second set are relatively narrow, reach 115 m in thickness and have a slightly steeper slope than the first set of clinoforms. The last two clinoforms (third set) are broader and thinner (75 meters in thickness) and have a very low angle slope. The almost perfect parallel geometry of clinoforms is likely the result of the regular distribution of clay and carbonate mud along the margins by long-shore currents. The lithologic content of the clinoforms varies within the three sets. The topsets of the first set of clinoforms tops are rudist-bearing wackestone – rudstone, the foresets are composed of burrowed argillaceous wackestone, and the bottomset of calcareous shale. In the topsets of the second set of clinoforms the rudist facies is missing and replaced by marl-limestone alternations with occasional skeletal packstone layers. The third set is dominated by clay and marl-limestone alternations. The rudist-bearing topsets form the main reservoirs in the Bab sequence, whereas the clay-rich intervals may provide seals for a stratigraphic play.
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Regional Depositional History and Stratigraphy of the Shu’aiba Formation in the Middle East (Best of Shu'aiba)
Authors H. Droste and B. J. PiersonThe carbonates of the Aptian Shu'aiba Formation form major oil reservoirs in the Middle East. The formation shows a complex internal stratigraphic architecture and significant lateral variations in reservoir character. During a 3-day workshop held in Oman, which was attended by Shu’aiba experts all over the world, a common understanding of the stratigraphic framework was reached, which led to a consistent regional model at the scale of the southern Arabian Plate. The Shu'aiba Formation represents a depositional cycle within a Cretaceous epeiric carbonate platform system. It is built by three composite sequence sets, each with different facies associations and internal stacking patterns and, consequently, also different reservoir architecture. The lowermost unit is early Aptian in age and includes the Hawar Member of the underlying Kharaib Formation and the basal Shu'aiba Formation. It forms a Transgressive Sequence Set with laterally extensive shallow-marine to intertidal sediments followed by shallow-marine algal limestones that transgressed over exposed limestones of the Kharaib Formation. The development of algal-mound complexes led to a differentiation on the platform. Between these mounds fine-grained, in places organic-rich, deeper-water deposits represent the maximum flooding interval. The second unit is early to late Aptian in age, and consists of a Highstand Sequence Set (HST) with progradational geometries. The "carbonate factory" was then dominated by rudist-biostrome complexes, which colonized the mounds. Intermound depressions were progressively filled leading to the formation of a large platform that surrounded an intra-platform basin. The third unit is formed by a Lowstand Sequence Set (LST) deposited in the late Aptian during and following a regional drop in sea level. The drop caused subaerial exposure of the HST platform and the influx of fine-grained clastics. The LST contains off-lapping wedges of argillaceous carbonates and carbonate-rich claystones along the margins of the intra-platform basin. Clays deposited during the following transgression provide a regional seal to the Shu'aiba reservoirs. The advantage of this sequence stratigraphic framework is that it can be used as a template which: 1) Explains the regional variation in reservoir/flow properties. 2) Allows grouping of fields according to stratigraphic setting for comparison / analogues in reservoir studies.
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Pore Geometry as an Indicator of Depositional Texture and Velocity Variations in Chalks
Authors M. R. Saberi, T. A. Johansen and R. AgersborgThe complex pore geometry in carbonates makes their velocity behavior difficult to predict. Integration of geology information can help to make a predictive pattern for pore geometry and as a result for velocity. In this paper, based on available diagenetic models for chalks, an integrated modeling strategy is developed for velocity variation in a mineralogically uniform chalk. It can be shown that different depositional texture in chalks can be expressed by different depositional pore aspect ratio. This depositional aspect ratio transforms to other aspect ratio by post-depositional processes. This transformation of pore aspect ratio in chalks can be predicted from geology information and mostly from foraminifer’s contents and sorting information of the sediment. Mechanical compaction and cementation although both decrease porosity with depth but may increase the velocity by different rates, since one makes more compliant pore throats while another one close cracks and makes stiffer pore bodies, respectively. These show the relevance of pore geometry consideration in velocity interpretation, since some variations in velocity data may results from pore geometry (depositional texture) and its transformation (post-depositional process) through different diagenetic environments rather than mineralogy, fluid or porosity.
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Fluid-escape Features Due to Silica Diagenesis in the Faeroe-Shetland Basin
Authors N. R. Goulty and R. J. DaviesConversion of opal-A to opal-CT in biosiliceous sediment during burial expels water expulsion by porosity reduction and dehydration. This release of water occurs over large tracts of sedimentary basins within discrete diagenetic reaction zones at burial depths in the range 200-800 m. Seismic data from the Faeroe-Shetland Basin provide evidence for a variety of fluid conduits which terminate upwards in roughly circular erosional depressions at an Early Pliocene unconformity, interpreted as the contemporaneous seabed. These features are indicative of water expulsion and focused fluid flow emanating from the opal-A to opal-CT reaction zone. The sediment immediately below the reaction zone contains, on average, ~30% opal-CT by weight. The estimated volumetric rate of water expulsion per unit surface area during the Quaternary has averaged ~6 m3 My-1 per square meter, which is greater than the vertical flux of water at the same depth from compaction of the deeper basin fill, and amounts to a volumetric rate of ~120 km3 My-1 across the whole basin. In late Miocene times, the calculated rate of water expulsion was around six times greater, which explains why the fluid-escape features terminate at the Early Pliocene unconformity.
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Shale Dependent Sediment Compaction - Is There a Global Porosity Relationship? Scanning of Parameters in Wells
Authors A. E. Lothe, Ø. Sylta, E. Fjær and H. M. HelsetA silisiclastic porosity compaction relationship has been derived for sedimentary basins, where shale volume contents (Vshale) from well logs are used as input. The relationship has been derived from simplified assumptions about stress-paths and rock compressibilities, in combinations with a published relation between mean grain size an sea-floor porosity and a relation between mean grain size content and clay content. The porosity-depth relationship has been tested on well data. Two input parameters may be optimized and result in a narrow range of low misfit values between observed and measured porosities.
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Subsurface Geometries in Central Sicily FTB as a Premise for Hydrocarbon Exploration
Authors R. Catalano, V. Gatti, G. Avellone, L. Basilone, A. Frixa, R. Ruspi and A. SulliThe study concerns a sector of the Maghrebian Sicilian Fold and Thrust Belt (FTB), located in central Sicily between the southern edge of the Madonie Mts. and the Caltanissetta trough. Interpretation of recently acquired seismic profiles, constrained by joint detailed stratigraphy and field investigation, revealed the structure of the study area as formed by a thick pile of deep water carbonate (Imerese and Sicanian) thrusts lying on carbonate platform imbricates. In the forward migration of the FTB, two main tectonic events were envisaged; shallow and deep seated thrusts occurred during the Miocene-early Pleistocene time interval that deformed the former sedimentary cover of the continental margin. The kinematic model and the occurrence, at depth, of carbonate platform rock bodies indicate the study area as a potential frontier for hydrocarbon opportunities.
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Overview of the Italy's Petroleum Systems and Related Oil and Gas Occurences
Authors F. Bertello, R. Fantoni and R. FranciosiItaly bears a big variety of petroleum systems. The hydrocarbon occurences can be classified as associated with three main tectono-stratigraphic systems: 1) biogenic gas in the terrigenous Plio-Quaternary foredeep wedges, 2) thermogenic gas in the thrusted terrigenous Tertiary foredeep wedges, and 3) oil and thermogenic gas in the carbonate Mesozoic substratum. The potential of the hydrocarbon reserves makes the country the most important hydrocarbon province of the southern Europe.
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Nuclear Magnetic Resonance and Data Integration in Murzuq Basin, Libya - Case Study
Authors J. Dessay, J. M. Gonzalez Muñoz, M. Sweed and A. BoitelRepsol Exploration Murzuq S.A. (REMSA) utilizes Nuclear Magnetic Resonance (NMR) data through two different procedures: - Qualitative interpretation tool: NMR porosity-permeability information is integrated and combined with the petrophysical formation evaluation, logging formation pressure data, core(s) evaluation (when available) and used to decide a possible well production test. - Part of Quality assessment: as part of the geological data management workflow, the NMR data is combined with the rest of wireline logging data, core informations and drilling & gas data for an integrated quality control.
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The Main Tectono-sedimentary Domains of the Pyrenees
Authors J. J. Biteau, J. Canerot, P. Mallard and G. NesenThis presentation covers extensively the whole area located between the Charentes, in France, to the North, and the Ebro Basin, in Spain, to the South. It aims to describe the main components of the very contrasted Petroleum systems (P.S.) that have been evidenced in this area, where there has been more than 60 years of hydrocarbon exploration and production
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Hydrocarbon Bitumen in Deepwater Gulf of Mexico - An Integrated Petroleum Systems and Engineering Perspective
Authors J. Huang, G. Han, K. Grush, N. McCormack and G. SulistyoHydrocarbon bitumen, here defined as a highly viscous hydrocarbon accumulation, has been encountered during the exploration and development of several deepwater discoveries in the Gulf of Mexico (GOM). These bitumen occurrences pose significant challenges to deepwater GOM drilling operations. Several field development projects experienced substantial increase in drilling costs associated with such bitumen encounters. Our study was aimed at a holistic understanding of subsurface bitumen behavior through a broad integration of both geoscience and engineering approaches. Petroleum systems analysis indicated that bitumen encountered in the greater Pony area is low-maturity kerogen derived from a mobilized source rock of Jurassic age. This bitumen was most-likely mobilized in early Miocene, prior to peak oil and gas generation. A series of rock mechanics tests revealed that bitumen mechanical and flow properties are primarily controlled by temperature and conditions of confining stress. The highly viscous nature of subsurface bitumen at source level forces the bitumen migration and emplacement process to utilize sediment interfaces such as fractures, faults, and salt welds, rather than Darcy flow through porous media. These multidisciplinary findings provide important constraints to bitumen emplacement timing, spatial distribution and geometry which, in turn, have direct implications for mitigation strategies in drilling operations.
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Tectonic Heat Flow Models - Workflow and Cases
Authors H. J. M. Verweij, J. D. Van Wees, D. Bonte, P. David and R. Abdul-FattahTo obtain a pragmatic workflow solution for tectonic heat flow prediction, we have developed in the recent years a multi-1D probabilistic tectonic heat flow model, which is capable of calculating tectonic heat flows, incorporating a variety of tectonic scenarios (including rifting, underplating, mantle upwelling). The model has been applied for a range of basin settings. For (frontier) deep water basins in the Caribbean and Mediterranean regions, we show that basin maturation is significantly higher and occuring much earlier when adopting tectonic heat flow instead of a constant heat flow. For mature basins such as in the Netherlands, we show that tectonic heat flow scenarios considerably aid in identifying and understanding of unexplored play systems, by putting temporal and spatial constraints on paleo heat flow. In particular modelling results indicate that the interplay of rifting, underplating and foreland formation and inversion, has resulted in much stronger temporal and spatial tectonic heat flow variations than hithertoo assumed.
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Exploring in the Utah Hinge Line Using a Multi-disciplinary Approach
Authors J. Barraud, D. Bate, M. Davies, P. Houghton and P. VersnelMountainous Thrust Belt areas are typically challenging settings for oil and gas exploration. The topography and geologic complexity combine such that land based geophysical data acquisition is expensive and may leave many questions unanswered. However, the pay back from successful exploration can be large. One such successful example is the discovery of Covenant Field by Wolverine Gas and Oil, in the Utah Thrust Belt, USA in 2003. ARKeX in association with JEBCO Seismic have acquired 150 sq mi of BlueQube data, centered on the Covenant Field discovery. The objective of this work was to identify the BlueQube response of a known anticlinal structure in the thrust belt trend. With an understanding of the response from this known field, the BlueQube data is being used to develop an exploration strategy along the Thrust Belt.
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De Ruyter Field, Netherlands - Discovery and Near-field Exploration
Authors F. Blom, L. van Borren and M. BaconDe Ruyter field is located in the southern North Sea on the Dutch Continental Shelf. The discovery well was drilled in 1996 on a seismic anomaly and the well found gas with an oil rim in sandstones of Triassic age. An appraisal well drilled in 1997 on an adjacent compartment found oil without a gas cap in Permian sandstones. Subsequent exploration drilling in the area proved unsuccessful. Recently however, seismic amplitude interpretation has identified a number of prospects with a high chance of containing hydrocarbons. Two of these prospects were drilled during 2007 and both wells discovered gas. The current approach to exploration in the area is focused on validation of seismic anomalies and is aimed at de-risking drillable prospects. This paper demonstrates how validation is based on a rock physics model and observations on seismic amplitudes and flat events.
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Reservoir Characterization and Palaeo-environmental Reconstructions of Upper Carboniferous Strata in the Cleaver Bank High Area
Authors O. A. Abbink and T. B. Van HoofRecently, renewed interest in the hydrocarbon potential of Upper Carboniferous strata of the North Sea basin (and especially the Cleaver bank High area) led to an increased exploration activity in this area of the Dutch and UK offshore. The Upper Carboniferous deposits in the Cleaver Bank High area are characterized by a high lateral variability in sedimentological facies which makes prospecting for hydrocarbons difficult. Therefore, a high resolution stratigraphical framework in combination with a better insight in the distribution of sedimentological facies is needed to increase the exploration efficiency in this area. This is achieved by high resolution quantitative palynology on ten wells from the Cleaver Bank High area (Dutch offshore).
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An Evaluation of the Petroleum System - Offshore Morondava Basin, Madagascar, Based on 2D Seismic Data Interpretation
Authors M. S. Tamannai, D. Winstone, I. Deighton and P. ConnThis study addresses the regional interpretation of 2D seismic data acquired in 2003 and 2005-2006 by TGS-NOPEC integrated with satellite gravity data and source rocks modelling to analyze the petroleum system of the offshore part of the Morondava Basin (Madagascar). Seismic and satellite gravity data interpretation suggests that the western coastal basins of Madagascar can be split into two tectonic provinces i.e a western passive margin and an eastern failed rift. The structure, depositional environments and burial histories of these two provinces are quite distinct. Hence, the potential petroleum systems that occur in each province are also different. The offshore part of the basin is under-explored but found to be highly prospective. Evidences of direct hydrocarbon indicators have also been found. The burial and hydrocarbon expulsion histories for source rocks of Permo-Triassic and Mid Jurassic ages were modelled and encouraging results have been seen. The structuration happened before the oil expulsion from these source rocks which maximize the chances of finding hydrocarbons in place. Potential good quality reservoirs including predominantly sandstones and limestones have been interpreted which are covered by interbedded seals. Hence, all elements of an effective petroleum system were identified during this study.
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HC Bearing Area in the Eastern Part of the Ukrainian Black Sea
Authors S. N. Stovba, O. I. Khriachtchevskaia and I. V. PopadyukA regional investigation of the eastern part of the Ukrainian Black Sea has been carried using a vast set of regional seismic reflection profiles, including the new set of regional seismic profiles by Naftogaz of Ukraine. The drilling of Subbotina well 403 in 2006 has confirmed the huge oil and gas potential of the Kerch shelf. The recoverable reserves of the field are expected of more than 100 ml. tons of oil and 100 bln. m3 of gas. 20 large structures with closures of 50-200 km2 within the Kerch shelf have been mapped within Oligocene-Miocene-Pliocene sediments. The structure and growth history of the prospects and Subbotina structure are the same. Some of the prospects have much more size than Subbotina structure. A number of high-amplitude anticlines has been mapped and a huge Mesozoic structure of 400 sq. km in deep water depth up to 2200 m. There are strong direct hydrocarbon indicators on seismic data. According to expert appraisal, every major lead formed within the Upper Mesozoic-Cenozoic section in water depths of 100 m to 2000 m has an area of several hundred sq. km, with vertical closure of hundreds of meters, and has the potential to contain hundred million barrels of recoverable hydrocarbons.
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Digital Point Receiver Seismic Acquisition and Pre-stack Reservoir Characterization at Sulige Gas Field, China
Authors M. C. Li, S. Q. Shi, Y. B. Du, Z. H. Yao, D. X. Wang, M. B. Zhang and S. J. ChengSulige gas field (Ordos basin, Inner Mongolia) is the largest onshore gas field in China with proven gas reserves of 1.1 trillion cubic meters. This thin multi-layered deltaic reservoir of lower Permian age is very heterogeneous which prevents development drilling from high success rate (less than 60%). With respect to these characteristics and to the depth of the reservoir (3000 m), an improvement in surface seismic was mandatory more efficiently detect the sweet spots. This has been accomplished using point source - point receiver dense 2D acquisition based on explosive and digital 1C MEMS accelerometers. Data processing as well was revisited to better preserve amplitude of the CDP gathers used as input of pre-stack inversion and AVO analysis. Digital sensors proved to be more effective in preserving far offset amplitude than the conventional arrays of geophones. The resulting lithological and gas content predictions, confirmed by 30 new wells, demonstrate their effectiveness in delineating sweet spots. Success have improved by 50% and Sulige gas field has now tripled its natural gas output capacity, helping PetroChina to meet surging domestic energy demand: the field’s annual capacity reached 4 billion cubic meters by end 2007 from 1.3 billion the previous year.
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Effect of Zechstein Supergroup (Z1 Cycle) Werrahalit Pods on Prospectivity in the Southern North Sea
Authors J. R. Underhill and K. L. HunterResults of a seismic interpretation and the analysis of exploration wells in license blocks in the southern part of Southern North Sea (SNS) Quadrant 49 highlight the presence of poorly documented, lensoid Werrahalit pods within the lowermost of the Upper Permian, Zechstein Supergroup (Z1) carbonate-evaporite cycles. Their occurrence has a demonstrable effect on the accurate definition of structural traps and reserve estimates in the highly prospective Leman Sandstone Formation reservoir underneath. There remains a clear need for the zone in which the pods occur to be delimited and the effect of the Werrahalit to be accounted for when evaluating remaining prospectivity in the SNS in order to assess the exploration and production risks and rewards that their presence brings.
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Complex Fractured Carbonate Reservoir Potentials - The Impact of Dettailed Structural Analysis - The Example of the Maiella
Authors R. Di Cuia, D. Casabianca, A. Shakerley and M. MasiniThe carbonates of the Maiella Mountain (Italian Apennines) was studied to verify the consistency between forward model predictions and field measurements in a carbonate fracture sequence. The variability of depositional environments and facies, with the depositional trends orthogonal to the main present day structural axis, makes the Maiella Mountain an ideal outcrop for studying how carbonate units located in contrasting depositional environments (different textures and organization but similar structural locations) react to stress and develop fracture networks. This study was undertaken with a multidisciplinary approach and focused on the detailed acquisition and analysis of outcrop data (fracture, and facies) from sequences located in different depositional environments and structural settings. The results of the fieldwork were then compared with the fracture systems predicted by a forward modeling technique applied by restoring seismic-scale cross sections. The comparison highlights that : a) the structural model predicts correctly fracture density distribution at the field scale (km’s); b) the structural model does not fit fracture density data at the inter well-scale (100’m); c) the number of fracture sets predicted by the model is not consistent with observed data; d) fracture connectivity is higher in the field than that proposed by the model.
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Structural and Sedimentological Evolution of the Ultra-deep Gas Play Fairway - Gulf of Mexico Shelf, Texas and Louisiana (Best of AAPG)
Authors C. L. Farmer, D. H. Phillips, R. H. Benthien, D. V. Dailey, B. W. Horn and D. G. DerbeckerUltra-deep drilling activity on the Gulf of Mexico shelf is targeting a new deep gas play fairway below established older production. The fairway extends from the Mississippi delta across the Texas shelf in the section below 25,000 feet. Large relatively simple anticlines with inverted Paleogene and Cretaceous sediment packages have been identified. These packages have been mapped regionally and locally to identify isopach thicks that should be favorable for accumulation of reservoir sandstone. The main exploration risks identified for the ultra-deep fairway are reservoir presence and quality. The targeted deep structures contain sediments that exhibit internal ponded geometries with thickening axes coincident with present day anticlinal axes. Closure on many of the deep inversion anticlines formed very early as a result of initial autochthonous salt withdrawal. The deep structures are de-coupled from the shallower growth faulted section. Restoration of the structures through geological time indicates a complex interaction between salt thickness, depositional thickening and structural geometry.
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The Influence of Tectonics on Temporal and Spatial Variations in Sandbody Architecture – Cretaceous Gosau Basin, Western Calcareous Alp, Austria (Best of AAPG)
Authors D. Paton, M. Carr, H. Ortner, R. Amerman, J. Borer, P. Plink-Bjorklund, D. R. Pyles, B. Trudgill and R. J. WildThe Cretaceous Gosau deep water basin, western Austria, provides an exceptional example of syn-depositional structural influence on sandbody architecture. Significant variations in sandbody architecture are observed in both proximal to distal and axis to margin settings; these can be attributed to the basin's structural configuration. The west of the basin (proximal) is structurally confined and characterized by amalgamated coarse-grained channels. In contrast, structural deformation increases towards the east (distal) generating significantly greater accommodation space that results in both a deepening of the basin and an increase in basin width (from ~ 0.5 to 3 km). There is a corresponding change in strata to repetitive couplets of high-aspect ratio lobeform conglomeratic Mass Transport Complexes (MTCs) overlain by thinly bedded turbidites. The axis to margin variation is most pronounced in the medial portion of the basin where superb exposure of progressive rotation of strata is associated with structural growth of the basin margin fold. Immediately adjacent to the growth fold the basin fill is dominated by re-mobilized coarse grained facies and MTCs (~ 90 % of gross stratigraphy). Coeval strata in the axis are more finely bedded turbidites (coarser grained facies ~ 30 % of gross stratigraphy).
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Outcrop Characterisation of Turbidite Reservoir Analogues Deformed by Fluidisation - Implications for Reservoir Models
Authors A. Scott, O. Stanzione, A. Hurst, M. Vigorito, J. Moreau, W. Vettel and J. CartwrighThe study of post-depositional sand remobilisation and injection processes has become increasingly important in the oil and gas industry because of the considerable impact on reservoirs quality. Nevertheless, the effect of remobilisation of large volume of sand through fluidisation processes on turbidite reservoirs is still poorly understood. This creates significant issues for reservoir modelling, reserve estimation, well planning and drilling. Outcrop analogues provide essential inputs for the reservoirs modelling by constraining the geometry and petrophysical properties of modified sandbodies. The Panoche Giant Injection Complex (PGIC, Panoche-Tumey Hills, California, USA) is the largest injection complex yet documented from outcrop. This injection complex covers an extended outcrop area and crosscut about 1200 m of slope mud-rich succession with a complex system of dykes and sills. The injections are sourced from isolated slope channels, channel complexes and lobes which provide exceptionally well exposed analogues for turbidite reservoirs modified by fluidisation and injection. We describe such modifications in terms of external geometries, internal architecture and facies distribution and provide examples of how these modifications affect the reservoir properties and the distribution of porosity and permeability.
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Application of Structural Analogs to Enhance Understanding of Tectonically Inverted Settings (Best of AAPG)
Authors D. J. Reynolds and J. R. UnderhillIntegration of field and subsurface data from the Wessex Basin (UK) and Doseo Basin (Chad) has provided important new insights into petroleum prospectivity in structurally inverted settings. Using these data it has proved possible to refine models of inversion anticline development and recognition criteria for a variety of polyphase deformation scenarios. In the Wessex Basin, structures are exposed that are typically difficult to image seismically, such as the steeply dipping, highly deformed forelimb of inversion anticlines. These regions are particularly important to resolve when mapping trap geometry, field extent, and fault displacement for fault seal analyses. In all cases the inversion anticlines are related one-for-one with early rift faults, regardless of their trend and that relaying normal faults produce en-echelon inversion anticlines. Thus, en-echelon folds do not indicate strike-slip faulting a priori. In addition, maximum inversion is coincident with the center of the fault segment where maximum subsidence occurs during extension. As a result, much can be interpreted about the pre-inversion structure by mapping the inversion anticlines themselves.
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How Do Relay Ramps Influence Sedimentation in Rift Settings? A Study Combining Sandbox and Numerical Experiments
Authors W. Athmer, R. M. Groenenberg, S. M. Luthi, M. E. Donselaar, D. Sokoutis and E. WillingshoferIn this experimental study the influence of relay ramps on submarine fan deposition is investigated by combining physical laboratory experiments with fluid flow computations. The laboratory experiments comprised a two-layer sandbox model with sand and silicone put under extensional stresses to produce a rift basin with relay ramps. Its laser-scanned topography served as digital elevation model for the FanBuilder program, in which turbidity currents were modelled under different inflow directions to the rift axis. The relay ramps were found to behave as pathway for the flow if the angle of incident was small compared to the ramp incline. Wide and antithetic relay ramps with small dips can thus function as depocentres. Narrow ramps are by-passed, and the turbidity currents flow down the main gradient of the rift edge to form basin floor deposits. In order to simulate syn-tectonic sedimentation the deposits obtained from the numerical calculation were physically added to the sandbox model before and during resumed extension. Serial cuts in the analogue model after the experiments exhibited the internal structure of the modelled rift basin.
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3D Geological and Seismic Forward Modeling of a Sinuous Slope Channel Complex, Brushy Canyon Formation, West Texas (Best of AAPG)
Authors M. Tomasso, D. R. Pyles, F. L. Bonnaffé and D. C. JennetteSeismic interpretation reflects some aspects of the sub-surface geology, but the scaling of seismic images rarely shows the full geological picture. Many stratigraphic architectural elements are typically at higher resolution than the acquired seismic image, and their interpretability on seismic profiles is often limited. The ability to directly compare outcrops with seismic objects has the potential to bridge this scale-gap. Seismic forward modeling of outcrops enables the examination of known stratigraphy and depositional elements at various scales. We discuss the construction of a fully three-dimensional geologic model, based upon the Beacon Channel outcrop of the Brushy Canyon Formation of west Texas, which is interpreted as a sinuous slope channel complex. A high-resolution 3D digital outcrop dataset was acquired using a ground-based lidar scanner. The main stratigraphic surfaces and architectural elements identified using traditional field methods were interpreted directly onto the digital data, similar to seismic interpretation, providing a detailed 3D outcrop interpretation. These outcrop-constrained stratigraphic data were used to construct a 3D zone-based reservoir model. Petrophysical properties from producing analog reservoirs of similar depositional settings were assigned to lithofacies zones. Use of property transforms allowed an accurate representation of intra-zone facies asymmetry.
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Multisource Data Integration and 3D Digital Outcrop Visualization Environment - From Virtual Geology to Subsurface Models
Authors N. Lisi, S. Nardon, G. Brandazzi and E. OrsiniClassical Digital Outcrop modelling (DOM) needs to integrate all the available outcrop-based geologic features that are spatially positioned and recorded, at all scales, in 3D georeferenced environment. To do this, many different tools, with contrasting workflows, are commonly used by various modelers. To methodically integrate and quantitatively use all the various types of geological information retrievable from outcrops Eni decided to create an integrated workflow to be used in a single work-environment and able to run on any Eni infrastructure.This will allow for the user to: - Import, integrate and visualize of all kinds of georefenced data (LIDAR, GPR, Shallow Seismic, GPS measurements, wellbore logs and bottom-hole core picture, etc) in both 1D, 2D and 3D domain - interpret data in terms of surfaces and boundaries via semi-automatic polyline interpretation and picking - use sedimentary facies recognition to extract geometrical information - measure and analyse structural data (bedding and fracture plunge) both from LIDAR Clouds of Point and photodraped images A robust Virtual Outcrop has so been produced and will be expanded in the future providing the outcrops are suitable to be used as subsurface analogs.
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High Resolution 3D Mechanical Earth Model Using Seismic Neural Netmodeling - Integrating Geological, Petrophysical and Ge
Authors A. S. Wendt, F. R. Mohamed, A. Rasmussen and A. MurinedduA 3D Mechanical Earth Model (3D MEM) was built integrating geological, petrophysical and geophysical data. The 3D MEM represented the close-to-initial rock property conditions, and is an ideal basis for e.g. wellbore stability and formation integrity forecasting during initial and depleted field conditions. Using neural networking, dynamic rock properties at the wellbore level and derived from seismic inversion were integrated to obtain a "true" 3D property model. The lateral resolution of the model was driven by seismic trace density; the vertical resolution was driven by upscaled well log information. The workflow was developed for constraining regional property trends, that honor structural elements in the field, and allow to derive realistic rock property values and distributions even in areas where only limited well log information exists. The 3D MEM demonstrated that (1) Neural networking driven by seismic inversion produces rock property values that are nearly identical with the upscaled logs, which is a remarkable improvement; (2) The distribution of the rock properties is controlled by main structural elements such as faults, erosional surfaces, layering and topography; and (3) The distribution of the rock properties has a high lateral and vertical resolution even in areas where wellbore information was sparse.
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A Software Agent Based Tool for Generating and Validating Structural Interpretations
Authors B. Zhu, M. Perrin, Z. Guessoum and J. F. RainaudThe paper examines the problem of validating the geological interpretation related to a 3D structural model in view of new information coming from a drilling in progress. Considering a given geological interpretation expressed as a Geological Evolution Schema [Brandel & al. 2005], there exists definite rules that allow to determine whether the markers corresponding to two geological surfaces can be neighbours or not along a drilling trajectory. The validation problem then consists in checking the compatibilities of the various couples of markers successively met by the drilling trajectory. This is by nature a distributed problem. We propose to model it by means of a Multi-Agent System [Bradshaw 1997, Briot and Demazeau 2001] and to solve it thanks to an Eco-Problem Solving methodology [Ferber 1999]. Preliminary results are given, which demonstrate that the proposed method is sound and promising.
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A Genetic Algorithm for Optimal Blocking of Well Logs
More LessBlocking well logs is an initial and mandatory step for many processes. It is an upscaling procedure and has no unique solution. In order to find a set of "optimal blocking" for geophysical applications we propose to use a criterion based on seismic difference between synthetic seismogram computed on the fine scale logs and synthetic seismogram computed on the blocked logs. The optimisation process is performed with a genetic algorithm because genetic algorithms have the ability to solve non linear problem and to provide a set of solutions which gives an idea of the uncertainty in the model space. Thanks to the limited number of parameters, blocked well logs can be used lately in many applications such as Massive Modelling.
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M-GS - New Spatial Estimation and Simulation Models for More Precision and More Realism
Authors C. Magneron and F. PetitThe majority of the geostatistical models used in the petroleum industry are variogram-based models. The variogram enables to build effective estimation (kriging) and simulation operators by catching the mean spatial correlation inherent to a data set. Despite their popularity, variogram-based models are the subject of several criticisms. The main one is that they should not be able to handle and reproduce precisely the structural complexity of the reality. M-GS models are improved variogram-based models. They are based on an optimized determination of structural and computational parameters. They lead to more precise and/or more realistic estimation and simulation results than conventional variogram-based models. It is shown by four examples regarding gridding (2), noise removal and simulation issues.
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Earth Recursion, an Important Component in Shared Earth Model Builders
Authors S. A. Petersen and Ø. HjelleThe concept of Earth Recursion is introduced to solve critical problems of Shared Earth Model builders, especially related to their capability to express the geological evolution. The recursive approach turns out to be very efficient when addressing apparently diverse questions like natural "aging", property depth trends, incorporation of externally defined property distributions, faults within volumes and structural restoration. The concept is implemented in the Compound Earth Model builder by StatoilHydro. It is shown how the original expression for spatial distribution of properties can be written as a recursive sequence. This revision forms the basis for the implementation of Earth Recursion in the builder and demonstrated by construction of a complex property distribution reflecting the interference of on-lapping features, normal faulting and compression.
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Complex Volcanic Reservoir Characterization - A Case Study for Southern Songliao Basin, Northeast China
More LessDiscovery of a gas accumulation in Lower Cretaceous YingCheng Group volcanic rocks was confirmed by an exploration well in the southern part of Songliao Basin, Northeast China. A workflow and accompanying modified methodologies were applied to compute gas in place (GIP), which innovated from a similar study for the northern part of Songliao Basin. There were 3 volcanic sequences identified in Yincheng formation with 3 major domes on top of the sequences. The lithology was dominated by effusive deposits of rhyolitic composition and interbedded with minor explosive tuffs and tuff breccias. Several vertical and lateral lithology distribution patterns were identified to allow reconstruction of the sequence of volcanic events. Porosity was vesicular, fracture and vuggy along with fracture in lava flows, and micropores, vuggy leached in the pyroclastics and in-situ breccias. Multiple well pressure data analysis indicated that there was an unified pressure system, and that saturations could be obtained from a saturation-height function above free water level and the capillary pressure curves. A reservoir model was built with semi-deterministic simulation and used to calculate reserves in-place.
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Sensor Technology Comparison Method and Case Study, Part I
Authors D. Yu, B. Maechler and F. MayoSensor performance is vital to the quality of seismic image and detailed comparative study between the velocity and acceleration types will enhance a deeper understanding. In the analytical approach in Part I, it is demonstrated that the time delay of analog geophone data can be as large as 0.12 ms, depending on input signal spectrum, the range of sensor variances, and the deconvolution process; but a typical accelerometer time delay is only 10 μs. It also discusses the issue of the low frequency attenuation by geophones, in contrast to an accelerometer’s flat response to DC. Further digital synthesis analysis in part II provides further quantifying evidences of performance differentiators by statistical measures in terms of time delay, correlation and coherence.
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Laboratory Comparison of the Performance of Analog Geophones and MEMS Accelerometers
Authors G. Hauer, M. Hons, R. Stewart and S. SpiewakA seismic sensor testing laboratory at the University of Calgary is evaluating the performance of analog geophones and MEMS accelerometers using precise mechanical excitation. It is important to characterize the errors in the experimental results as being due to the imperfection of the sensors in addition to the distortions of the testing equipment during excitation. Seismic grade geophones and MEMS accelerometers both exhibit excellent performance as compared to their theoretical models down to measured acceleration amplitudes of less than 10 micro-g.
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Accelerometer Versus Geophone Response - A Field Case History
Authors M. S. Hons, R. R. Stewart, G. Hauer, D. C. Lawton and M. B. BertramA method is derived for the calculation of ground acceleration from geophone data using a frequency-domain inverse filter and an empirical scaling constant. Acceleration-domain spectra from geophones and MEMS survey at Violet Grove, Alberta, Canada are compared. We find that the geophone and accelerometer data, over a band of 5-200 Hz, are very similar. The accelerometer amplitudes are larger than the geophones' below 5 Hz and there are some differences at very high first breaks are not observed on the accelerometer records at some stations.
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Electronic Gimballed Geophones for Ocean Bottom Seismic Systems
Authors T. Buettgenbach, M. Bolduan and K. SchleisiekToday's multi component seismic acquisition systems suffer from orientation problems if they are deployed in inaccessible environments like the deep sea (OBCs, OBSes and seafloor observatories). If MEMS are no viable alternative because of internal noise, power, or dynamic range constraints, 15 Hz geophones, or costly mechanical gimbal systems had to be used in the past. A "Full-Tilt" 4.5 Hz geophone will be presented as a cost effective alternative that operates in any orientation at low geophone noise and distortion levels. An integrated position sensor keeps the geophone's coil in its center position due to an electronic feedback arrangement that produces a compensation current, which is proportional to sine of the tilt angle. A tiny fraction of this compensation current is added to the seismic signal. Therefore, the Z-component of a 3 axis arrangement can be accurately determined by vector rotation in a first post-processing step automatically. Data of a study about the intrinsic noise will be presented. Also data from a measurement at the seafloor will be shown, comparing signals of Full-Tilt geophones to signals of MEMS accelerometers.
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Vibrator Data Quality Prediction from Remote Sensing-based Near-surface Analysis
More LessRemote sensing allows a spatially dense look into the near surface. By leveraging technology such as multispectral satellite data, experienced users are able to create maps that aid logistics planning for surface seismic acquisition and give an estimation of data quality that can be achieved. This paper draws upon examples from a seismic survey in a coastal area of the UAE. We demonstrate that the integration of Landsat 7 ETM imagery calibrated by selected surface geology sampling makes it possible to predict probable instances of wet sabkha, investigate the correlation between the multispectral remote sensing data, and correlate the vibrator sweep performance data with the near surface. The integration of the data is aided by a GIS database.
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Reducing Harmonic Distortion on Vibrators - Stiffening the Vibrator Baseplate
By Z. WeiDue to non-linear effects, the ground-force signal transmitted into the subsurface by vibrators is contaminated by harmonics. The lack of ideal rigidity of the baseplate contributes to the overall harmonic content of the vibrator output. The baseplate flexure exacerbates harmonic distortion, especially the 2nd harmonic distortion. Meanwhile, the ground-force approximated by the weighted-sum method is limited to a narrow frequency bandwidth due to the low baseplate rigidity. A new baseplate design significantly increases the stiffness of the baseplate and dramatically reduces its flexure. The new baseplate is 2.5 times stiffer than the standard baseplate while only suffering a 5% increase to its weight. Field testing demonstrates that with the new baseplate the validity of the weighted-sum ground force in a frequency range up to 160 Hz is achieved. Meantime, the suppression of the even order harmonics contained in the ground force is observed. Very significant harmonic distortion reduction is achieved as the vibrator is on hard and/or uneven ground.
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Independent Simultaneous Sweeping
Authors D. Howe, A. J. Allen, M. S. Foster, I. J. Jack and B. TaylorIt is well known that higher fold and increased sampling is a sure path to improved data quality, and that vibroseis productivity rates are often the limiting factor on land 3D surveys. We want to find ways to use multiple sources simultaneously, so as to make a step change in both sampling density and productivity. In 2006 BP carried out a test of a very simple simultaneous vibroseis method, which we call ISS (Independent Simultaneous Sweeping). In this method all vibrators worked independently without any attempt to synchronise their activity, and the underlying principle of this test was that all interference between sources should be treated as ‘noise’. The noise was randomised as much as possible, and a standard suite of noise removal tools was used during processing. There was no requirement for specialised wavefield separation techniques. In this simple and robust approach, there is no apparent limit to the number of sources that can be operated simultaneously, there is no waiting time for any vibrator, and very little central control or communication is required. It is very well suited for work in many environments including difficult terrain, where vibrator manoeuvring is slow, or where radio communication is challenged.
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Simultaneous Sourcing without Compromise
Authors C. E. Krohn and R. NeelamaniWe show that iterative methods can improve the separation and remove noise for seismograms recorded with multiple vibrators operating simultaneously with a single sweep. Interference noise arises because multiple seismograms need to be recovered or separated from a smaller number of vibroseis field records. This noise represents a compromise made for high efficiency acquisition compared to methods, such as HFVS (High Fidelity Vibratory Seismic), in which there are as many sweeps as there are vibrators. The iterative methods start with an initial separation to as many seismograms as there are vibrators. Then updated seismograms are produced by adjusting them to match the survey data and to satisfy characteristics of noise-free seismograms. The iterations can be repeated until the measure of error is satisfactory. The match to survey data involves reconvolving parts of the initial seismograms with an estimate of the vibrator signatures and stacking. The characteristics of noise-free seismograms can include the fact that signal decreases with time but noise does not. We show improved separation and reduced noise for both pseudo-random sweeping and for long segmented sweeps (Continuous-HFVS). With these iterative methods, the full efficiency of simultaneous sourcing can be obtained without a noise compromise.
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Converted-wave Imaging in the Caspian Sea - A View of Mud Volcanoes
Authors R. G. K. Johnston and P. ParamoBP's field developments in the Caspian Sea are being enabled by ocean-bottom seismic (OBS), almost exclusively through wide-azimuth P-wave imaging. Mud volcano-related features, once thought to act like diffuse gas clouds to P-waves, complicate the propagation of P-to-S (PS) converted waves and are not invisible to them. Following initial data processing of two OBS surveys in 2003 and 2004, an internal study into data quality and propagation issues associated with PS waves focused on understanding how much of the poor imaging was fundamental to the data, and how much could be improved through data processing and more-refined model building. Processing trials supplemented by forward modelling of plausible scenarios for the internal geometries of the mud volcanoes begin to explain the range of PS image quality within each OBS survey, and between surveys, as well as the conundrum of poor PS image quality where P-wave imaging is not overly compromised. This suggests discrete zones of poorly-consolidated, possibly fluidised, material which have a significant impact on PS propagation. So far this has proved as much of a challenge in many areas as the effects of distributed gas on PP propagation.
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Improved Imaging Using Ocean Bottom Seismic in the Snøhvit Field
Authors G. Ronholt, H. A. Aronsen, M. S. Guttormsen, S. Johansen and L. KlefstadThe StatoilHydro-operated Snøhvit field is currently in the final preparatory stages of gas production. A thin oil column is present below the gas in the area. Poor seismic imaging in the western part of the field, due to shallow gas, has led to uncertainties in both seismic interpretation and hydrocarbon volume calculation. To reduce these uncertainties, ocean bottom cable seismic (OBC) data were acquired in late 2006. The OBC data were processed by CGGVeritas in 2007. A complex 4 component (4C) processing sequence was implemented along with extensive shear-wave statics work and imaging through anisotropic compressional (P reflected to P) and converted (P converted to S) wave pre-stack depth migrations (PSDM). The resulting PSDM OBC data images in the area beneath the shallow gas are significantly better than the images from streamer data. The PP images show that multi azimuth imaging, to a large extent, solves the illumination problems beneath the shallow gas. The PS images do not show signs of the high attenuation effects we see in the PP images. The combination of P and S velocity model building also allowed us to solve the shallow gas in the velocity model.
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Using 3D4C Data to Image and Interpret the Seismically Obscured Area over the Tommeliten Alpha Discovery
Authors G. Iversen, B. Lyngnes and T. StrandA high density 3D4C seismic survey was acquired over the Tommeliten Alpha gas condensate discovery in 2005 to image a seismically obscured area caused by complex velocity and density variations in the overburden. Both full azimuth PP and PS data were used and pre-stack co-depth migrated. The result was an improved image of the previously obscured area, especially in the PS dataset. The size of the Seismically Obscured Area (SOA) was reduced also in the pre-stack depth migrated PP data, but in this outer part of the SOA the PP data gave a different image compared to the PS dataset - making the interpretation challenging. Although the resolution of the PS data is lower at the target level, and the main Ekofisk Fm reservoir target (21-24m thick) is below PS seismic resolution, the PS dataset proved very useful in mapping the structural shape and faults inside the SOA, leaving only a small central area obscured.
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Depth Imaging beneath a Seismic Obscured Area (SOA) and Analyzing Its Character - Eldfisk Field Experience
Authors O. Knoth and N. D. WhitmoreTo overcome the challenge of imaging beneath a previously seismic obscured area (SOA) ConocoPhillips(CoP) and its partners used depth imaging utilizing OBC data with converted waves on the Eldfisk field. The imaging challenge is caused by overburden effects predominantly in the Miocene interval. Laterally compact low velocity streaks combined with compartmentalized and overpressured thick shales distort the wave field traveling through it. In 2006/2007 CoP and its co-ventures reprocessed the 2001 OBC data with emphasis on improved multiple attenuation, converted wave preprocessing and depth imaging to uplift the reservoir image within the SOA area. This resulted in a significant reduction of the SOA area (conservative ~30%) for the pressure data and a much improved converted wave image of the reservoir compared to previous results. The velocity field used in depth imaging was consistent with the expectations of a sharp lateral transition and exhibited both extremely low velocities (1450m/s at around 1.8 km depth) and sharp lateral transition (up to 30% reduction for 1000m lateral distance). The workflows and techniques were novel with respect to the role detailed interpretation played in the constraint tomography and how synthetic modeling helped to understand the imaging problem at hand.
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Unconventional 3D Seismic Land Acquisition in Abu Dhabi
Authors G. Ajlani, O. Suwaina and M. Al-KaabiAbu Dhabi National Oil Company (ADNOC) recently acquired a land vibroseis 3D seismic survey in high dunes area where through extensive pre-survey modeling of reservoir requirements and matching with survey design and acquisition parameters, excellent data quality has been achieved at target levels with successful and highly efficient operational performance. Traditionally, land 3D seismic data acquisition in Abu Dhabi has been characterized by large source and receiver arrays, many long high frequency sweeps, large migration aperture area and limited number of active channels caused by equipment limitations. Over the years the survey geometries have evolved to the use of smaller source and receiver arrays and smaller source arrays with single sweeps. In this project, the near-surface conditions in the form of 300 meters high and steep sand dunes interrupted by numerous sabkhas coupled with target reservoirs which are significantly different and much deeper than the rest of the province, presented significant challenges. This led to the need for different set of parameters for a fit-for-purpose seismic survey for reservoir characterization requirements at a certain formation at a specific depth range in a difficult data area. Additionally, project duration and cost requirements dictated the need to optimize migration aperture and patch layout.
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Field Test of the Point Receiver Land Acquisition Technology Performed in Timimoun, Algeria
More LessAn acquisition field test was performed in Algeria to assess the benefits of point receiver recording for enhancing the resolution and signal/noise ratio of land seismic surveys. Recording point receivers (or point sources) instead of the conventional receiver or source arrays enables pre-processing (such as intra-array static and amplitude corrections, surface noise attenuation) to be applied before Digital Group Forming (DGF). Point receivers were simulated by bunching at the same location the six geophones of each string and a dense strip of 4 lines of 6 km of "point receivers" was deployed with a fine sampling of 6.25 m X 6.25 m. These additional test lines were simultaneously recorded with the regular 3D receiver spread. Causing a minimal delay to the 3D operations, a point receiver 3D dataset of 2 km X 9 km was then recorded and compared to a 3D reference dataset of equivalent fold and geometry. Equivalent but independent processing sequences were applied to both datasets, except the above pre-processing applied to point receivers before DGF. The results are encouraging for the use of point receiver technology in improving signal/noise and bandwidth in this area.
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Comparison of Conventional Geophones Versus Digital Sensor - Preliminary Results from 2D Field Test Exercise
Authors F. Mancini, J. M. Mougenot and J. SuiterIn recent years digital single sensors (MEMS) have become a viable option to conventional geophone arrays for land acquisitions, both operationally and economically. Different advantages and disadvantages of single sensors are mentioned in the literature, such as broadband response, linear phase and amplitude response, lower weight, but also lack of array power for noise attenuation and higher costs. TOTAL decided to compare the two receiver systems during an acquisition feasibility test consisting of two 2D lines acquired in parallel with the same source. Results showed that the noise complexity of the data was better handled by geophone arrays. In order to get comparable results with single sensors, a dense distribution is required which could be difficult for a large 3D study. We also learned that single sensor data require specific processing to compensate for the lack of array filtering capability.
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Enhancing the Low-frequency Content of Vibroseis Acquisition - A Case History from the Minagish Field
Authors C. Bagaini, A. El-Emam and A. ShabrawiSeveral recent advances in land seismic acquisition equipment and software have encouraged the exploration geophysicists to reconsider the potential benefits of energetic low frequencies for geophysical applications such as imaging beneath high velocity and highly absorbing formations, deep imaging, inversion of surface waves to characterize the near-surface elastic properties, velocity model estimation in geophysically complex areas and acoustic impedance inversion. We briefly review the more relevant advances in land seismic acquisition and present their application to a recently acquired 3D seismic survey over the Minagish field in Kuwait.
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Utilizing Multi-azimuth Streamer Data for Reservoir Characterization and Uncertainty Analysis in the Nile Delta
Authors R. Marten, W. Rietveld, M. Benson, A. Khodeir, J. Keggin and P. CookMany authors have written about the imaging benefits of multi-azimuth seismic data, extolling the virtues of this type of acquisition as a way to defeat multiple diffractions, improve illumination and produce a better stacked image. Consequently, multi-azimuth streamer seismic data holds out the promise of producing a seismic image much richer in signal and resolution than its single azimuth equivalent. This acquisition strategy in the offshore environment could ultimately allow a much clearer picture of the subsurface where one had not existed before. A number of studies have borne this out, showing the benefits for interpretation of structure and seismic stratigraphy. Beyond these well understood benefits of multi-azimuth seismic for imaging, these data may also offer a unique opportunity to further characterize the reservoir based on multiple independent measures of the overburden and reservoir. The purpose of this paper is to present a case study at the Raven discovery utilizing multi-azimuth data for reservoir characterization and uncertainty analysis.
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Instantaneous Isochrons, Volume-flattening and a High Resolution View of Sedimentation Rate
Authors J. E. Rickett, J. Lomask and J. ClarkThe instantaneous isochron attribute is defined as the change in seismic time with respect to relative chronostratigraphic time. It can be computed by taking the derivative of a horizon volume used for volumetric flattening. In an example from Angola, the horizon volume is computed automatically with a global algorithm that picks every horizon in a 3D dataset. The instantaneous isochron attribute derived from this provides a dramatic view of the geomorphology of a turbidite sequence.
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High Frequencies Attenuation and Low Frequency Shadows in Seismic Data Caused by Gas Chimneys, Onshore Ecuador
Authors F. G. C. Brouwer, A. Welsh, D. L. Connolly, C. Selva, D. Curia and A. HuckHydrocarbon reservoirs can be sources or sinks for migrating gas, hence gas chimneys have an inherent correlation with HC reservoirs. If frequency effects show a strong correlation between reservoirs and gas chimneys, observing attenuation zones above reservoirs can be considered an equivalent indicator. Loss of seismic data quality is usually the main characteristic of gas chimneys but it is hoped that in the future we can use high frequency observations with CWT as an alternative method to detect gas clouds correlating with reservoirs, even in cases where there is no apparent loss of data quality. In this case study, using spectral decomposition techniques, zones of high frequency attenuation can be observed in seismic data above onshore sandstone oil reservoirs in Ecuador. This attenuation correlates directly with gas chimneys seen in the seismic volume. The amount of attenuation is dependent on the vertical extent of chimneys. Low frequency shadows of reflectors at reservoir depth can also be observed and correlated laterally with the extent of shallower gas chimney zones directly above. Intrinsic attenuation of seismic waves through gas chimneys is proposed as a likely cause of these frequency effects.
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Automated Geomodelling a Nigeria Case Study
More LessA methodology for automated 3D seismic volume interpretation is presented. Stack of horizons are generated from the 3D volume along with the faults. These horizons can then be used to build a geological model and better visualization of the depositional model. PaleoScan is a new technology to fast track interpretation of large seismic volumes with an innovative geo-model computation method, based on image processing and optimization techniques. In this work we describe a case study in offshore Nigeria where PaleoScan has been effectively used to map stratigraphic features and reservoir distribution and also build a robust structural model based on the generated horizon and fault cube.
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Gleaning Meaningful Information from Seismic Attributes
Authors S. Chopra and K. J. MarfurtPoststack seismic data loaded on workstations for interpretation exhibit a certain level of noise. This noise could be of various sorts - acquisition related, processing artifacts or random. In this presentation we focus on conditioning our seismic data prior to attribute computation. We discuss the use of some of the procedural steps for noise filtering and dip-steering options for computation of some geometric attributes like coherence and curvature. In addition, we discuss the impact the choice of algorithm can have on the final results. All these factors ensure that the seismic attributes yield more accurate information for interpretation.
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Volume Blending with Directional Seismic Attributes
By A. E. BarnesVolume blending is a powerful tool for multi-attribute analysis, but its use is limited largely to coherence, reflection strength, and the original seismic data. The success of discontinuity in blending has overshadowed the potential of complementary attributes, especially directional attributes such as amplitude gradients, azimuth, directional dip, and seismic shaded relief. Directional attributes make seismic data appear like illuminated apparent topography, which aids intuition. Amplitude gradients have seen little use but should be explored as they can reveal details not seen in other attributes. Shaded relief is the most powerful directional attribute, but azimuth and directional dip are useful substitutes. Smoothing directional attributes improves them for blending.
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An Approach of Seismic Interpretation Based on Cognitive Vision
Authors P. Verney, M. Perrin, M. Thonnat and J. F. RainaudAdvanced seismic interpretation most commonly rests on transforming original data representations by considering more or less numerous seismic attributes, which bear no explicit relation with geology. For this reason, they hardly allow fully solving problems such as reassembling sparse geological surface elements or specifying chronological or topological relationships between surfaces such as unconformity, on lap, interruption by fault. The present work intends to make further progress in geology-based interpretation of seismic data by using artificial intelligence tools based on cognitive vision. We propose a cognitive vision workflow for seismic interpretation based on a visual ontology and on three associated module dealing for data management, visual characterisation and geological correlation. An example of results is given showing the possibilities of the method for easily merging disconnected reflectors within one stratigraphical horizon taking into account simple geological criteria (amplitude, thickness, dip, vertical distance between reflectors).
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Fundamental Principles of Isotropic Marine Source Design
Authors J. Hopperstad, R. Laws and E. KraghWe discuss how to design a marine source array that emits the same pulse shape in all directions. We do this by analysing the relative contribution of the three main components of the farfield source spectrum: the ghost response, the aperture smoothing function, and the monopole spectra of the individual source elements. Counter to intuition, reducing the lateral array dimensions, such that it approximates a point aperture, will not result in an isotropic source; it will create a dipole because of the sea-surface reflection. For single depth arrays, the lateral geometry must be tailored such that the aperture smoothing function offsets the angular variation of the ghost response, in particular at frequencies close to the first ghost notch. Multi-depth arrays can be made insensitive to the lateral geometry by combining the source depths, such that the first ghost notch is far beyond the highest frequency of interest. This results in smaller spectral variation with take-off angle than that of single depth arrays. There is no advantage in using more than two layers.
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Are Seismic Sources Too Loud?
Authors R. M. Laws, E. Kragh and G. MorganIf a seismic survey is performed twice in quick succession the two images will not be exactly the same. Part of the difference results from ambient noise and part is shot-generated. The shot-generated noise originates both from the previous shot and from perturbations to the acquisition, such as small differences in shot and receiver positions. Only if the ambient noise is higher than the shot-generated noise will increasing the source output improve the overall signal-to-noise ratio of the image. We used data from a repeated survey, together with ambient noise measurements, to determine the power spectra of the signal, the ambient noise and the shot-generated noise. We did these tests in both calm weather and poor weather. We show that, in this example, the noise in the seismic image is mostly shot-generated not ambient. This means that the signal-to-noise ratio of the image would be largely unaffected if the source power were reduced. In our test example, for most of the bandwidth, the seismic source is unnecessarily loud.
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Using Onboard Time Lapse Processing for Quality Control of Time Lapse Acquisition on the Norne Fields
Authors B. Osdal, T. Alsos, A. Høiås and H. A. AronsenThis paper will show how onboard processing is used during acquisition in order to quality control the 4D acquisition. The effect of not being on position with source and receivers and the effect of industry noise can be directly analysed using 4D difference data processed onboard. This information is then used in the decision process of reshooting a line or not.
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Improved Marine 4D Repeatability Using an Automated Vessel, Source and Receiver Positioning System
Authors J. O. Paulsen and G. BrownA new automated and integrated, vessel, source, and receiver control system has been developed to improve the accuracy and repeatability of 4D surveys. The new control system replaces operator intervention with automated updates to vessel, source, and streamer steering devices from positioning information from all in-sea equipment. This has lead to a step change in the accuracy of source repeatability (2.5-m repeat accuracy for 95% of shotpoints), and has also improved the ability to repeat receiver positions.
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Benefits of Two-boat 4D Acquisition - An Australian Case Study
Authors T. A. Ridsdill-Smith, D. Flynn and S. DarlingIn February 2007 Woodside acquired a two-boat, push reverse 4D monitor survey over the Enfield oil field in offshore Western Australia (Figure 1). Two-boat push reverse acquisition was used to maximize 4D repeatability and minimize 4D infill in a survey area known for strong, unpredictable currents. The source and receiver positional repeatability obtained in the monitor is good with a mean |Dsrc|+|Drec| of 27m at the target offset of 1900m. Survey infill is only 7% compared to a predicted infill of 30% to achieve the same 4D coverage with oneboat acquisition. Shortcomings of the two-boat push reverse technique include a large minimum near offset of around 500m and a receiver motion 4D error when matching to the conventional one boat baseline survey. An NRMS of 15% was obtained for the final processed data. Following the success of the 2007 Enfield survey, Woodside has proposed to acquire a second two-boat monitor survey on Enfield in early 2008.
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The Concept of Triple Over/Under Streamer Data Acquisition and Processing
More LessMarine seismic data acquired with towed pressure sensing streamers suffers from the interference of the upgoing wave with the downgoing wave reflected at the sea surface. The downgoing wave introduces time-variant perturbations due to the time-variant shape of the sea surface, especially in rough weather conditions, meaning that the sea-surface ghost becomes time variant. These problems can only partly be overcome if a single streamer is replaced by a pair of streamers such that one streamer is towed vertically above the other. The basic dilemma with twin-streamer data is that one has to make a data processing decision: either to attenuate the downgoing wave to reduce the rough-sea perturbations while introducing a pseudo ghost, still attenuating the signal energy at certain frequencies, or to estimate the upgoing wavefield, while leaving the rough-sea surface perturbations still affecting the output data. If one accepts to stay with pressure sensing towed streamers, the situation changes drastically if at least one further streamer is added vertically to the twin-streamer pair. With such an extended over/under streamer configuration one can derive an estimate of the upgoing wave at the flat sea surface, whatever the actual sea-surface state is.
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GeoStreamer, a Dual-sensor Towed Marine Streamer
Authors R. Tenghamn, S. Vaage and C. BorresenThis paper reports the successful implementation of particle velocity sensors in a new dual-sensor towed marine streamer and presents examples of acquired and processed data from that streamer. Properly combining the recorded signals from the particle velocity sensors with those from the hydrophones cancels sea-surface ghost reflections and removes the notches from the data’s frequency spectrum caused by those ghost reflections. As a result, the streamer can be towed deeper below the sea surface than is currently practicable, and the data are much less affected by weather noise, without compromising its bandwidth. In fact, the bandwidth of the recorded data is increased.
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Wave-height-corrected Seismic Data
Authors R. J. Goto, E. Kragh, R. Laws, W. G. Morgan and R. PhillipsThe rough sea surface perturbs, to first order, the receiver ghost arrival time and introduces a source array static. We discuss how to measure and correct for both the receiver and the source perturbations for seismic data acquired in rough seas. For the receivers, ultralow (sub 1 Hz) pressure variations recorded by the hydrophones are inverted for wave height profiles which are both time and space variant. Local (compact) deconvolution operators are then used to stabilize the receiver ghost. For the source, real-time kinematic (RTK) GPS measurements accurately track the height of the source floats and a static correction is made at the time of each shot. Previously published work has concentrated on measuring and validating these errors, particularly on the receiver side, but corrections have not been applied to seismic data. Here, we show application of such corrections to seismic data acquired in rough seas. The resulting data show improved reflector continuity and a stabilized wavelet. Data repeatability is improved and the resulting data are more suitable for high-resolution surveys and time-lapse reservoir monitoring applications.
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Data Driven Velocity Model Building - An Application to Egypt Nile Delta
Authors M. C. Tanis, T. P. Summers, P. Cook and J. KegginThe complex Messinian layer in the Egypt Nile Delta poses a serious challenge to the building of an accurate velocity model and to the imaging of structures that lie below this interval that consists of interleaved anhydrite, shale and other facies. Conventional prestack velocity analysis, depth imaging and tomography provide only a limited solution to this complex velocity modeling and imaging problem. While the recent acquisition of multi azimuth data over this area aimed to address both the imaging and illumination below the anhydrite, building a reliable velocity model for prestack depth migration still remains a challenge. Here we present a novel approach to model these complex Messinian anhydrite layers interleaved with other thin sediments directly from seismic data using a binary style velocity modeling approach. The method is based on exploiting the distinct seismic character of anhydrite and estimating it directly from inverted section of an optimized migrated stack. Application of this procedure to data from Egypt Nile Delta shows that the technique can provide a reliable high resolution starting velocity model that can be further improved by iterative migration velocity analysis.
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CRS-PreSTM/CRS-PreSDM - Noise Reduction in Seismic Imaging
Authors H. Trappe, G. Gierse, G. L. Eisenberg-Klein and J. PruessmannWith the CRS method the incoherent seismic energy (noise) can be strongly suppressed. The increased stacking/gather fold, and additional wavefield attributes used in the time and depth domain processing enhance the imaging quality in both domains. The CRS time domain processing provides the requisites for an enhanced prestack depth migration with high potential, especially for data with low acquisition fold or high noise levels, where the velocity model is not too complex. The additional wavefield attributes can be used to enhance the velocity model in a robust noise-insensitive procedure, and to design migration operators. The field data examples of the CRS-PreSTM and CRS-PreSDM work flow reveal the high potential of noise reduction for seismic time and depth domain imaging. The key for the improved quality is the combined usage of the CRS attributes for the time domain S/N enhanced processing and regularization, the enhanced velocity building especially for noise contaminated data, and the migration parametrization in combination.
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Staged Subsalt Derisking for Development of the Cleaver Bank High
Authors R. van Boom, B. Spaargaren, A. Fongers and R. WervelmanFor many years the west of 49/14b, offshore U.K. was poorly imaged due to a complex en-echelon system of salt ridges. These issues prevented the development of Carrack West. In 2006 a seismic survey with a different azimuth, and longer offset was acquired. During the first stages of the processing the interpretation started on the Post-STM. A Pre-STM was delivered together with a Kirchhoff Pre-SDM. The Kirchhoff Pre-SDM on the 2006 dataset was encouraging, it was also noted that the vintage seismic, shot under a different azimuth, showed more energy in certain areas and a dual azimuth processing was performed. At the same moment it was realized that the standard approach of single valued Kirchhoff did not cater for the complex ray-paths in parts of this setting. A WEM enabled us to improve the imaging even further. It is demonstrated that the 5 different datasets all have their own merits. The minute mapping that was needed for the development planning of the Carrack West discovery profited from the parallel use of all the products and only now we are confident on the risk level to take the development of the project further.
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Azimuthal Anisotropy Correction in Champion West 3D Survey - A Case Study
Authors J. Sun, Y. Yin, B. Hung, R. Dike, J. DePledge, Y. Liu and R. WombellIn this paper we present a case study describing the application of a correction for azimuthal velocity anisotropy on the Champion West 3D seismic survey, offshore Brunei. The survey consisted of conventional sail lines, plus regions of two-boat undershoot in the area of existing platforms. The undershooting resulted in very large azimuth variation, and irregular data coverage especially in near offset range. Coupled with the regional azimuthal velocity anisotropy, the large difference in trace azimuths caused time jitters in data, which in turn caused difficulty in imaging. In this study, an azimuthal differential NMO was applied to the data, after scanning for the anisotropy parameters on the basis of stack response. The correction made major improvement to the data, as seen both before and after migration. Before migration, jitters were moderated and stack response was better. After migration, the improvement was seen as better focusing and greatly reduced amplitude striping.
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Increased Resolution of Seismic Data from a Dual-sensor Streamer Cable
Authors D. H. Carlson, W. Söllner, H. Tabti, A. J. Day and M. WidmaierTraditionally, towed marine cables measure the seismic wave-field using only hydrophones. A new solid core dual sensor cable has been introduced that measures simultaneously the pressure using hydrophones and the vertical component of the particle velocity using motion sensors. The first of many advantages of measuring the dual wave-field is that the two measures can be combined to separate the wave-field into up-going and down-going components. This method may be used to derive the up-going pressure field, thereby eliminating the receiver ghost. This gives increased bandwidth for both low and high frequencies, which consequently enhances resolution and signal penetration. Another advantage, and the reason for the added low frequencies, is that, since the receiver ghost can be suppressed, the streamer can be towed at greater depth where it encounters reduced acquisition noise thus improving the ability to acquire data during rough weather. This paper illustrates these applications using 2-D field test data that was acquired concurrently with a survey that used a conventional (hydrophone only) cable.
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Deepwater Gulf of Mexico - Benefits of Integrating Seismic, Gravity and Magnetic Data in a Sub-salt Environment
Authors A. G. Blacque, K. Mohn, S. V. Yalamanchili, A. Morgan and V. EgorovTechnical innovation in the Gulf of Mexico has been pushing the frontiers of petroleum exploration, leading to the expansion of proven play concepts into new areas of the deepwater Gulf of Mexico. Operators are now targeting structurally controlled traps containing Paleogene (Wilcox) sands, beneath the Louanne salt canopy. Understanding these deepwater sub-salt opportunities requires a regional, structural and stratigraphic context for the Wilcox play. Sub-salt sediment distribution, salt geometry, basement architecture and basement composition are all crucial to this workflow. Although many studies have been undertaken to better understand this sub-salt petroleum system, the fundamental problem of sub-salt seismic imaging remains the key challenge, even with the latest acquisition and processing technologies available. Through integrating seismic, gravity and magnetic data, better understanding of the sub-salt environment has been achieved. As a result of detailed integration, a new basement map has been created from high-resolution aeromagnetic data and Pre Stack Depth Migrated (PSDM) seismic data. Both 2D and 3D earth modeling were then completed to predict spatial distribution of autochthonous salt bodies, basement density and susceptibility variations, location of open/closed salt feeders to the allochthonous canopy and the location of the continental-oceanic boundary.
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Microseismicity of Non-linear Fluid-rock Interactions - From Geothermic Stimulations to Fracturing of Barnett Shales
Authors S. A. Shapiro and C. DinskeBorehole stimulations by fluid injections are common for developments of hydrocarbon and geothermic reservoirs. Often they induce numerous microearthquakes. Spatio-temporal dynamics of such induced microseismic clouds can be used to characterise reservoirs. However, a fluid-induced seismicity can be caused by a wide range of processes. We propose an approach to describing a broad range of non-linear fluid-rock interactions. We show that a linear pore pressure relaxation and a hydraulic fracturing are two asymptotic end members of a set of non-linear diffusional phenomena responsible for seismicity triggering. Microseismicity of Barnett Shales shows signatures of a non-linear diffusional triggering with an extremely strong hydraulic permeability enhancement in a 3-D domain of the reservoir. This indicates a process of a volumetric hydraulic fracturing via reopening of compliant preexisting fractures.
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Nonlinear Pore Pressure Diffusion and Associated Microseismicity in Rocks with Pressure-dependent Permeability
Authors T. M. Mueller and N. HummelThe fluid transport properties of fractured porous rocks usually show a strong dependence on the effective pressure and thus on the pore pressure. Consequently the process of pore pressure diffusion initiated by fluid injection experiments is governed by the non-linear diffusion equation. The spatio-temporal evolution of microseismicity associated with the process of nonlinear pore pressure diffusion is analyzed. In particular, it is shown that the process of nonlinear pore pressure diffusion allows to define two triggering fronts. One corresponding to the triggering of microseismic events without changing the fluid transport properties significantly, another one that triggers the majority of microseismic events and that alters the fluid transport properties significantly. The applicability of this model for the interpretation of microseismicity observed during hydraulic fracturing treatments is discussed.
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Evidence of Hydraulic Fracture Reorientation Across a Thrust Fault
Authors S. C. Maxwell, U. Zimmer, R. Gusek and D. QuirkMicroseismic imaging of a hydraulic fracture stimulation showed significant fracture reorientation across a thrust fault. Fracture orientations were identified through a combination of alignment of event locations, polarization of the seismic waves and injection details. Stimulation below the fault indicated a near horizontal fracture geometry. Above the fault, a near vertical fracture geometry was observed. This difference in fracture geometry was attributed to rotations in the direction of minimum principle stress, which is consistent with observed differences in the injection pressures. The fracture reorientation suggests a significant difference in the stimulated permeable pathways.
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Microseismic Features of Gel and Water Fracturing of Tight Gas Reservoirs
Authors C. Dinske and S. A. ShapiroWe analyse the spatio-temporal dynamics of hydraulic fracturing induced microseismicity. We present a model that describes the growth of a hydraulic fracture as a geometry and diffusion controlled process. This model contributes to estimate important parameters of the fractured area and to better understand underlying physical processes. We apply this model to well documented datasets from fracturing experiments in Cotton Valley tight gas reservoir. The treatments were performed with different parameters, e.g., type of fluid, injection rate, total volume of fluid and of proppant. In case of a gel-based fracturing, the r-t diagram of microseismicity shows signatures of fracture volume growth, fracturing fluid loss as well as a diffusion of the injection pressure. In contrast, in water-based fracturing a diffusion-like growth of microseismic event cloud is not clearly observable. However, for both the gel- as well as the water-based fracturing we obtain very similar estimates of fracture geometry and hydraulic parameters of the reservoir. The difference in permeability of the particular hydraulic fractures is probably caused by the different treatment parameters.
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Case Studies on 2D- and 3D-Time Reverse Modeling of Low-frequency Microtremors - Application to Reservoir Localization
Authors B. Steiner, E. H. Saenger and S. M. SchmalholzA fast and economically attractive procedure to detect hydrocarbon reservoirs is of main interest for the exploration and development of new oil or gas fields. Several studies at different oil and gas fields around the world have shown spectral anomalies with a high degree of correlation to the location and geometry of hydrocarbon reservoirs. It is reported that the narrow-band low frequency (1.5Hz-6Hz) tremor signals measured at the surface may originate from the reservoirs themselves. However, standard localization techniques fail to localize the signals for real data as one observes continuous tremors rather than single events. Time reverse modeling is a promising technique to reliably localize the so called hydrocarbon microtremors. We show with a numerical feasibility study and real data the potential of such an approach. By using a realistic geologic section we demonstrate with 2D- and 3D-Time reverse modeling that it is possible to localize the origin of tremor-signals.
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A Low Frequency, Passive Seismic Experiment over a Carbonate Reservoir in Abu Dhabi – Wavefront and Particle Motion Studi
Authors K. A. Berteussen, M. Y. A. Ali, J. S. Small and B. BarkatA low frequency passive seismic experiment conducted over an onshore carbonate oilfield in Abu Dhabi observed a narrow band of low frequency (2.5 – 2.8 Hz) signals over both the oil reservoir and the water saturated zone (Ali et al., 2007). The possible causes of this low frequency energy are not well understood and it has yet to be demonstrated what types of waves are being observed. In this paper we present results of an investigation carried out to determine the apparent velocities and the azimuth of the wave fronts as well as the particle motion of the recorded low frequency waves. This work is currently ongoing, but the results so far indicates that the observed waves are most likely some type of surface wave and the azimuth to the source is pointing towards the nearest coastline in the area (the Arabian Gulf).
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Seismic Spectroscopy Using Amplified 3C Geophones
Authors P. van Mastrigt and A. Al-Dulaijanion has now been integrated and used on a conventional seismic crew, representing the potential for large cost savings to record spectroscopy data. We believe that the latter is an industry first, initially reported on the I/O Middle East Technical Forum, Abu Dhabi, February 2007. Firm plans are now in place to take full advantage of this emerging technology by integrating spectroscopy recording on a survey-wide scale on the next seismic campaign. Should this materialize, then the resulting spectroscopy measurements will have a spatial redundancy that is really required assess this tool’ value as a reliable DHI.
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Location of and Monitoring with Induced Earthquakes in Oil and Gas Fields
Authors S. Sarkar and M. N. ToksozB048 Location of and Monitoring with Induced Earthquakes in Oil and Gas Fields S. Sarkar* (Massachusetts Institute of Technology) & M.N. Toksoz (Massachusetts Institute of Technology) SUMMARY We present some developments for location of induced seismic events and apply these to field data. Most commonly used earthquake location algorithms do not work for earthquakes in oil and gas fields. Induced earthquakes generally occur in sedimentary basins with alternating high and low velocity layers. Conventional algorithms based on either smooth velocity gradients or layers with increasing velocities cannot handle many thin layers with high and low velocities. In this paper we
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Three-dimensional Reflection Seismics Surfs the Crest of the Platinum Wave (Best of SAGA)
Authors J. Trickett, W. Düweke and S. KockDue to the highly favourable platinum market over the past decade, a substantial investment has gone into the customization of the 3D seismic reflection method for the unique requirements of the Bushveld Igneous Complex. All of the major South African platinum producers have capitalized on these technology advancements for the purposes of mine planning, risk reduction and development. Over and above their primary value as sources of excellent structural information, the high-resolution 3D seismic data volumes hold a tremendous amount of additional geological and geophysical information. Impulse Geophysical Consulting Services (Impulse) has been afforded the latitude to investigate a host of seismic attributes of the Impala Platinum Ltd. (Impala) 3D survey that was undertaken in 2000. Surface drainage patterns, subsurface weathering profiles, the middling distances between the UG2 and Merensky Reefs as well as the distribution and orientation of fault networks, dykes and iron-rich ultramafic pegmatite (IRUP) bodies were evaluated with particular reference to the root-mean square seismic energy values that were originally extracted by the Rock Deformation Research Group (Leeds University, U.K.). Until recently, very little was known about the seismic response of IRUP bodies. A detailed study including the forward modelling of these features (in the form of synthetic seismograms) yielded some useful results: IRUP bodies have high densities and reflect seismic energy where their thicknesses exceed ± 20m (owing to the seismic source bandwith). As a result, the underlying economic targets are relatively poorly imaged where they occur between thick intersections of these ultramafic bodies. Although more frequent in distribution, IRUP intersections that are thinner tend to be relatively transparent to seismic waves and do not result in significant energy losses.
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Geophysical Imaging of a "Blind" Zn-Pb-Ag Deposit
Authors B. Milkereit, W. Qian, H. Ugalde, E. Bongajum and M. GräberProperly constraining the shape and size of an ore body requires a comprehensive database of petrophysical, geophysical and geological information derived from both surface and borehole data. An integrated borehole and surface dc resistivity study enabled us to detect and delineate shallow Zn-Pb-Ag mineralization beneath thick overburden at the Nash Creek exploration area, New Brunswick, Canada. The 2D and 3D conductivity models are supported by downhole resistivity data and geochemical assay data from exploration boreholes.
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TDEM Method for Hydrothermal Water Prospection
Authors A. Menghini, G. Pagano, S. Floris and E. BerniniTDEM prospection allowed to reconstruct tectonic setting of a thermal basin, in Viterbo (Central Italy). A productive well was located at the intersection of two faults evidenced by geophysical data, reaching a depth of 127 m. and providing thermal water (58°C) with high productivity (spontaneous discharge 10 L/Sec). Interesting results were achieved by using offset-mode soundings, so minimizing costs of geophysical prospection. Also preliminary attempts with grounded system were promising.
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Statics in Magnetotellurics - Shift or Model?
Authors W. Soyer, S. Hallinan, R. L. Mackie and W. CummingMagnetotelluric data sets often show signs of significant local galvanic distortion - static shifts in its simplest form - complicating their quantitative analysis. Our accounting for this problem is two-fold. Co-located magnetic TDEM soundings provide representative resistivity estimates of an approximate 1 D near-surface structure, allowing for calibration of the MT apparent resistivity at the highest frequency limit. Remaining distortion that is unaccounted for can be addressed directly and automatically via 3D inversion: as galvanic effects occur equally in the synthetic simulation of the induction process whenever currents cross resistivity interfaces, the inversion algorithm generates shallow near-surface structure that can reproduce the observed statics. Today's increasing computer resources allow for the detailed meshes and small near surface cell sizes necessary for this approach. Constraints on model roughness prevent local statics solutions from affecting the deeper resistivity image in the minimum structure inversion. For some data sets and geological environments, direct inversion for static shift parameters in addition to the above structural approach may be preferred. Applicability of this two-fold approach is demonstrated on a combined MT data set from the geothermal prospect of Glass Mountain, California.
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The Development of a Multi-purpose Geothermal Site in an Urban Area
Authors K-H. A. A. Wolf, A. Willemsen, T. W. Bakker, A. K. T. Wever and D. T. GildingIn May 2007, students of Deft University, Department of Applied Earth Sciences, made for their 23rd lustrum an appraisal study regarding a combination of geothermal energy combined with CO2-injection. According to the pre-study, nine exploration wells in the Delft area show an anticline below the University grounds, which holds various sand bearing members at a depth of about 2 to 2.5 km. One member consists of highly permeable sands, which may produce about 120 m3/hr of water. The expected geothermal temperature of about 75C can be used for new and renovated buildings. In order to drill an injection and production well for geothermal use on a small foot print, a new light weight composite tubing is proposed. It is possible to drill almost weightless with an innovative mobile telescopic rig. The tubing of the injection and production wells also contain a thermoplastic inner wall, which is expected to be less corrosive and less expensive when compared to regular steel tubing. Hence, the option of CO2-injection into the returning water is considered. The two innovative aspects in this feasibility study, i.e. composite drilling and CO2-injection, got the attention of the industry, university and other (non-) governmental organizations.
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From Gas to Geothermal Exploration - A Case Study from the NE-German Basin
Authors I. Moeck, W. Brandt, G. Blöcher, H. G. Holl, G. Zimmermann, A. Saadat, T. Backers and E. HuengesThe sedimentary Lower Permian is a well known target for gas exploration in the North German Basin as part of the South Permian Basin System. In East Germany a huge quantity of well and 2D seismic data were generated from the 1960’s to 1990. We re-evaluated and re-processed some of these data to define potential geothermal reservoirs for power production. Since 2000, a non-productive gas exploration well, drilled in 1990 in the NE German Basin, is used as a geothermal in-situ laboratory for testing recovery strategies in terms if enhancing geothermal systems. After increasing the productivity of the well by several stimulation treatments, a second well was drilled from 2006-2007 to install a well doublet. The design of the new well differs considerably from gas well designs since geothermal wells need to satisfy some requirements like large diameters for housing the submersible pump, directional drilling to allow a set of parallel hydraulic fractures and drilling under near-balanced mud pressure conditions to minimize formation damage. Recently, a massive stimulation campaign increased the productivity of the new well considerably. This article shows the field development of a deep sedimentary reservoir as a integrated study from gas to geothermal exploration using latest technologies.
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Mapping Geothermal Reservoir Using Broadband 2-D MT Survey in Theistareykir, Iceland
Authors G. Yu, A. Gunnarsson, H. Tulinius, K. M. Strack, L. F. He and Z. X. HeThis initial 2-D MT survey has confirmed the finding of previous TEM survey in the Theistareykir field about the existence of a high temperature reservoir under the Theistareykja area, and also outlined better the boundaries of the reservoir along each long 2-D MT survey lines. This study establishes the relationship between resistivity, temperature and lithology. The geophysical exploration activities act as a very important role to help explore and characterize a geothermal reservoir among other geoscience methods for potential geothermal power plant construction project.
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Results of Stimulation Treatments at the Geothermal Research Wells in Groß Schönebeck, Germany
Authors G. Zimmermann, A. Reinicke, W. Brandt, G. Blöcher, H. Milsch, H. Holl, I. Moeck, T. Schulte, A. Saadat and E. HuengesThe aim of this work is to present results of previously performed fracture treatments in the geothermal research well GtGrSk4/05 at Groß Schönebeck. The fracture treatments included three hydraulic stimulations, two in the sandstone section of the Lower Permian and one in the volcanic section. In low permeable volcanic rocks we performed a cyclic waterfrac treatment over 6 days in conjunction with adding low sand concentrations. Flow rates of up to 150 l/s were realized with a total amount of injected water of 13170 m³. Monitoring water level in the offsetting well EGrSk3/90, which is 475 m apart at the final depth, showed a very rapidly water level increase due to the stimulation treatment. A possible explanation might be a fault zone in the volcanic rocks. It was known from previous treatments in the offsetting well that high permeable sandstones do not show a self propping effect, hence we performed two gel proppant treatments in these sandstones to maintain long-term access to the reservoir. A total amount of 100 to of high strength proppants with 500 m³ of cross-linked gel were injected during each treatment. The subsequent production test in conjunction with flowmeter logging showed the success of the treatments.
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Processing Techniques to Extract Surface Wave Dispersion Curve from 3D Seismic Acquisition
Authors L. V. Socco, D. Boiero, C. Comina, S. Foti and R. B. RegeThe wide diffusion of 3D seismic surveying introduces the need of processing techniques able to extract dispersion curves from data acquired with 2D arrays. In this work we evaluate two processing techniques: the multidimensional Fourier transform and the Frequency Domain Beamforming method. Synthetics and real data have been analysed with the two methods for this purpose. Synthetic data has been obtained with a finite elements modelling and the computed dispersion curves have been compared with the theoretical one. In the analysis of real data the obtained dispersion curves have been compared with the one achieved through a linear array acquisition. The two tested processing methods have been able to correctly identify the fundamental and higher modes of propagation. The curves obtained with the two techniques do not differentiates significantly one from the other and are in agreement with the one obtained by a linear array and theoretical one. So, no advantages in choosing a specific method emerges in terms of result quality. However Beamforming method is more expensive for what concerns the computation.
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Retrieving Lateral Variations from Surface Wave Data
Authors D. Boiero and L. V. SoccoThe task of this work is the evaluation of the possibility to identify lateral variation through Surface Wave dispersion analysis even if these techniques are mainly used to characterise 1D subsoil models. This is done exploiting the data redundancy of the ground roll contained in seismic reflection or refraction data through a fully automatic processing procedure that allows to stack dispersion curves obtained from different records and retrieve experimental uncertainties. Hence the dataset to be inverted will be an ensemble of dispersion curves associated to a series of spatial coordinates along the seismic line. In this contest the use of Laterally Constrained Inversion (LCI) algorithm allows to manage such 2D effects in spite of the 1D model assumed for the forward problem solution. Different test have been conducted on different dataset for two synthetic models to evaluate the effects of the processing parameters, of the presence of noise and of lacks of information on the inversion results. All these effects have been observed applying lateral constraints of different strength during the inversion process.
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Joint Inversion of Seismic Data by Means of Multi-objective Evolutionary Algorithms
Authors G. Dal Moro and M. PipanAny sort of data is able to cast light only onto a specific aspect of the investigated problem. The implementation of a joint inversion scheme is meant to proficiently integrate the information that can be extracted from one dataset with those coming from another one. If the two objectives depend upon the same variables we can obtain a better-focused solution, while if the two objectives pertain (even just partially) to different variables thus their joint use can lead to new considerations characterized by a higher so-to-speak added value. The proposed computational scheme allows the joint inversion of non-commensurable datasets by means of analysis of the Pareto front performed in the framework of a Multi-Objective Evolutionary Algorithm (MOEA). The adopted approach also allows the validation of the provisional interpretation. In fact, Pareto front symmetry proves to be a valuable tool to verify the coherency of the adopted interpretation as an incorrect number of layers, reflector/refractor attribution or assumed Poisson values determine non-symmetric Pareto front as well as a wider model distribution in the objective space.
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GPR Rock Mass Imaging and Characterization by Attenuation Analysis
More LessWe apply Ground Penetrating Radar (GPR) to evaluate rock characteristics of interest in geological, geomechanical, hydrogeological, engineering and environmental studies. Primary objective of the study is 3-D imaging and detailed reconstruction of the electromagnetic velocity and attenuation field to define rock volumes that can be considered homogeneous from the geological and geomechanical point of view. The study is based on a series of experiments carried out in two test sites: a limestone quarry (test site-1) and limestone/dolomite contacts (test site-2). Rock mass characterization is performed by linking rock mass properties that can be estimated from GPR data to petrophysical properties (e.g. porosity, fluid content, permeability) and to rock characteristics such as texture, density of fractures and filling materials.
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Audio- and Radiomagnetotelluric Investigations of the Area of Railway Tunnel Route
Authors A. K. Saraev, M. I. Pertel and O. M. ProkofjevResults of audiomagnetotelluric (AMT) and radiomagnetotelluric (RMT) methods at the area of construction of the San-Pedro tunnel of the high-speed railway Madrid - Vayadolid are considered. Estimations of possibilities of used methods at study of deep structure of the area and detail mapping of rocks at the top part of cross section are fulfilled. A comparison of obtained results with data of previous investigations and drilling is carried out.
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Multi-disciplinary Approach for the Instability Analisis of a Down-town Site - Case Study
Authors L. Orlando and E. OlivetiThe paper treats the multi-disciplinary approach for the evaluation of instability of a down-town site using topographic monitoring, geological data, boreholes, electrical tomography and seismic refraction and reflection surveys. The latter was performed acquiring P and SH components.
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