- Home
- Conferences
- Conference Proceedings
- Conferences
74th EAGE Conference and Exhibition incorporating EUROPEC 2012
- Conference date: 04 Jun 2012 - 07 Jun 2012
- Location: Copenhagen, Denmark
- ISBN: 978-90-73834-27-9
- Published: 04 June 2012
201 - 300 of 948 results
-
-
The Barents Sea - Back in Business
Authors G. B. Larssen, H. M. Bjørnseth, O. S. Kløvjan, K. Kåsli, A. Ryseth, K. Rønning, A. Stoupakova, I. Laursen and K. SollidTectonically the Central Barents Sea is situated between sag basins in the east and a rift dominated terrain in the west. By merging geological data on both sides of the Russian-Norwegian borderline, a model for a working reservoir, hydrocarbon source rocks system and traps are indicated. Palaeogeographic and tectonostratigraphic considerations show that the distribution of reservoirs and hydrocarbon source rocks from the Late Palaeozoic to the Late Tertiary can be related to four main tectonic phases.
-
-
-
3D Fault Evolution in Oblique Convergent Strike-slip Fault Deformation
Authors B. Sapiie and M. HadianaOblique convergent strike-slip fault deformation has unique characteristic where both shortening and shearing acted simultaneously to form simple shear type deformation. Faults development consist of several different types with various style, pattern and geometry. However, previous study indicated that fault pattern and behavior were varies significantly in many cases. The main purpose of this paper is to demonstrate application of analogue sandbox modeling in solving problems in reconstructing basin with this complex deformation. The comparison with natural examples will be discussed for several basins from Western and Eastern Indonesia. There are several differences and similarities in terms of styles and total number of faults occurred in Case 1, 2 and 3. The comparison results suggest several major conclusion concerning roles of modelling variables such as experimental materials (sand, gypsum or both) and basement configuration both geometry and positioning. It has been demonstrated by several sensitivity tests, those variables above were highly influenced in controlling detailed internal deformation. Variability in layering materials (rheology), will generate more complex internal deformation. The main big difference between the two materials is mainly on structural styles which heterogeneous materials exhibit more faults and fold-related-folds. Several thrust-fault duplexes are formed in higher shortening in heterogeneous setting.
-
-
-
Developing a New Algorithm for Calculating Fault Seals Within the Structural Model
Authors P. Røe, H. Kjønsberg and C. OftebroTraditionally fault seal calculations take place directly within the simulation grid. This approach works well for grids where all the faults are aligned along the grid pillars, but implementing an algorithm that works with stair-stepped representation of the faults has proven to be very difficult. Especially the calculation of the displacement field used both indirectly in the fault seal parameter calculation and directly in the calculation of fault zone permeability is challenging. It is hard to find where the different grid layers intersect the fault trace, and the layers are not always completely represented on both sides of the fault. We present a novel algorithm where the calculation of the fault zone permeability is carried out on a 2D plane representing the fault surface. The input parameters needed for calculating the fault zone permeability are resampled from the simulation grid onto the 2D plane, while the resulting fault zone permeability is resampled back into the simulation grid, prior to calculation of the fault transmissibility. The new approach is shown to generate good results both for pillar-faulted grids, and for grids with stair-stepped faults, and also works well near complex truncations.
-
-
-
Relationship between Structure and Stress Field - A Key for Successful HC Exploration in the Northern Zagros Thrust Belt
Authors F. Arboit, R. Di Cuia, A. Riva and R. BitonteThis study has focused on the fold trains part of Iraq which lies north of Latitude 35 North, and they involve Cretaceous to Cenozoic sediments. These sediments consists mainly of limestone, dolomites, sandstone, claystone and conglomerates. It appears quite clear that the different mechanical competence of the lithologies involved during the folding control the style and the geometries of the investigated structures; the alternation of competent (laminated and massive dolomite and limestone) and incompetent (claystone, siltstone and shale) is easy detectable in structures as the Bina Bawi, Shaikan, Safeen anticline, with the heavy eroded incompetent lithologies (Kolosh and Gercus formations) among the competent limestone of the Pila Spi and Aqra Bekhme formations. . The interpretation is based on the integration of the available geological and geophysical subsurface data, stratigraphy and tectonic published information, present day stress field measurements and a new structural interpretation based on remote sensing techniques for all the anticlines in the high folded zone. The results highlight a very complex structural situation due both to the stress distribution and portioning (from Cretaceous to Neogene) and also to the sedimentological evolution.
-
-
-
The Upper Jurassic - Lowermost Cretaceous Source Rocks in the Central Graben, North Sea - Status and Future Challenges
Authors H. I. Petersen, A. C. Holme, M. F. Whitaker, C. Andersen, H. P. Nytoft and E. ThomsenThe principal source rocks in the Danish and southern Norwegian Central Graben in the North Sea are the Upper Jurassic to lowermost Cretaceous marine shales of the Farsund Formation that corresponds to the Kimmeridge Clay Formation and equivalents elsewhere in the North Sea. The evaluation of the Farsund Formation shales shows that the distribution of the generation potential and the maturity is more complex than generally accepted. Further studies are required to understand the variations in source rock quality, the controlling factor(s) on kerogen composition, and to determine if the rich intervals can be regionally correlated. The Upper Jurassic marine shales underlying (Lola and Haugesund Formations) the Farsund Formation are traditionally not included as potential source rocks, but the documented extra potential of the Upper Jurassic shales below the Farsund Formation should be investigated in more detail. Attention should also be given to deeply buried mature source rocks in areas with overpressure. These factors have considerable impact on location and extent of kitchen areas. The problems are explored with the goal to capture new knowledge of the Upper Jurassic petroleum source rocks.
-
-
-
Petroleum System of the Palaeozoic - Mesozoic Strata in the Basement of Central Part of the Polish Carpathians
Authors M. Wróbel, D. Więcław, P. Kosakowski and M. J. KotarbaThe geochemical characteristic of the Palaeozoic - Mesozoic strata in the cross-border of the Upper Silesian and Małopolska blocks in the basement of the Polish Carpathians determined the Devonian and Carboniferous source rocks as the best source for hydrocarbon generation. The oil-condensate-source rocks correlations indicated the source of the Łąkta gas field and the Grobla oil field. The maturity modelling revealed that the Devonian source rocks reached a late phase of “oil window”, and locally ”gas window”. The Carboniferous source rock was mature enough to start the generation processes. The generation started in the late Carboniferous, but the main phase of the petroleum processes took place in Paleogene and Neogene. The expulsion was observed only in the Devonian source rocks. Vertical migration by fault system in both blocks mainly during Neogene resulted in oil and gas accumulation in the Upper Jurassic carbonates and Upper Cretaceous sandstones. The petroleum modelling indicated the Devonian source for oil and gas fields in the study area. However, condensate-source rock correlation also suggests the presence of the Carpathian flysch source for hydrocarbons accumulated in the Łąkta field.
-
-
-
Revisited Exploration Potentials in the Area between Sicily, Tunisia and Malta
Authors A. Riva, M. Marian, S. Borello and R. Di CuiaThe triangle among Sicily, Malta and Tunisia is an area where hydrocarbon exploration has been very intense during the last 50 years. The water depth is reaching more than 1400 meters in the Pantelleria Graben, while in the Malta and Medina grabens the water depth reaches more than of 1200 meters. The maritime state boundaries in some cases are still uncertain, with disputed waters especially around Malta, with Italy and Libya claiming some parts of the Maltese waters. Over the entire area of the Sicily and Malta Channels, the previous exploration activity has proved the presence of at least five different play types, mainly working in the offshore of Sicily and Tunisia/Libya. The extensive exploration, however, did not cover some portion of the Linosa and Malta grabens, including the associated horsts, that were open to exploration in 2010. Here, due to the distribution of mesozoic source rocks, some structural traps can develop. Another interesting area is represented by the submerged inner portion of the Maghrebian-Sicilian Thrust Belt: the amount of direct geological informations is low and there are no clear hydrocarbon systems. The lattest is an area where real frontier exploration can occur, with difficult geology.
-
-
-
Application of the Oil Maturity Data to Migration and Reservoir Infill in the Low Kura Depression, South Caspian Basin
By D. HuseynovAccording to regional and local features of isotopic-geochemical parameters of the South Caspian oils, in the Lower Kura depression the fluid migration occurred from local sources confined to Mugan-Salyan and Kursanga troughs.
-
-
-
Late Paleogene Submarine Fans in Baffin Bay and North-West Greenland
Authors P. C. Knutz, U. G. Gregersen and J. R. HopperResults from seismic mapping on the NW Greenland margin and Baffin Bay demonstrates the presence of submarine fan lobes formed in elongate graben and rift basins. Fan deposition commenced during late Eocene and possibly into Oligocene, presumably as a consequence of major tectonic activity in the source region, linked to the Eurekan Orogeny. The largest of the fan lobes extends for more than 300 km through the Melville Bay Graben and attains thickness up to about 1.3 km below the main boundary fault. Seismic geometries displaying elements of channels and central mounds, points to sand transport through the graben axis and hence a strong potential for reservoir development. On the Greenland shelf margin the lobes are generally located at burial depths between 1.5 and 4 km favorable for petroleum maturation and exploration.
-
-
-
Structural Provinces and Suggested Key Play Factors Offshore West Greenland
Authors S. M. Knutsen, N. P. Arendt, J. Stilling, M. K. Runge and M. P. BrandtThe offshore West Greenland is tentatively categorized into four structural provinces from S to N: Cape Farewell, Nuuk West, Disko West and Baffin Bay. The delineation of the provinces are based on differences in post rift evolution, mainly timing and nature of i) structuring, some areas dominated by extension while other being influenced by transpression / transtension, ii) uplift / subsidence, possible exhumation and especially Neogene sediment input, and iii) volcanic / magmatic activity. The variations in geologic post rift histories suggest that different play factors should be sought mitigated in this early exploration phase in Greenland. Caution is suggested for the use of analogues and play evaluations across the provinces without adjusting for the tectonic and structural differences.
-
-
-
Phoenix Prospect - Haltenbanken, Norway - Derisking of a Large Undrilled BCU Closure through Improved Imaging
Authors L. Ben-Brahim, P. Melas, K. Spetz, J. Suiter and J. P. MathieuThe Halten Terrace offshore Norway is a prolific but mature petroleum province. It is mostly a Jurassic play basin with conventional tilted blocks and salt induced features. The search for remaining hydrocarbons relies on new concepts and technologies. Seismic imaging is one of the critical tools to unravel complex or subtle traps. Total Norge has a 100% interest in blocks 6406/7 & 8. The main prospect (Phoenix) is a truncation trap updip from well 6406/8-1. It is associated to a large closure at BCU level, often a favorable factor for trapping hydrocarbons. Main objectives are the Lower to Middle Jurassic shoreface reservoirs of the Ile and Tilje formations. Additional plays are evaluated at Upper Jurassic and Lower Cretaceous levels. A 3D seismic dataset was reprocessed through time and depth workflows. As a result, seismic imaging has been substantially improved. This improvement is seen also pre-stack and will enable to investigate attributes such as AVO. An integration of regional basin modeling and pressure cells study enabled to assess sourcing and seal issues. This information together with a quality seismic dataset led to an improved evaluation of risks and stakes for this large prospective structure.
-
-
-
Jurassic Sandstone Plays in the Danish Central Graben, North Sea - New Results
Authors P. N. Johannessen, C. Andersen, K. Dybkjr, F. Jakobsen, L. Kristensen, R. Weibel, H. I. Petersen, E. Thomsen and E. B. NielsenRecent exploration activities have led to encouraging results in Jurassic – Lower Cretaceous sandstones in the Danish Central Graben. Two Upper Kimmeridgian High-Temperature High-Pressure (HTHP) environment sandstone plays have been investigated. 1) The Hejre wells located in the Gertrud Graben found oil in the Upper Jurassic shallow marine shoreface sandstones at a depth below 5000 m. 2) The Svane-1 well located in the northern part of the Tail End Graben found gas-bearing sandstone successions of deep marine gravity-flow origin below 5300 m. Further, a number of wells drilled within the most recent years adjacent to existing Jurassic discoveries all encounter hydrocarbons in Middle or Upper Jurassic sandstones. The good porosity on the HTHP sandstone plays is linked to dissolution of feldspar grains and to thick pore-lining illite coatings which inhibit quartz precipitation. Upper Jurassic shallow and deep marine sandstones are sourced from the prolific claystones of the Farsund Formation; Middle Jurassic fluvial-deltaic sandstones are sourced from interbedded coals and coaly claystones. The future challenge is to predict the distribution of sandstones that have undergone a favourable diagenetic development. The focus in this review will be on distribution and quality of sandstone reservoirs.
-
-
-
The First Results of Continuous Passive Surface Seismic Monitoring at the CO2 Injection Site of Ketzin
Authors D. Santonico, X. Zhang, A. R. Verdel, J. A. C. Meekes and R. J. ArtsSince July 2008 CO2 is injected into a saline aquifer near Ketzin, in Germany. The reservoir used for CO2 injection is the Stuttgart Formation of Triassic age, located at a depth of about 650 m. Close to the injection well, TNO designed and implemented a permanent shallow seismic monitoring system. The system consists of 3C-geophones and hydrophones at locations along a line of 130 meters and at depths up to 50 meters. Since September 2009 up to date the array has recorded passive seismic data continuously. A procedure has been developed to automatically detect and locate very low magnitude seismic events. This paper describes the first results, including a calibration test with a known surface source, where two months data have been investigated in detail. Over 20.000 seismic events were detected automatically during this period, of which the 200 strongest ones were analyzed in more detail. Localization of these 200 events learned, that more than 99% originate from a single location at the surface, most likely related to industrial activity. Much weaker events originating from the subsurface have been observed as well. Interpretation and localization of these events is ongoing.
-
-
-
Correlation Detection and Location for Microseismic Events Induced by Hydraulic Fracturing
Authors R. Cieplicki, L. Eisner and D. AbbottWe develop methodology of correlation detection and relative location for microseismic events induced by hydraulic fracturing. Specifically we apply the methodology to surface recording by cross-correlating strong (master) events to detect weak events (slaves). Furthermore, we show how real events with weak signal can be detected in the presence of high surface noise. We also locate detected events relative to master by stacking of cross-correlations along differential moveouts. We show methodology to select representative master events suitable for hydraulic fracturing induced seismicity. We apply this methodology to hydraulic fracturing data and detect similar number and consistent locations of microseismic events as we obtained with direct location technique.
-
-
-
The Importance of Coupling Passive and Active Seismic Methods in Geothermal Fields - A Case Study at Paralana, Australia
Authors J. Albaric, N. Langet, M. Hasting, I. Lecomte, V. Oye, K. Iranpour, M. Messellier, E. M. Llanos and P. ReidThe Paralana Enhanced Geothermal System is situated in South Australia and is a promising project aiming to exploit natural heating from the radiogenic basement. A 5-day stimulation of the well, in July 2011, induced more than 7000 microearthquakes. Seismic event waveforms are complex, exhibiting a high amplitude seismic phase arrival between direct-P and direct-S waves, a phase which complicates event analyses and needs to be explained. In such projects, site characterization should use all available data, a key issue being a proper knowledge of both P- and S-velocity models. In the present case, a combination of active and passive seismic data, acquired before and/or during hydraulic fracturing, was paramount to the definition of a proper model. Using existing 2D seismic profile interpretations and a seismic log, and applying ray tracing to constrain interval velocities, a 3D velocity model was built in order to improve the event locations. Furthermore, to define the origin of the unknown phase, 3D ray-tracing modeling was systematically applied to test different scenarios. Actual results show that in term of arrival time, these phases most likely correspond to converted waves on interfaces between 1.6- and 2.5-km depth rather than on nearby steep faults.
-
-
-
A Full-waveform, Migration-based Deconvolution Approach to Locating Micro-seismic Events
Authors J. B. U. Haldorsen, M. Milenkovic, N. Brooks, C. Crowell and M. B. FarmaniWe present a new approach to generating 3D location maps for micro-seismic events from 3-component data. The method combines full-waveform vector migration with an imaging condition based on semblance-weighted deconvolution. The semblance-weighted deconvolution keys in on the signal-to-noise conditions of the data to give a high-resolution, low-noise estimate of the locations for the micro-seimic sources. As the method requires no explicit time picking or event association, it is well suited to be run as an either fully-automated or a semi-automated process. Almost as a by-product, the method provides a natural measure of the uncertainty associated with the locations of the individual micro-earthquakes.
-
-
-
Shear-tensile / Implosion Source Model vs. Moment Tensor - Benefit in Single-azimuth Monitoring, Cotton Valley Set-up
By J. SilenyMoment tensor (MT) has become a standard for description of seismic sources, both in earthquake seismology and for various types of induced seismicity. It is a general dipole source, but for practice it may be too general, its generality causing troubles during its reconstruction from noisy data in the inverse process, which may be additionally ill-conditioned due to inexact hypocenter location or availability of a rough velocity/attenuation model only. Then, the retrieved source may be biased. It seems reasonable to assume a simpler source model directly describing the physical phenomena anticipated in the particular focus. A simple combination of a shear slip with tensile crack or 1D implosion (STI) may be a good model both for natural earthquakes and induced events. The model simplification introduced is crucial in cases of depleted sensor configuration when the moment tensor fails, in single-azimuth monitoring in particular. This is just the case of application in oil and gas industry, where the monitoring of seismicity induced by hydrofracturing is typically performed from single monitoring borehole. Then, MT is able to provide constrained solutions only (e.g. deviatoric), but STI detects also non-shear component correctly, providing important information on increase of permeability of the reservoir.
-
-
-
Samples of Hot Dry Rock Soultz Injection Micro-earthquakes - Mechanism Using Alternative Source Models
Authors Z. Jechumtálová and J. ŠílenýThe geothermal reservoir at Soultz-sous-Forêts is a valuable natural laboratory for understanding the mechanisms of the micro-earthquakes generated during stimulations and circulation tests. There is an ongoing effort towards the retrieval of the mechanisms though the indication of the type of fracturing of the rock massif still remains ambiguous. Recent studies indicate prevailingly shear slip but rarely there is also observed a non-shear pattern. Moment tensor – used today as a universal tool for description of the mechanism – captures general balanced dipole sources. However, for practice it may be too general as it may include also non-physical sources. Opening new fractures can be described in the first approximation by a tensile crack, optionally combined with a shear slip. We call this alternative model a shear-tensile/implosion source model. From the bulk of the seismicity recorded during stimulation in 2003, we concentrated on the first phase of the injection when only a single borehole in the site was stimulated. We processed thirteen micro-earthquakes with magnitudes bigger than 1.4 and not processed previously. We found that again their source mechanisms were dominantly pure shear on pre-existing faults just as the stronger micro-earthquakes. They are also in agreement with the stress pattern from in-situ measurements.
-
-
-
Statistical Evaluation for Comparative Microseismic Interpretation
More LessMicroseismic monitoring is often used to evaluate differences in hydraulic fracturing, resulting from either changes in the stimulation or geologic setting. Often the various microseismic images of individual fracs are each separately interpreted for fracture geometry or activity rates, and then these absolute interpretations of the various fracs are compared. However, comparisons can be made between variations in specific fracture dimensions in each image, including using statistical tests to quantify significance of relative differences. Such a relative comparative interpretation is more robust and relies on a simpler assessment of the location uncertainty in contrast to the need to consider all aspects of location accuracy for absolute interpretations. Microseismic activity rates can also be compared to quantify the relative seismic deformation. The resulting comparative microseismic interpretation can be used as part of a comparative hydraulic fracture evaluation to test the response to different designs and ultimately optimize the stimulation.
-
-
-
Towards Using Seismic Moment Tensor Inversions to Infer Reservoir Rock Properties
Authors A. M. Baig and T. I. UrbancicHydraulic fracturing of low-permeability formations enhances the reservoir drainage characteristics through the creation of a discrete fracture network, propped open with sand or other proppants. Ductile formations are thought to generate more linear fracture geometries compared to more brittle formations favourable to the creation of a complex and interconnected discrete fracture network. Brittleness in a formation is largely controlled by Poisson’s ratio, with lower numbers being considered more brittle. Variations in this quantity throughout the reservoir have been invoked to explain variations in microseismic activity observed in treatments with a strong event asymmetry or complicated geometries. Seismic moment tensor inversion is a method that is being increasingly used to characterize the microseismic events recorded during such stimulations. By back-projecting the microseismic signals recorded across a number of different azimuths to the event’s source, the failure mechanism representing that source may be attained. These mechanism determine the style of failure as well as the geometry of the failure plane allowing for the determination of the dominant fracture sets that a treatment is activating and the degrees of connectivity shown in the dataset. These fracture sets can provide constraints on the rock properties controlling the growth of these fractures in the reservoir.
-
-
-
Lithostatic Stress Driving Changes on Fracture Aspect Ratio - Ultrasonic Experiment and Results
Authors P. E. P. Marcondes, J. J. S. de Figueiredo, J. Schleicher, N. Dayur and R. R. StewartElastic anisotropy due to aligned cracks has been the subject of many seismic physical modeling experiments. In this paper we present a physical study of the aspect ratio as a function of applied uniaxial stress. We carried out pulse transmission measurements of P- and S-wave velocties in a reference model without inclusions and in a model with penny-shaped neoprene inclusions. The reference model is an anisotropic matrix that consists of stacked plexiglass plates. Rubber discs were used as inclusions in that anisotropic matrix leading to secondary anisotropy. We recorded ultrasonic seismic data using P-wave transducers with central frequency 120 kHz and S-wave transducers with 90 kHz. We compressed the physical models using pressures ranging from 3 to 15.8 MPa. Full crack closure occurs at stress 14.6 MPa normal to model faces. Our analysis indicates three different regimens for the behavior of the inclusions. These results suggest a different %dependence of the crack aspect ratio on uniaxial tress at the low state of stress than usually described in the literature. Though our results are not extensive, they show that simple experimental approaches might provide valuable insight into the behavior of cracked rocks at reservoir stress levels.
-
-
-
Fracture Network Growth for Prediction of Fracture Characteristics and Connectivity in Tight Reservoir Rocks
Authors A. Barnhoorn and S. F. CoxFracturing experiments on very low-porosity dolomite rocks shows a difference in growth of fracture networks by stress-driven fracturing and fluid-driven fracturing. Stress-driven fracture growth, in the absence of fluid pressure, initially forms fractures randomly throughout the rocks followed by growth and coalescence of fractures to form a connected fracture network. Fluid-driven fracture growth is represented by preferential fracture growth occurring initially at the high fluid pressure part of the rock. With prolonged durations of high fluid pressure at the tip of the newly formed fractures, the network propagates rapidly through the sample and away from the high fl uid pressure reservoir. This difference in fracture network growth and the differences in fracture statistics between both scenarios have important control on the flow of hydrocarbons in fractured reservoirs and thus on hydrocarbon productivity. Differences in fracture statistics can eventually be used as improved input into reservoir and production models. 3D X-ray tomography analyes of a fractured specimen show very early 3D fracture connectivity, much earlier than depicted from conventional 2D analyses. The early 3D connectivity of fractures and enhanced permeability may also be critical to the understanding of hydrocarbon storage and migration or seal integrity.
-
-
-
Conditioning of Geomechanical Simulations to Well Data in a Fractured Carbonate Reservoir
By A. D. IrvingConditioning of spatial explicative variables, or "drivers”, to well data is an important step in validating fractured reservoir models and increasing confidence in their utilisation for reservoir management. A case study is presented of a carbonate reservoir in which fracture orientations and frequencies output from geomechanical simulations are conditioned to distributions interpreted from well data. The distribution of fault-related elastic stress is simulated by imposing a palaeostress field on the interpreted structural framework. Orientation of shear and tensile fractures is output along with the distance to failure according to a combined tensile and shear failure criterion. These are compared with fractures interpreted from borehole image logs, which allows rejection or modification of some possible hypotheses for fault geometries and palaeostress. Once a satisfactory match is obtained, the simulated failure criterion is combined with other drivers in a multivariate analysis to produce a three dimensional fracture probability model which explains over three quarters of the observed variation. The resulting property can be used as input to karst modelling and subsequent reservoir simulation.
-
-
-
A Method for Producing Photorealistic Digital Outcrop Models
Authors P. Arbués, D. García-Sellés, P. Granado, M. López-Blanco and J. A. MuñozOutcrop studies can be substantially improved by use of photorealistic digital outcrop models. A method is presented that has been tested for decametre to hectometre long outcrops. The models have accuracy and resolution around one decimeter and the models are conveniently scaled and oriented, allowing for comparison to geological data that were directly acquired in the field. The gear involved is lightweight and low cost when compared to LIDAR. The geologist can backpack this gear, decide acquisition on the flight, and finish the computer processing back in the base camp or in the office. The experiments have been carried in a series of Spanish outcrops that represent a variety of depositional settings: alluvial fan, fluvial fan, point bar deposits, fan-delta, and deepwater. The output models will be discussed in in terms of their quality by report to LIDAR data.
-
-
-
3D Structural Model of a Cretaceous Carbonate Sequence - Lessons Learned for Reservoir Modeling
Authors R. Di Cuia, R. Bitonte, G. Rizzo, E. Tondi and A. RivaWe have selected a deep and large quarry cut in the upper cretaceous fractured limestone of the Apulian Platform to study the structural features at different scales and to model the structural network in 3D using a multiple steps approach in order to understand the impact of the data input and the different modelling techniques used on the final 3D structural model
-
-
-
Interaction between Downslope and Alongslope Processes on the Margins of Daihai Lake, Northern China
More LessDaihai Lake, a modern lacustrine rift basin, located in the Inner Mongolia, Northern China, serves as an important modern analog for understanding deltaic depositional processes in an active rift setting. Two of the deltas (Yuanzigou delta and Bulianghe delta) on the margins of Daihai Lake were surveyed to compare and contrast stacking patterns using aerial photographs, field trenching and sediment sampling. Shallow cores and trenches data collected from the margins of Daihai Lake indicate that a variety of depositional processes have been active since Daihai Lake formed. Two 3-D sedimentation models which employ chronostratigraphic correlation technique were generated. The chronostratigraphic sedimentation models predict and represent the architectures and sand-body continuity of sediments. Stratigraphical coincidence of the broad sheeted drifts and channel erosion suggests a coupling between downslope and alongslope processes. This study provides an insight into the architecture of complex sedimentary facies associated with highlights key differences between downslope flows and alongslope currents. The distribution of sand within these deltas is of particular interests, with applications in understanding the architecture of hydrocarbon reservoirs formed in lacustrine rift basin.
-
-
-
Integrated Workflow for Consistent Model Building from Depth Conversion to Flow Simulation - North Sea Field Case
Authors J. A. Skjervheim, X. van Lanen, D. Hulme, V. Røine Stenerud, E. Zachariassen, S. Liu, J. Hove and G. EvensenTo enable a consistent model chain from depth conversion to flow simulation, an integrated approach to reservoir modeling is required. The objective of our work has been to develop and demonstrate an integrated work flow, where the following models steps are involved; structural modeling, building of the geological and simulation grids, facies and petrophysical modeling, up-scaling, segmentation, well modeling, flow simulation, and seismic forward modeling. The basic idea is to have a model chain which is updateable, consistent, and repeatable. In our integrated model work flow, model updating and uncertainty modeling are treated as an integrated process. The essential concept is that the uncertainty is represented by an ensemble of realizations that are updateable. The modeling work flow is developed and demonstrated on a structural complex North Sea full field application. Especially, we have focused on the structural model building; i.e. how to make it fast and updateable, and how to include uncertainties.
-
-
-
A Strategy for Effective Local Updates of the Geological Structure in an Earth Model during Drilling
Authors E. Suter, E. Cayeux, A. Escalona, T. Kårstad and E. H. VefringThe increased amount of subsurface measurements available in real-time while drilling with wired pipe opens new possibilities for optimisation of well placement. The continuous stream of new information reduces uncertainty and allows revisions of the geological interpretations made prior to the drilling operation. When the most current and precise knowledge is required and the time available to update the earth model is limited, methods that support effective, local model modifications are essential. We demonstrate a strategy where grids are replaced by flexible geometrical transformations. It allows separate management of geological structure and spatial petrophysical properties. The transformations enable effective structural modifications in an earth model without compromising existing representations of petrophysical properties. Principles of the methodology are exemplified by demonstrating automatic insertion of new faults and pinch-in of new sedimentary layers. The modifications are based on information received during the drilling process, where geological markers interpreted during the operation constrain the alterations.
-
-
-
A Data-restoration and Model-reconstruction Workflow for Simultaneous Seismic Interpretation and Model Building
Authors S. A. Petersen, . Hjelle, S. Hustoft, M. Houbiers and R. RasmussenA workflow for simultaneous seismic interpretation and model building is presented. The workflow consists of two sequences. A first, in which a depth seismic section is gradually altered, by reverse and mainly structural processes, in order to restore the seismic section of the target to the time of deposition. In the second sequence a distribution of properties representing the target becomes subject to the normal version of the previous reverse geological processes, now ordered forward in time. The final property distribution is the reconstruction of the present day distribution. The method has many interesting advantages compared to present day workflows. It is fast and the model becomes geologically feasible. During the successive data-Restoration the impact of faults, deformation and compaction is gradually removed by invoking the inverse of these processes. The section looks “younger” and e.g. stratigraphic interfaces appears easier to interpret. Fewer - 10 times less than normal - and simpler surfaces are needed to represent the target, no matter how much it was compartmentalized originally. Having the restoration processes and their order in place the model-Reconstruction is done very fast executing the normal processes forwardly. Additional, mainly depositional and erosional processes can be added during reconstruction.
-
-
-
Aptian Relative Sea-level History of the Northern Maestrat Basin, E Iberia
Authors T. Bover-Arnal, R. Salas, J. Guimer and J. A. Moreno-BedmarTwo stages of forced regression of relative sea-level can be recognized in the Aptian carbonate sedimentary succession of the northern Maestrat Basin (E Iberia). The first forced regressive episode occurred during the late Early Aptian and is distinguished by the presence of platform-detached bioclastic shoreface wedges, which display hydrodynamic sedimentary structures. The second phase of forced regression has a Late Aptian age and is characterized by an erosional incision, which cuts platform carbonates down to about 90 meters. This incision is filled by peritidal marls and carbonates that were deposited during the following transgression. The relative sea-level changes recognized had a glacio-eustatic magnitude and have been recognized in other basins worldwide.
-
-
-
Characteristics of the West Greenland Margin in the Southern Baffin Bay
Authors M. Block, V. Damm, A. Ehrhardt, K. Berglar, M. Schnabel and T. AltenberndFor reliable hydrocarbon assessment of the West Greenland margin information about the structural inventory including the location of the continent ocean boundary is of special importance. There is still no consensus about the nature of the underlying crust in central Baffin Bay. A new multichannel seismic traverse extending from the outer shelf of the south-eastern Baffin Bay into the deep sea area is presented and discussed. The most spectacular features along the traverse are the flood basalts extending into the deep Baffin Bay, the about 30 km wide wedge of seaward dipping reflectors (SDR’s), and the well recognizable breakup unconformity. These features indicate clearly that oceanic crust exists in the deep Baffin Bay and that Greenland’s continental margin in the south-eastern Baffin Bay is a volcanic passive margin. The continent-ocean transition (COT) could be determined at the seaward termination of the wedge of SDR’s. From the fact that the rifting phase was ongoing after the extrusion of the flood basalts it is deduced, that the beginning of the drift phase and thus the onset of seafloor spreading is younger than the flood basalts. It is proposed that in the southern Baffin Bay seafloor spreading started in the Early Eocene.
-
-
-
Analysing Magnetic Components of Samples from Svalbard
More LessThree core specimens from a Triassic interval in Core LYB_CO2_DH4 were oriented palaeomagnetically and a primary Triassic reverse direction determined corresponding to the early Carnian. The magnetic mineral is High-Titanium magnetite indicating the Siberian region LIP rocks as source area. A Cretaceous pTRM is present, which is caused by a thermal event with increased temperature of 250-300C in Early Cretaceous or Late Jurassic. Three oriented outcrop samples from the Cretaceous Albian were also analysed. They did not contain any pTRM and it was thus concluded that the pTRM in the Triassic core is pre-Albian.
-
-
-
Influence of Sediments Consolidation on Predicting P-wave Sonic Log Measurements
More LessIn old exploration areas, a fundamental well log measurement may be absent in the interpretation process. Empirical formulas are generally applied in the estimation of the missing log measurements. However, models based on physical concepts are preferred, as they can be used in sedimentary basins elsewhere. In this work, we present a petrophysical model for describing P-wave sonic slownesses in unconsolidated and consolidated clastic formations. The proposed model is product of algebraic manipulation of a published density model, incorporating a compaction factor which allows for effects of sediments consolidation. Results of an experiment using required log measurements through a turbiditic formation confirms the reliability of the petrophysical model in estimating sonic slownesses.
-
-
-
Tight Precambrian and Paleozoic Reservoirs in the Light of Petrophysical Analysis
Authors J. A. Jarzyna, P. I. Krakowska and E. PuskarczykStandard laboratory investigations turned out to be not sufficient for the Precambrian and Paleozoic rocks from great depths. Especially low porosity and permeability were difficult to be accurately determined. Combination of several known methods as: NMR investigations and mercury porosimetry and micro-tomography (micro-CT) showed new aspects in investigations of such rocks, important as tight gas reservoirs. Improved methodology in NMR processing by detailed cut off determination enabled more precise Free Fluid Index determination. Computerized mercury porosimetry results visualization and processing provide new utility value as automatically determined Swanson parameter correlated with petrophysical properties. Micro-CT enriched the image of porous space in qualitative and quantitative ways.
-
-
-
Elastic Properties of Lochaline Sandstone - Numerical Experiment vs. Measurements
Authors M. Pervukhina, V. Shulakova, M. Lebedev, S. Mayo, M. B. Clennell and B. GurevichP- and S- velocities of clean quartz Lochaline sandstone are numerically simulated using microtomographic images with resolution of 2 micron and compared with the velocities measured at ultrasonic frequencies. The numerically simulated velocities are in a good agreement with velocities measured at confining pressure of about 30-40 MPa which is high enough to close soft pores but do not cause noticeable deformation of equant pores yet. The obtained results shows that while effects of soft porosity on elastic properties of sandstones cannot be directly simulated from microtomograms, such simulation give reliable results when soft pores are closed.
-
-
-
Change of Static and Dynamic Elastic Properties due to CO2 Injection in North Sea Chalk
Authors M. M. Alam, M. L. Hjuler, H. F. Christensen and I. L. FabriciusReservoir modeling and monitoring uses dynamic data for predicting and determining static changes. Dynamic data are achieved from the propagation velocity of elastic waves in rock while static data are obtained from the mechanical deformation. Reservoir simulation and monitoring are particularly important in enhanced oil recovery by CO2 injection (CO2-EOR) in chalk as, chalk reservoirs are vulnerable to compaction under changed stress and pore fluid. From South Arne field, North Sea, we used Ekofisk Formation chalk having approximately 20% non-carbonate and Tor Formation chalk having less than 5% non-carbonate. We studied difference in static and dynamic behavior. Furthermore, brine saturated data were compared with CO2 injected data to reveal the effect of supercritical CO2 injection in both static and dynamic elastic properties. We used strain gauges and LVDTs to measure static deformation. We observed lower dynamic elastic modulus for chalk with higher non-carbonate content at porosities lower than 30%. In 30% porosity chalk, dynamic compressional and bulk modulus were found significantly higher than the static modulus. Static measurements with LVDT were found lowest. The effect of CO2 injection was notable in dynamic elastic properties, while a possible change in static elastic properties was below detection limit.
-
-
-
Xu and White Revisited
Authors M. Sams, T. J. Focht and N. Azuairi Che SidikThe Xu and White method for modelling the elastic properties of sand and clay mixtures has proven popular and effective. The method assumes that the aspect ratio of the porosity associated with sand is different from that associated with clay, but that these values remain constant over large intervals. An improved prediction of the elastic properties can often be made by applying a single aspect ratio to the total porosity. Keeping the effective elastic properties of the sand and clay constant over large intervals, the optimal aspect ratio must vary with depth. The application of this method to a set of wells in an oil and gas reservoir suggests that these variations in optimal aspect ratio can be predicted from the petrophysical properties of the rocks. This relationship between aspect ratio and petrophysical properties can be used as an additional constraint to improve the quality of the petrophysical model in areas of borehole washout and to gain insight into the effects of hydrocarbons and invasion on the elastic properties of the reservoir rocks.
-
-
-
4D Close-the-loop Using Probabilistic Seismic Inversion on the Astokh Field, Offshore Sakhalin
Authors M. Kleemeyer, P. Gelderblom, A. Altintas and K. Foresteat will largely focus on improved oil recovery. To make optimal use of the 4D data, a 4D Close-the-Loop and assisted history matching project was initiated. Often 4D data is interpreted qualitatively only to obtain flushed areas. This paper shows a quantitative approach for 4D Close-the-Loop using 4D probabilistic seismic inversion in a complex geology setting, which results are subsequently used as input for a 4D assisted history matching. The probabilistic inversion, using Shell’s proprietary software XStream/Promise, based on the dynamic model combined with the rock model properties, can reveal the complex saturation changes and shows their lateral and vertical distribution, as well as their uncertainty.
-
-
-
Fluid Substitution and Production Effects Imaged for North Sea Oil Field from Quantitative Seismic & CSEM Interpretation
Authors J. P. Morten, D. Timko, P. A. Olsen, F. Roth, A. K. Nguyen and C. PacurarDedicated "Fluids and Fluid Flow" We have performed a quantitative, joint interpretation of 3D seismic and 3D CSEM data from the Troll Western Oil Province. The presented methodology results in 3D distributions of effective porosity and hydrocarbon saturation. The estimated reservoir property distributions demonstrate how the result of fluid flows due to production and gas injection can be imaged.
-
-
-
Seismic Reservoir Characterisation of a Channel Sand Oil and Gas Field, Malaysia
Authors T. J. Focht, M. Sams, D. Brookes and J. TingAn oil and gas field in the Malay Basin has been characterised through a deterministic seismic inversion. The sole reservoir of the field is a channel sand with gas and oil. Interpretation and inversion have been used in an iterative fashion to produce a deeper understanding of the field. Initial inversions have been interpreted in terms of channel sand and fluid distribution. A rock physics model has then been used to translate these into a low frequency model for further inversions. The interpretation is then updated. The rock physics understanding has also led to improvements in the seismic data. Conditioning the seismic gathers for anisotropic moveout increased the useable angle range from 40 to 55 degrees, which is important for this Class II AVO reservoir. The inversion based seismic reservoir characterisation has made significant changes to the original predictions of sand and fluid distribution that have so far been proven by the drilling of six additional wells.
-
-
-
Case Study on Field Scale Seismic Definition of the Upper Ordovician Reservoir Configuration, Murzuq Basin, South-West Libya
Authors R. M. Gruenwald, A. Ponte, N. McDougall and K. S. TawengiAs result of combined exploration efforts by REMSA S.A. as operator and OMV as partner several fields were discovered in the Murzuq Basin. 3D Q Seismic reflection datasets are used to unravel the complexity of reservoir-seal contacts of the Late Ordovician glacial deposits on a field scale. Three wells, apparently drilled within a four-way dip closure, targeting the Mamuniyat sandstone reservoir were studied to explain the unexpected lateral disconnection. As a result of detailed well and 3D seismic data integration, three hypotheses were evaluated to explain the limits of the structural closure. These include; the presence of a non reservoir barrier laterally separating the Upper Mamuniyat reservoir in wells A&C from well B, analyzed on a variance time slice close to the OWC, a low VRMS due to the presence of Bir Tlacsin, and detection of different generation Mamuniyat sandstone bodies based on VoxelGeo amplitude analysis. Geo-bodies of the Upper Ordovician depositional system were imaged on seismic on a regional scale, explaining the presence of different generation Upper Mamuniyat on a field scale. The resulting reservoir separation is complimentary to VRMS and coherency cube observations and in agreement with regional FMI and core facies interpretation.
-
-
-
The Application of Multiple Realizations of Geostatistical Inversion for Supporting Geological Objectives
By K. FilippovaThe efficiency of application of geostatistical inversion technique and especially multiple realizations analysis for supporting geological objectives of brownfield stage are presented in this paper. Two oil fields case studies (a clastic and a carbonate reservoir) are used for demonstrating it.
-
-
-
The Integration of Core and Borehole Image Information and Resulting Depositional Model - Moreni Field, Miocene-pliocene
Authors C. J. Cubitt, B. C. Stummer, P. V. Grech and L. E. A. ScheucherThe Levantine and Meotion reservoirs of the Moreni Field of Romania (discovered in 1898) were characterised for the first time using modern, wireline, core and bore hole images (BHI). Integration of this newly acquired data facilitated the direct link between sedimentological features and BHI texture. This approach, where image facies are regarded as ‘like’ litho-facies, made a thorough interpretation of Levantine and Meotian depositional environments possible away from core control. Subsequently the pragmatic analysis of BHI/core litho-facies and depositional environments in conjunction with wireline, depositional analogues and petrology/XRD revealed that the Pleistocene Levantine Formation sediments were formed by interacting coastal and flood plain processes. In contrast Meotian Formation sediments were interpreted as having been deposited more seaward forming in a tidal lagoonal-barrier setting. This study not only revealed a new geological understanding of Moreni Field reservoirs but also the effectiveness of using a pragmatic approach to BHI and core analysis along with the consistent integration of subsequent results in combination with the use of depositional analogues.
-
-
-
Bilondo Reservoir Model - New Geology and Geophysics Integrated Approach
Authors A. Mazeraud, F. Duclos and S. B. AhnThe geological modeling of a field is an important issue, from the appraisal stage (to its development) and during its whole production life cycle. However, results are highly dependent on constraints imposed by reservoir geologists, as for example the size of the main heterogeneities linked to both the size of input facies variograms and geological concepts. It is possible to enhance the heterogeneity characterization by constraining the model with seismic attributes. The result will depend on the seismic quality and some parts of the models could be affected by geophysical artifacts. A new methodology has been developed to combine multiple seismic attributes with geological information in order to obtain a more realistic model. The final result is no more dependent on the input variography/stochastic realizations and will also be less affected by possible seismic artifacts. Finally with the early use of 3D seismic information in the model, we consider to have a more realistic vision of the field that should help for the integration of all static and dynamic information. This innovative workflow has been developed through the case study of Bilondo Oil Field, a Deep Offshore Miocene turbiditic reservoirs located in deep offshore Congo Republic.
-
-
-
An Integrated and Predictive Workflow Model for the Exploration and Development of Unconventional Shale Reservoirs
Authors E. C. Andersen, H. Davey, C. Steinhoff and T. DavisIn unconventional shale reservoirs, hydraulic fracturing is necessary to create sufficient permeability for commercial production. In the past, a dominantly statistical approach was used for hydraulic fracture treatments assuming a standard well spacing, perf spacing, lateral length, fluid volume, and proppant amount could be applied to all reservoirs at all depths. However, it is becoming increasingly apparent that there is a complex interplay between natural and induced hydraulic fracturing. The stress state and corresponding density, orientation, and connectivity of in-situ fractures can provide abundant information about how the rock may respond to induced hydraulic fracturing. New integrated technologies are required to explore for and develop shale reservoirs. Since every shale reservoir is different, establishing workflows in the applications of these technologies is critical to specific purposes from the exploration to the production phases. Adjusting drilling and completions strategies to reflect geomechanical changes in the rock is critical Using a multi-component 3D/3C dataset, an integrated geomechanical research project has been devised in conjunction with the Colorado School of Mines’ Reservoir Characterization Project (RCP) comprising of both geologic and geophysical studies in rock properties.
-
-
-
Simultaneous Time-lapse Binning and Regularization of 4D Data
Authors P. J. Smith, I. Scott and T. TraylenThe time-lapse seismic method compares repeated 3D reflection seismic cubes acquired at different dates. Time-lapse binning is routinely used to ensure that these 3D cubes are created from recorded seismic traces that are as similar as possible, with poorly repeated traces being discarded. Another important component of time-lapse seismic processing flows is the conversion of the irregularly and differently sampled seismic surveys into collocated measurements that can be accurately compared. This regularization procedure is usually performed independently of time-lapse binning, and the binning may well discard traces that would have benefited the regularization and subsequent imaging. We have developed a procedure that combines time-lapse binning and regularization into a single algorithm, thereby achieving an optimum compromise between inter-survey trace repetition accuracy and image quality. Initial results on real time-lapse seismic data sets are promising.
-
-
-
A Novel Method of 4D Analysis and its Application to Land Seismic Data
Authors R. M. Burnstad, M. A. Jervis and A. V. BakulinAn alternative to traditional 4D seismic repeatability metrics is proposed. The new metric is based on surface consistent, iterative least-squares analysis of pre-stack seismic data in common source and receiver domains. It is simultaneously estimated across multiple time-lapse seismic surveys. Two sets of scalars are produced, one that is common to all surveys, and one that changes with each survey. The second set of scalars contains information on 4D repeatability. The new repeatability analysis method is applied to data acquired for a seismic monitoring experiment in a carbonate oil field in Saudi Arabia. The results indicate that buried hydrophones are less repeatable than the colocated geophones. These conclusions and the new metric are confirmed using post-stack normalised root mean square (NRMS) repeatability analysis on data recorded using high source density 2D swath line acquisition into the same permanent receivers.
-
-
-
4D Processing between Variable-depth and Conventional Streamer Data
Authors P. Charrier, Z. Yu and T. RebertProcessing data with variable-depth streamer acquisition has recently become possible through a new advanced algorithm called joint deconvolution (Soubaras, 2010). In this particular acquisition, the receiver depth increases smoothly with offset and this allows for a wide diversity of receiver ghosts to be recorded. This acquisition and associated processing increases dramatically the possible frequency bandwidth. While most acquisitions in the future will certainly be realized with broadband techniques, the question of 4D matching between conventional and BroadSeis data must now be addressed during an intermediate period when the baseline data is a conventional acquisition. The case between BroadSeis and conventional data has one problem to solve: the difference in cable profiles. This paper considers this problem, addresses the following topics: wavelet processing, time de-striping, 4D binning, regularization, imaging, final matching and demonstrates that a relevant 4D response can be obtained.
-
-
-
4D Seismic Wave-equation Depth Migration Velocity Inversion
Authors J. C. Shragge and D. E. LumleyTime-lapse analysis of 4D seismic data acquired at different stages of hydrocarbon production or fluid/gas injection has been very successful at capturing detailed reservoir changes (e.g., pressure, saturation, fluid flow). Conventional 4D seismic analysis is performed in the time-migrated image domain and assumes a fixed migration velocity model; however, this assumption is violated when the subsurface velocity is significantly altered by production/injection effects, resulting in large time-shift anomalies and complex 4D scattered wavefield coda. We argue that these situations require a more robust 4D analysis procedure that involves iterative wave-equation prestack depth migration (PSDM) and time-lapse velocity analysis. Herein, we adapt a 3D image-space wave-equation migration velocity analysis (WEMVA) approach that backprojects discrepancies (residuals) in 3D/4D migrated images to form 3D/4D velocity model updates. We discuss the differences between 3D and 4D WEMVA inversion goals, and how we localize 4D WEMVA perturbation estimates to around the reservoir zone to generate high-resolution velocity model updates. We demonstrate the benefits of 4D WEMVA analysis in a synthetic CO2 geosequestration experiment by successfully inverting for a velocity model perturbation corresponding to a thin layer (< 20m) of injected CO2 in a North Sea analogue reservoir.
-
-
-
Building a Sequence Stratigraphic Framework from HorizonCube and Well Data
Authors F. Qayyum, P. de Groot, J. Yasin and G. AkhterTo build an accurate subsurface sequence stratigraphic framework, an interpreter ideally needs to correlate all seismic events with available well data. Without a (semi-)automated correlation approach, such a workflow is not feasible. In this article, we present a workflow that integrates seismic data and well data through a HorizonCube, a dense set of auto-tracked seismic events. The mapped events are simultaneously analysed in the relative geologic time (Wheeler) domain and in the structural domain. Among others, HorizonCube derived attributes are extracted to help analyse relative changes in sedimentation rate, base level variations, depositional trends and geomorphologic patterns. All extracted information is collectively interpreted and calibrated to well data. The workflow is illustrated in two subsurface case studies representing a fluvio-deltaic and a mixed silliciclastic-carbonate settings.
-
-
-
3D Fault Detection Using Structure Prediction and Nonstationary Similarity
More LessAutomatic detection of geological discontinuities, eg., faults, is a crucial problem in the interpretation of 3D seismic data. We present a new fault detection technique based on the nonstationary similarity attribute. We use local dip pattern to form a structural prediction of seismic traces from neighboring traces. Local similarity between original data and predicted data enhances the coherency-type analysis with identification. In comparison with coherency attribute using slide-window correlation, nonstationary similarity indicates local measurement of fault. Numerical tests using field data in 2D and 3D confirm the effectiveness of the proposed technique for 3D fault detection.
-
-
-
Hybrid Dip Estimation
Authors A. A. Aqrawi and T. H. BoeDip estimation is fundamental step in seismic interpretation, and is often used to guide seismic attributes calculation such as smoothing and edge detection. However, estimating dip accurately is a fairly compute intensive task that can slow down calculations of attributes considerably. Here we compare two established and robust methods for calculating dip, and one simpler and faster but less accurate method with regards to dip field detail, consistency, robustness and compute time. As the fast but less accurate dip estimation method gives good dip estimates in most cases, but suffers from producing some outliers, we propose a dip estimation method that is a hybrid between the fast method and a more robust but slower method. By re-estimating any extreme dips with a robust method, we demonstrate that a hybrid method can produce a dip-field of similar detail and quality as the best robust method in significantly less computation time.
-
-
-
Robust 2D Hilbert Atributes of Local Amplitude and Phase
Authors A. Solberg, A. Jensen and L. J. GeliusInstantaneous amplitude and phase are based on the 1D Hilbert transform of seismic traces. We present alternative attributes with improved localization properties by applying a combination of orientation-adaptive Hilbert transforms and bandpass filtering. The concept of local amplitude and phase are first explained for the 1D case, before extensions to 2D are given. In the 2D case, the process consists conceptually of two steps: First, the dominant local orientation is estimated, and then the local amplitude and phase are estimated along that orientation. The proposed attributes are compared to the classical instantaneous attributes both for a thin-bed resolution image with a classical wedge model, and for a seismic data set. They show better localization properties for the thin-bed wedge model, and a higher robustness and lateral continuity on the real seismic data.
-
-
-
A Method to Estimate Volumetric Curvature Attributes in 3D Seismic Data
Authors L. O. Martins, P. M. Silva and M. GattassVolumetric curvature attributes can provide, for each volume sample, a measure of bends and breaks in seismic reflectors, capturing subtle variations caused by faults and folding that were not obvious in amplitude field. This paper aims to propose a new method to compute volumetric curvature attributes from 3D amplitude data. Seismic horizons can be understood as level surfaces described by some implicit function F. Such implicit function can be viewed as a local surface identifier, in sense that more probable surface samples are closer to some constant value. We propose three seismic attributes in order to describe seismic horizons as level surfaces: Adjusted instantaneous phase, vertical derivative and ridge/valley detector. For each attribute, partial derivatives provide a normal field for seismic horizons in 3D space. Using this normal field and differential geometry, we can obtain curvature measures such Gaussian curvature, mean curvature, and principal normal curvatures.
-
-
-
Seismic DNA - A Novel Seismic Feature Extraction Method Using Non-local and Multi-attribute Sets
Authors J. Ø. H. Bakke, O. Gramstad and L. SønnelandWe present a new approach to extract features from seismic data using a non-local and multi-attribute search method. By transforming seismic reflection data and attributes derived from seismic data into characters we can search for complex features in the seismic data volumes using a text-based search technology. The method presented here allows for feature patterns with a varying vertical extent, varying attribute values and a varying number of subfeatures in the feature signature. We describe the method and give two examples of how it can be used. The first one shows how the number of subfeatures can vary in a feature. The second one shows how we can combine different attributes in one search.
-
-
-
Self-constrained Inversion of Potential Fields
Authors M. Fedi, G. Florio, S. Ialongo, V. Paoletti and F. CellaWe propose a constrained inversion procedure based on a priori information derived exclusively from the potential field data themselves (self-constrained inversion). To set up effective constraints, we utilize two source parameters, namely the structural index N and the position of the source body edges, both estimated through analysis of the field itself. With some synthetic examples, we show that this information, incorporated in the objective function as depth and horizontal weighting functions, is enough to obtain rather accurate and realistic magnetization models.
-
-
-
A New Stabilizer for ERT Inversion
Authors G. P. Ke, H. Dong and Å. KristensenSmoothness inversion under L2 norm regularization does normally not provide enough resolution for certain inversion problems, especially for models with interface reconstruction and edge preserving. In this paper we propose a new stabilizer based on the same mechanism as the minimum gradient support (MGS) stabilizer. Combined with nonlinear conjugate gradient method, the new stabilizer gives excellent results for electric resistivity tomographyic (ERT) inversion problem. The comparison of the new stabilizer and MGS stabilizer is also discussed.
-
-
-
Reserves Estimation from 3D CSEM Inversion for Prospect Risk Analysis
More LessNet rock volume is the main uncertainty affecting the evaluation of recoverable reserves for prospect risk analysis. We present a Monte Carlo method for estimating a net rock volume probability distribution from an anisotropic 3D CSEM inversion result. Given a CSEM favourable exploration setting, the method can significantly reduce the uncertainty in net rock volume, especially for stratigraphic traps. The method relies on the sensitivity of CSEM to the volume of resistive rock and on the transverse resistance equivalence principle for relating the low resolution inversion result to possible reservoir scenarios at the well log scale. We demonstrate the performance of the method using unconstrained inversion results from a full-azimuth 3D CSEM survey over a known oil field. No prior information in terms of well data or field geometry was assumed to simulate an exploration case. The uncertainty associated with the resulting net rock volume probability distribution as measured by the P10/P90 ratio is less than 6, which is considered low by common industry practice. The actual net rock volume defined by the reservoir top and the oil-water contact coincides with the 60th percentile of the distribution, i.e. the predicted range of possible net rock volumes is very reasonable.
-
-
-
Heavy Oil - Timelapse Fluid Influences and Mapping
Authors H. Morris, C. Dumitrescu, M. Kitteridge and M. SmithUnderstanding the sensitivities of temperature, pressure and saturation changes to the rock properties is key to allowing us to identify changes in the 3D/4D environment. Here we review the magitude of the different influences and show how we can map the summation of these influences in the subsurface. Once we have done this we can highlight remaining areas of un-affected reservoir. This paper is the first of two which highlights the changes within a Steam Assited Gravity Driven (SAGD) environment.
-
-
-
Integrated Monitoring of the CO2 Storage Ketzin Using a Structure-based Combination of Seismics and Geoelectrics
Authors P. Bergmann, M. Ivandic, D. Kiessling, C. Rücker, C. Schmidt-Hattenberger, S. Lüth, C. Juhlin and B. NordenGeophysical monitoring at the CO2 pilot storage Ketzin comprises time-lapse seismic and geoelectric (ERT) measurements. Both types of measurements are known to image geological structures differently, in particular for a variable saturation of CO2. We present a combination of both methods by means of a structural constrained inversion approach. Structural constraints are implemented in the geoelectric inversion by a local regularization. This allows model parameters to behave discontinuously across prominent geological boundaries. A tetrahedral finite-element parametrization is used to closely follow geometric a priori structures interpreted from seismic reflection data. Thus, seismics and geoelectrics are arranged in a sequential workflow which is based on a structural similarity. Practical application is performed on the Ketzin datasets which comprise repeated 3D seismic surveys, as well as repeated surface-downhole geoelectric surveys, providing different illumination/coverage and time-lapse signals. However, application of a local regularization for the caprock-reservoir boundary yields a more consistent image and reduces some of the ill-posedness in the ERT inversion. We compare the result with that of an unconstrained inversion and discuss its potential for CO2 migration imaging.
-
-
-
Repeat Time Lapse 4D Seismic Monitoring as a Tool for South Arne Field Development
Authors O. V. Vejbaek, A. King, J. E. Palmer and K. HansenWe present a time-lapse 4D seismic case history from the Hess operated Danish South Arne field. Results from 4D monitor surveys are time critical if they are to have maximum impact on field management issues. Definition of precise survey objectives by the integrated reservoir management team enables the design and rapid execution of a 4D seismic monitor program. Such data sets can deliver timely information critical to impact current work-over programs and new drilling opportunities, plus give additional information for reservoir characterization. Key to the project turnaround is the use of calibrated and automated acquisition technologies, which provide an accurate repeat of source and receiver positions, and enable the use of deterministic seismic data processing flows. We demonstrate how such a towed streamer monitor survey was acquired with delivery of time lapse data volumes within 2.5 weeks of last shot, and describe the impact this data has had upon the ongoing reservoir management and characterization of the South Arne field.
-
-
-
Technical and Geological Review of Carbon-dioxide Geosequestration along with Analysis of Various Monitoring Techniques
More LessGeological sequestration is a potential means to reduce large amount of CO2 that is released into the atmosphere from petroleum developments as well as other stationary sources. Technical steps for CO2 geological sequestration include separation, dehydration, compression, transport, injection and monitoring. Reservoir and geological studies are important, especially to optimize the sequestration process and to determine the extent to which the CO2 moves within the geologic formation. This information is key to ensure that sequestration will not impair the geologic integrity of an underground formation and that CO2 storage is secure and environmentally acceptable. This paper has discussed about the technology involved in CO2 geological sequestration process, its reservoir & geological perspectives, the storage problems, various monitoring methods and techniques for safe injection of CO2. Analysis of various monitoring techniques currently in use was done and is presented for review and evaluation from great number of sources. Hence consideration of all the reservoir and geological aspects along with effective monitoring of Sequestration process would lead to the safe storage of CO2 underground which could be used later for various purposes thereby also standing as a key tool in tackling climate change, providing energy security, creating jobs and economic prosperity.
-
-
-
Geology and the Effects on Filling Pattern in CO2 Storage Sites
By P. FrykmanThe filling of a reservoir with CO is a dynamic process influenced by heterogeneities at a range of different scales. If parts of the reservoir are by-passed during this process it will result in lowered filling efficiency and therefore smaller capacity than if assuming homogeneity. This study attempts to illustrate that even small-scale heterogeneity has implications for how the CO is distributed and trapped in sedimentary sequences, and outlines a workflow for the study of these effects. In certain reservoirs the distribution of the injected CO into partly or fully separated layers might mean efficient use of the pore space in the reservoir. However, the mobility may also cause CO to bypass some of the pore space, depending on the heterogeneity and anisotropy of the permeability. After injection has stopped, the heterogeneity will influence the imbibition process when brine displaces the CO, which might cause additional trapping beyond that prescribed by the endpoints for the saturation functions.
-
-
-
Time-lapse Analysis of Sparse 3D Seismic Data from the CO2 Storage Pilot Site at Ketzin, Germany
Authors M. Ivandic, C. Yang, S. Lüth, C. Cosma and C. JuhlinIn April 2004, a research pilot project in the German town of Ketzin started as the first onshore CO2 storage project in Europe. Injection started in June 2008 and until the latest repeat survey in February 2011 around 45 kilotons of CO2 had been injected into a saline aquifer at approximately 630 m depth. Different seismic methods, such as time-lapse Vertical Seismic Profiling, Crosswell, Moving Source Profiling and surface seismics have been employed to detect and monitor changes in the reservoir. We present here time-lapse results from sparse pseudo-3D seismic surveying with a radial distribution of acquisition profiles directed towards the approximate location of the injection well, which were acquired to link downhole surveys with full 3D surface seismic surveys. The results are consistent with the 3D seismic time-lapse studies over the injection site and show that the sparse 3D geometry can be used to qualitatively map the CO2 in the reservoir at a significantly lower effort than the full 3D surveying. The last repeat survey indicates preferential migration of the CO2 to the west. There are no indications of migration into the caprock on either of the repeat surveys. The same observation was obtained from the full 3D dataset.
-
-
-
The Effect of Coal Rank on the Wettability Behavior of Wet Coal System with Injection of Carbon Dioxide and Flue Gas
Authors N. Shojai Kaveh, E. S. J. Rudolph, K. H. A. A. Wolf and S. N. AshrafizadehThe injection of carbon dioxide (CO2) or flue gas into coal layers enhances the coal bed methane production (ECBM) and is also an option for CO2-storage. The success of this combined process depends strongly on the wetting behavior of the coal, which is a function of coal rank, ash content, pressure, temperature and composition of the gas. Two coal samples have been used for this study representing different ranks: hvBb and semi-anthracite rank. The wettability behaviour of the wet coal samples upon injection of synthetic flue gas and pure CO2 was investigated in a modified pendant drop cell at a constant temperature of 318 K and pressures varying between 0.1- 16 MPa. For the hvBb sample, the wettability of the coal surface changed from intermediate-wet to CO2-wet at pressures above 8.5 MPa . When injecting synthetic flue gas, only a change from water-wet to intermediate-wet was observed. For the semi-anthracite rank Selar Cornish sample and CO2 injection this alteration was observed at about 5.3 MPa. Experimental results with synthetic flue gas revealed that the wettability of Selar Cornish coal is intermediate wet at all pressures and the contact angle only slightly increases with increasing pressure.
-
-
-
CO2 Brine-rock Interactions in Reservoir Chalk Rock – An Experimental Evaluation at Reservoir Conditions
Authors J. F. Zuta and C. KjøllerCO2 flooding can improve oil recovery in chalk plugs with low matrix permeability. However, several coupled physical and chemical processes may occur. These phenomena can either increase and/or decrease the injectivity. A series of dynamic laboratory experiments have been used to investigate CO2-brine-rock interactions during CO2 injection in a reservoir chalk rock. The experiments were designed to represent the various situations in the field – near well-bore or far field regions. The experiments consisted in the injection of CO2-WAG at reservoir conditions and CO2 saturated water at supercritical CO2 conditions. The experiments were carried out in plugs with either Swi= 100% and/or Swi= 15%. A novel sampling technique was used to sample produced fluids under pressure without disrupting the injection process. Results based on chemical analyses of produced fluids lead to a comprehensive understanding of the coupled mechanisms taking place. Based on the measured Ca-concentration and alkalinity, the presence of oil was observed to slightly delay the calcite dissolution process. Wormholes evident of calcite dissolution were seen on the inlet sides of the plugs after the flooding process. Pre and post-floods petrophysical analyses of the plugs also showed some porosity and permeability increase as a result of flooding.
-
-
-
CO2 Storage Atlas of the Norwegian Part of the North Sea
Authors E. Halland, F. Riis, W. T. Johansen, I. T. Gjeldvik and C. MagnusIn our work we have evaluated the storage possibilities in large saline aquifers, defined structures, abandoned fields, and the use of CO2 in producing fields to enhance recovery. With a success rate for hydrocarbons at around 50% on the NCS, around 50% of exploration wells have been proven dry. An assessment of why, has provided us with an interesting number of structures, in terms of CO2 storage. Though aquiferes that seems to be most suitable for CO2storage is not always where the highest petroleum activities are, we could draw on a lot of geological knowledge and a lot of reservoir data from similar formations in order to calculate the storage capacity.
-
-
-
Numerical Simulations for Acoustic Reflection Imaging with FDM and FEM
More LessAcoustic reflection imaging can be applied to detect fractures or interfaces away from the borehole. Although acoustic reflection imaging tools have been available for nearly a decade, some problems still remain. The most difficult are those involved in extracting reflection waves from dominant borehole mode waves, and imaging a complex geologic body exactly. Numerical forward modeling can help us to understand the wave field for acoustic reflection logging, and to verifying the data processing algorithms. In this paper, we report developments in the finite difference method (FDM) and finite element method (FEM) programs to acoustic reflection imaging cases. In particular, the FEM program is employed first to simulate a formation interface and then a fluid-filled fracture outside the fluid-filled borehole model. The FDM is applied in conjunction with an equivalent medium method to simulate the response of fractures outside a borehole. Our results demonstrate that the equivalent medium method can be utilized with the FDM to simulate a fractured formation model effectively. Although the FEM can simulate the reflection logging more accurately, the associated increased computational costs must be justified. For simple models such as linear fractures and interfaces, the FDM may produce a sufficiently accurate result.
-
-
-
An Effective Data Processing Flow for the Acoustic Reflection Image Logging
More LessRecent studies have revealed the great potential of acoustic reflection logging in detecting near borehole fractures and vugs. In this paper, we present an effective data processing flow for acoustic reflection image logging by employing a multi-scale slowness-time-coherence method for reflection wave extraction and a Kirchhoff migration for near borehole structure imaging. And the corresponding software has been developed. We first apply the software to process the synthetic data of acoustic reflection logging in a borehole surrounded by interface and fractured formation models generated by a 2D finite difference method (FDM), in conjunction with the equivalent medium model to test the validity of our method and the processing flow. We then apply it to the physical modeling data from a large water tank in laboratory and the field data from two wells in a western oil field of China. As a result, applications of the processing flow to synthetic data, physical modeling data from a laboratory water tank as well as the field data demonstrate the validity and capability of our MSTC, Kirchhoff algorithms and the new-developed software.
-
-
-
The Potential of Single-well Acoustic Imaging for Detecting the Direction and Distance to a Target Borehole
Authors M. A. Jervis, A. V. Bakulin, T. L. Tonellot, I. A. Ghamdi, A. Shabbir and H. YamamotoA new method to locate nearby boreholes using acoustic imaging is presented. The challenge of locating a nearby well from a borehole is commonly addressed with electromagnetic (EM) or passive magnetic ranging methods, which can suffer from poor resolution and penetration and require the presence of a conductive or magnetic casing. Single-well acoustic imaging has great potential for locating a nearby borehole at higher resolution and with fewer of the limitations of EM-based methods. Acoustic imaging requires only an impedance contrast between the target object and the formation, which is adequately provided by the presence of a fluid-filled borehole. Two tests are shown demonstrating the capabilities of the new method. In the first test, a vertical borehole is located and imaged from a nearby horizontal well, and in the second test, a vertical borehole is imaged from a nearby near-vertical well. In both cases the estimated distances were validated by independent measurements.
-
-
-
Analysis of Sensitivity of Array Resistivity Log to Fresh Mud Invasion and Inversion for Oil-water Recognition
Authors S. G. Deng, Q. T. Sun, H. Li and N. N. HuoIn order to improve reservoir fluid recognition, the sensitivity of array resistivity response to the difference of the invasion property in both oil-bearing layer and water layer is analyzed. Then the primary inversion is carried out based on the array resistivity log. Differing from the monotonic resistive invasion profile of water layer, the radial resistivity of fresh mud-invaded oil-bearing layer presents complex distribution characteristics, such as nonlinear increase, increasing to decreasing and low resistivity annulus. Under certain conditions, array resistivity log can reflect these changes and the array induction log is more sensitive. Nevertheless, due to the effect of factors like large invasion depth, reservoir physical property and oiliness, the resistivity can exhibit great deviation from the actual mud filtrate invasion profile. We construct a five-parameter formation model to simulate the complex resistivity distribution of fresh mud-invaded formation. Then, based on the principle of non-linear least squares, the measured array resistivity log is used for inversion with the Marquardt method. It is demonstrated that the inverted resistivity presents a typical nonmonotonic variation in oil-bearing layer and a monotonic variation in water layer, which agrees well with the actual invasion property. This can help to realize efficient reservoir fluid recognition.
-
-
-
Fracture Characterization in Tight Carbonate Reservoirs of Kuwait through Advanced Borehole Imaging Approach
Authors B. Khan, S. K. Singh, R. Abu-Taleb, A. Abu Ghneej, S. Bader, D. B. Roy and A. AviantaraFractured carbonate reservoirs within Marrat, Sargelu and Najmah formations are major hydrocarbon producers in Kuwait. Hence, fracture characterization of these reservoirs is vital. OBM, traditionally used to drill these reservoirs, inhibits acquisition of high resolution resistivity image hampering identification of complex features and determination of fracture properties. To overcome these limitations, formate mud was used in selected wells facilitating acquisition of high resolution image data. This paper presents advanced borehole imaging approach to fracture characterization utilizing high resolution image in formate mud and its advantages over conventional image in OBM. In the studied wells, fractures were classified into continuous open, discontinuous open, partially cemented and cemented. The open fractures have dominantly NE-SW strike, whereas, the cemented fractures show a dominant NW-SE strike. The fracture porosity is in the range of 0.1-0.2%. The advanced approach has shown marked improvement in terms of defining the geometry, appearance and continuity of the fractures. Good estimation of fracture aperture and porosity has also been achieved, which was hitherto not possible with borehole image in OBM. The information have been very useful in finalizing test intervals in drilled wells and are fundamental input to DFN models for predicting fracture clusters and identifying future well locations.
-
-
-
Improve Reservoir Rock Permeability Using Laser Technology - A New Advanced Approach for Increased Oil Production Rate
More LessLasers have potential for rock destruction applications in mining, petroleum, tunneling, and trenching. The high temperatures induced using high power lasers cause an increase in porosity and permeability, while reducing rock strength making it easier to break-up rocks. These results are part of a more extensive research project studying the application of laser technology in the oil and gas industry. Pre- and post-lasing analysis included mineralogy determination, clay characterization and original fractures, as well as porosity, permeability. The characteristics of unlased rocks were compared to the characteristics of lased rocks in order to determine the effect the high temperature caused by lasers has on altering the rocks. Over 18 core samples where exposed to laser energy in laboratory settings. Rocks types lased include sandstone, limestone, and shale. Permeability and porosity of the reservoir rocks ranged from 0.02 to 628 md and 100% to 400%, respectively. It was found that high temperature caused by lasers enhance porosity and permeability because high temperature vaporizes or breaks cementation leading to more pore space.
-
-
-
Experimental Evaluation of Rock Spallation with Laser Irradiation
Authors G. H. Montazeri, M. Bakhtbidar, A. Safaei and A. FakhriWhen lasers were invented in 1960, they were called “a solution looking for a problem.” Since then, they have become ubiquitous, finding utility in thousands of highly varied applications in every section of modern society, including consumer electronics, information technology, medicine, industry, entertainment and the military. Research conducted in rock destruction by high-power lasers indicates that lasers can be a less expensive, environmental friendly alternative to conventional drilling and perforating methods. Laser rock spallation is a rock removal process that utilizes laser-induced thermal stress to fracture the rock into small fragments before melting of the rock occurs. High intensity laser energy, applied on a rock that normally has very low thermal conductivity, concentrates locally on the rock surface area and causes the local temperature to increase instantaneously. The maximum temperature just below the melting temperature can be obtained by carefully controlling the laser parameters. This results in a local thermal stress in subsurface that is enough to spall the rock. This process continues on a new rock surface with the aid of the high pressure gas purging blowing away the cracked fragments. Laser parameters that affect the laser spallation efficiency will be discussed in the paper.
-
-
-
Difficulties in Simulating Diffusive Flux in Matrix-fracture Model
Authors M. Khosravi, B. Rostami and S. A. MirazimiDiffusion is an influential mechanism in oil recovery, which accelerates miscibility achievement, and usually has difficulties in modeling by commercial software. Previous studies have illustrated that compositional software could not calculate diffusion flux properly between two neighboring grids, in which oil saturation has a sudden drop from 1 to 0. Therefore, a dummy zone with medium oil saturation has to be defined at the oil/gas interface; however, this would affect the material balance and fluid flow. Furthermore, it is impossible to use such a method in a dual-pore fracture model and it would impose severe restrictions for full field simulation. In the first part of this work, a comprehensive review has been done on estimation of diffusion coefficients. Also, simulation of miscible CO2 displacement in fractured models has been reviewed and simulation difficulties have been widely discussed. Then, to analyze diffusion flux specifically, a 1-D horizontal model with neither viscose nor gravity force is simulated using two of the most famous compositional simulators, and their results are compared with analytical solution of the problem. Next, experimental results of miscible CO2 injection in a fractured system have been used to examine the new approach on simulation of a more complicated case.
-
-
-
Field Development Optimization under Uncertainty Using an Ensemble-based Simulation Approach
Authors R. Schulze-Riegert, O. Pajonk and M. NwakileField development optimization under geological uncertainties defines a major challenge for reservoir management. Historical production data is used to calibrate reservoir simulation models and thereby reduce the variability of geological uncertainty distributions. The practice of using a single history matched model to evaluate forecast scenarios is questionable, as they prove to be a poor basis for including uncertainty descriptions. In recent years ensemble-based approaches have been increasingly applied in history matching workflows to account for consistent uncertainty descriptions. Any uncertainty description becomes relevant for field development planning, however, it is less obvious how to integrate the ensemble into a field development optimization process. In this paper we use an Ensemble Kalman Filter technique (EnKF) to generate a history matched ensemble. A workflow is developed to identify representative ensemble members based on key performance indicators. All selected cases are included in an integrated field development optimization process. A risk-averaged objective function definition is used to evaluate field development scenarios for multiple ensemble members. Full uncertainty distributions for optimized field development scenarios are derived on the bases of the full history matched ensemble. The workflow is applied to a real field case and results are discussed.
-
-
-
Difficulties and Strategies of Integrated Reservoir Studies
Authors Y. S. Yan, T. Ma, T. C. Wang and Z. K. XuIntegrated reservoir study is a very complicated systematic engineering which covers many different disciplines. In most of oilfields in China, complicated geological settings, conventional enterprise organization structures, current reservoir management models, various third party applications and massive E&P data have made integrated reservoir studies face great challenges. For these problems, firstly, we proposed a concept model for integrated reservoir studies. This model provided a fundamental architecture for information sharing and fusion of multi-disciplines. Then, we developed an information sharing method based on the principle of autocorrelations. Finally, we proposed an IT solution for integrated reservoir studies.
-
-
-
Cross Disciplinary GRM on Visund Nord - Model Update as Basis for New Wells
More LessThe satellite wells in the northernmost part of the Visund field were shut down in 2006 due to gas leakage, with the result of hydrates damaging the oil pipeline to the platform. Geophysical Reservoir Monitoring (GRM) has been important in the model building and updating. The decision of subsea re-development of the Visund Nord area has been made, and drilling will start in Q3 2012. By thorough cross disciplinary use of production data and geological and geophysical interpretation of 4D seismic, the Visund Nord dynamic reservoir model has been updated. The new model makes the basis for placement of two new oil producers east in the area and an additional exploration pilot. It is likely that another two wells will be drilled from the sub sea template in the future.
-
-
-
Seperating Temperature & Saturation of Fluid Influences in a Timelapse Heavy Oil Environment
Authors H. Morris, C. Dumitrescu and B. HardyThe heating of oil sands via steam in a SAGD environment has a significant impact on the rock properties. The rock physics in this study identifies temperature influences as the major cause of elastic property change within the reservoir, and therefore mapping of this heat transfer within the reservoir is very feasible and it is clearly evident in the time-lapse seismic (as presented in part A). Additionally and possibly more importantly though we are able to use the rock physics to break apart the temperature and saturation effect to unmask the movement of the fluid types so we can determine the true time-lapse oil saturation, and identify where is being swept efficiently, and where is just being heated.
-
-
-
A Multidisciplinary Application for an Exploration Well in the Tano Basin, Ghana
Authors C. Carugo, S. Joshi, L. Magini and G. N. PinnaIn a difficult exploratory environment, consisting of tight formations and high pressure zones, the combination of advanced gas detection and advanced fluid analyser application, enable a complete petrophysical investigation and understanding of rock quality and potential of the reservoirs. The multidisciplinary approach involved specialists based at the rig site and in different locations, interacting via the operator.
-
-
-
Novel Thermodynamic Scale Equation for Modelling of Asphaltene Precipitation under Gas Injection
More LessAsphaltene precipitation and deposition is one of the problems that have been reported during the primary reservoir depletion and/or enhance oil recovery such as miscible or immiscible gas injection. Extensive experiments for measuring asphaltene deposition has been conducted with different gas ratio with associated gas in one the oil fields in south of Iran. Different thermodynamic model was assisted for evaluating of experimental data which had not enough quality in prediction. Asphaltene thermodynamic model due to very complicated nature and behaviour of asphaltene and its aggregation and precipitation could not accurately predict asphaltene precipitation due to gas injection. Most of the time they need a lot of tuning or matching parameters that could fit the asphaltene precipitation in isothermal or under pressure depletion very well. But their prediction is not strong enough to relay to them for planning the enhance oil recover scenario especially immiscible gas injection. New scale equation therefore, has been developed to predict asphaltene deposition with more reliability respect to literature thermodynamics models. Results of modelling of asphaltene precipitation under gas injection indicates very good agreements with experimental data and shows the scale equation could be better tools respect to the other thermodynamic models.
-
-
-
The Effects of Ultra-high Pressure and Temperature on the Rheological Properties of Water-based Drilling Fluids
Authors M. Amani, A. Shadravan, M. Al-Jubouri, M. Al-Waily and Y. El WardanyThe future of oil and gas exploration and production lies greatly in reaching to hydrocarbon resources that are located in deeper formations. As we drill into deeper formations we will experience higher pressures and temperatures. Understanding the rheological characteristics of the drilling fluids under elevated pressures and temperatures is essential for the drilling engineers. There is relatively little systematic understanding of how the flow behavior changes with downhole conditions. The rheology of the fluid is influenced by many factors. This research is focused on developing a methodology for testing and investigating the rheological behavior of water-based drilling fluids with different properties at HPHT conditions using a state-of-the-art viscometer capable of accurately measuring drilling fluids properties up to 600F and 40,000 psig. There is almost no published data to for changes in Drilling Fluids behavior under such Ultra-high pressures and temperatures. The results of this study show how the Viscosity, Yield Point and Gel Strength of a Water-based Drilling Fluid change under such conditions.
-
-
-
Use of Field-wide Seafloor Time-lapse Gravity in History Matching the Mikkel Gas Condensate Field
Authors J. N. Vevatne, H. Alnes, O. Eiken, T. Stenvold and F. VassendenTo monitor water influx, seafloor gravity and subsidence measurements have been acquired at 21 seafloor stations above the Mikkel gas field in the years 2006 and 2011. Time-lapse repeatability is on average 2.2 uGal in gravity and 3.1 mm in depth (standard deviation). This paper compares the gravity data with forward gravity estimates from the Mikkel pre-survey simulation model. It shows how an updated model containing significantly less water gives an excellent gravity match. Knowledge of water influx is important for long-term planning and can affect the ultimate recovery of the field. This updated simulation model also shows a significantly better subsidence match than the older model. Using the subsidence data, the pore compressibility has been estimated. The results show that gravity monitoring is feasible not only on huge fields, but on a modest size gas field at medium depth.
-
-
-
Coarsening Criteria for Reservoir Upscaling
By C. Preuxhe hydrocarbon reservoirs are characterized by the distribution of their petrophysical properties which are obtained from well data and seismic information. The study of an oil field begins generally with the construction of a geological model with a fine grid. This model respects the architecture and the heterogeneity distribution of the reservoir. To correctly consider all the scales of heterogeneities, the geologists build a model with very small cells compared to the reservoir simulation size. At this detailed scale of the model, the numerical fluid flow simulations may require a prohibitively large computation time and are generally impossible to achieve. To reduce the simulation cost, reservoir engineers generally upscale the geological model to an upscaled mesh. This upscaled mesh has lesser number of gridblocks. The choice of the number of gridblocks is generally the first and critical problem to be solved. In this paper, the authors list different numerical criteria, easy to compute, which can help in evaluating the characteristics of information loss in reservoir upscaling to define the best upscaled model, in terms of precision against number of cells.
-
-
-
A Novel Approach for Combining Multiple-point Statistics and Production Data in Reservoir Characterization
Authors Y. Melnikova, K. Lange, J. Frydendall and K. MosegaardVery often history-matched models happen to be inconsistent with the prescribed complex geological model. Therefore, in recent years the need for use of multiple-point statistics as prior information in reservoir characterization problems became evident. In traditional approach one often looks only for a maximum likelihood solution in the space of models allowed by prior. However, in this case, the prior probability of the model is not quantified and, hence the consistency with prior is not guaranteed. In this study we apply a multiple-point statistics framework recently developed in our research group for the solution of history matching problem. The nature of the approach allows us to unite training-image based statistical information and production data in one objective function and guide the solution towards the maximum a posteriori model. As an example, we consider a 3D synthetic reservoir with channel-like sedimentary structures. Applying the suggested framework, we show the obtained solution to be consistent with desirable accuracy both with prior information and data observations.
-
-
-
Water in Clay and Shale - Molecular Scale and Rock Physics Modelling vs. Experiments
Authors M. I. Kolsto and R. M. HoltP- and S-wave velocities in clays and clay rich shales are strongly sensitive to the pore water, including bound water. In this work, bound water inside clay minerals and in pores within clay rich materials has been studied through discrete element modelling. An ordered structure of water near mineral surfaces is observed. The normal and shear stiffness of the bound water depend a.o. on the surface charge density, and on the salinity of the pore fluid. A simple rock physics model that contains bound water properties as input parameters has been used to compare with experimental data, largely on pure systems of compacted kaolinite and compacted smectite. The bound water appears to have a profound impact on the effective stress controlling velocities in such geomaterials.
-
-
-
-
Full-waveform Inversion in the Data and Image Spaces
Authors W. Weibull and B. ArntsenFull-waveform inversion of seismic data requires the knowledge of an initial model sufficiently close to the true model to prevent cycle-skipping. A common approach to solve this problem is to rely on velocity models estimated using ray tomography in combination with depth migration. This usually yields a smooth velocity model with kinematic properties similar enough to the true model to prevent the cycle-skipping problem. We propose an alternative approach based on wave theory only. By performing model fitting in the image space based on differential semblance a low resolution velocity model with good kinematic properties can be obtained. Cycle-skipping can be avoided by using this model as a starting model for full-waveform inversion in the data space. We show synthetic examples where an object function based on differential semblance is used to estimate an initial model and a least-squares object function is then minimized to refine the initial model.
-
-
-
Determination of Minimum Calculation Ranges for Finite Sized Gravity Models
Authors C. Mueller, P. L. Smilde and M. H. KriegerLimited calculation ranges induce errors in gravity modelling that may become quite large by disadvantageous (but still likely) density distributions. Generally valid statements regarding the required calculation range always have to be based on the density distribution with the strongest differential effect possible. With the methodology presented, the necessary calculation range can be determined for a specific density distribution of a project. This is done by determining the differential gravity effect of the external volume on any pair of points within the area of interest. If long wavelength components of these differences can be assimilated by a regional trend, they do not have to be eliminated by an increased calculation range. To shorten calculation times, with a similar approach a limiting distance and depth can be determined, for calculating gravity by line or point masses instead of prisms. With these controlled simplifications, even large model areas can be computed with the required accuracy within acceptable times; especially for joint forward and inverse modelling of Gz and gravity gradient data in the context of complex geological models and/or finely discretised density distributions.
-
-
-
Comparing Two Methods for Gridding and Honouring Gravity Gradient Tensor Data
Authors D. J. Fitzgerald, R. Paterson and H. HolsteinTo interpret Airborne Gravity Gradiometry data (AGG), a grid of the observed curvature gradients must be prepared. Methods to interpolate the full tensor and horizontal tensor (FALCON), while simultaneously honouring all the measured components, are now available commercially. Typically, this one step increases the resolution of the measured field components by 50%. We compare two field refinement techniques to further denoise the full tensor component grid estimates. The first method (MITRE), uses 3rd order tensor relations locally, in a manner analogous to Minimum Curvature, but with the correct physics for tensors. The second method uses a locally fitted truncated 3D Fourier series (T3DFS) to derive least squares fitted coefficients for the potential. The results are similar and a further denoising of 40% can be achieved. The aim is to reduce any artifacts from sample aliasing while gridding. Terrain is the single biggest contributor to any measured signal (up to 80%). This is often less than 100m away from the sensor. A detailed high resolution digital terrain model, together with an estimate of the terrain density constitutes a major influence to be removed, to then reveal the buried anomalies is critical. The influence on gridding in this process is reflected upon.
-
-
-
Invariance Rules in the Regularized Inversion of Gravity and Magnetic Fields and their Derivatives
Authors S. Ialongo, M. Fedi and G. FlorioIn potential field inversion problems we usually solve underdetermined systems and this leads to a very shallow solution, typically known as minimum length solution. This may be avoided introducing a depth weighting function in the objective function (Li and Oldenburg, 1996). In this paper we derive invariance rules for either the minimum norm minimization and for the regularized inversion with depth weighting and positivity constraints. For a given source class, corresponding to a specific structural index N, the invariance rule assures that the same solution is obtained inverting the magnetic (or gravity) field or any of its nth order vertical derivatives. Although we demonstrate mathematically this invariance rule for the minimum norm minimization only, it is shown to occur also for the regularized inversion with depth weighting and positivity constraints. In this case, a source-class invariant form of depth weighting is derived, referring to that of the magnetic field, in the magnetic case, and to the 1st derivative of the gravity field, in the gravity case. We also illustrate how the combined effect of regularization parameter and depth weighting influences the estimated source model depth in the regularized inversion with depth weighting and positivity constraints.
-
-
-
Euler Deconvolution in Cylindrical and Spherical Coordinate Systems
More LessEuler deconvolution is a commonly used technique for the semi-automatic interpretation of potential field data. In the two dimensional case the known quantities are the field strength f, its horizontal and vertical gradients, and the structural index N. The unknown quantities are deltax and deltaz, the distance from a given point to the source location in the horizontal and vertical planes. Because the equation contains two unknown quantities is is usually solved in an overdetermined least-squares inverse manner using a window of data points. Although the use of large windows can reduce the effects of noise, it can also lead to the horizontal smearing of source locations, and if a window encompasses parts of more than one anomaly then interference problems can arise. This paper discusses the conversion of Eulers' equation from a Cartesian coordinate system to a cylindrical polar coordinate system, and then demonstrates that it can be solved at each point in space without the need for inversion. The method is then extended to the three dimensional case using a spherical coordinate system.
-
-
-
Resistivity Modelling with Topography
Authors S. Penz, H. Chauris, D. Donno and C. MehlA major difficulty of electrical resistivity forward modelling is caused by the singularity of the potential occurring at the source location. To avoid large numerical errors, the total potential is split into a primary part containing the singularity and a secondary part. The primary potential is defined analytically for flat topography, but is classically computed numerically in the presence of topography: in that case, an accurate solution requires expensive computations. We propose to select for the primary potential the analytic solution defined for homogeneous models and flat topography, and to modify accordingly the free surface boundary condition for the secondary potential, such that the total potential still satisfies the Poisson equation. The modified singularity removal technique thus remains fully efficient even in the presence of topography, without any additional numerical computation. The modified secondary potential in a homogeneous model is not null in the case of topography as it would be in the classical approach. We implement the approach with the Generalized Finite Difference method. We present a 2.5D inversion example on a simple synthetic data set.
-
-
-
Modelling Anisotropy Pattern of Dry Rocks as a Function of Applied Stress
Authors M. Madadi, M. Pervukhina and B. GurevichWe propose an analytical model for seismic anisotropy caused by application of an anisotropic stress to an isotropic dry rock. We first consider an isotropic linearly elastic medium (porous or non-porous) permeated by a distribution of discontinuities with random (isotropic) orientation (such as randomly oriented compliant grain contacts or cracks). Geometry of individual discontinuities is not specified. Instead, their behaviour is defined by a ratio of the normal to tangential excess compliances. When this isotropic rock is subjected to a small compressive stress (isotropic or anisotropic), the specific surface area of cracks aligned parallel to a particular plane is reduced in proportion to the normal stress traction acting on that plane. This effect is modelled using the Sayers-Kachanov non-interactive approximation. The integral over the orientation distribution is evaluated using Taylor expansion of the stress dependency of the specific surface area of cracks. Comparison of the model predictions with the results of laboratory measurements shows a reasonable agreement for moderate magnitudes of uniaxial stress (up to 30 MPa). The results suggest that the relations between anisotropy parameters do not change with increasing stress.
-
-
-
Effects of Permeability Barriers and Pore Fluids on S-wave Attenuation
Authors B. Quintal, M. Frehner, S. M. Schmalholz, H. Steeb and E. H. SaengerWe numerically perform stress relaxation experiments using Biot’s equations for consolidation of poroelastic media to study seismic attenuation of S-waves caused by wave-induced fluid flow. Our model consists of periodically distributed mesoscopic-scale circular heterogeneities with lower porosity and permeability than the background, which contains 80% of the total pore space of the medium. This model represents a hydrocarbon reservoir, where the background is fully saturated with oil or gas (or water, for comparison), and the low porosity heterogeneities are always saturated with water. Varying the dry bulk and shear moduli in the medium, a tendency is observed in the relative behavior of the S-wave attenuation among the different saturation scenarios. First, in the gas-saturated media the S-wave attenuation is very low and much lower than in the oil-saturated or in the fully water-saturated media. Second, at low frequencies the S-wave attenuation is significantly higher in the oil-saturated media than in the fully water-saturated media. Additionally, we observed that impermeable barriers in the background can cause a significant increase in S-wave attenuation. Based on the theory of wave-induced fluid flow, our results suggest that S-wave attenuation could be used as an indicator of fluid content and permeability changes in a reservoir.
-
-
-
Integrated Numerical and Laboratory Rock Physics Applied to Seismic Characterization of Reservoir Rocks
Authors M. Frehner, B. Quintal, N. Tisato, N. Riahi, C. Madonna, P. Sala, M. Kuteynikova and E. H. SaengerIdentifying and understanding the physical processes taking place in a reservoir rock is an important step towards a more detailed and accurate characterization of a subsurface hydrocarbon reservoir from a seismic data set, and is the subject of our article. We show that the integration of laboratory studies with numerical modeling is a powerful tool to achieve an unbiased comprehension of the physical processes at different scales. Such integration is demonstrated in this article using examples of two current challenges in rock physics: (1) understanding the influence of the rock microstructure on effective elastic properties; (2) identifying the dominant physical mechanism responsible for intrinsic attenuation in saturated rocks at seismic frequencies. In the first example, we show how the coupling between laboratory and numerical methods help provide a better understanding of the effect of the rock microstructure on the effective P-wave velocity. Additionally, this procedure enabled the numerical computations to yield an accurate prediction of the P-wave velocity with confining pressure. In the second example, we show that laboratory or numerical studies alone can lead to misconception or misinterpretation of the obtained results. A persistent combination of laboratory and numerical methods is essential for a successful rock physics research.
-
-
-
P-wave Dispersion and Attenuation in Patchy-saturated Rocks - White, Dutta, Johnson and Biot-Rayleigh Theories
Authors W. Sun, J. Ba, T. M. Muller, J. M. Carcione, H. Cao, Q. Du and X. YanThe P-wave attenuation and dispersion in fluid-saturated porous rocks are studied.A double-porosity saturation model is formulated based on the flow dynamics theory developed by Rayleigh, where the local fluid flow of a spherical inclusion is modelled. the Biot-Rayleigh (BR) theory is extended to the case of patchy-saturation rocks. The dispersion/attenuation curves of this method are compared with serveral previous theories. BR model shows better behaviour in fitting experimental data when inclusion size is at the same level of experimental diffusion length.
-
-
-
Determining Upper Bounds for the Clay-squirt Effect in Clay Bearing Sandstone
Authors M. K. Soerensen and I. L. FabriciusSonic measurements of saturated bulk moduli of clay bearing sandstones show larger values than expected by Gassmann modelling from dry rock properties. This causes difficulties in extrapolation of laboratory data to different saturants or frequencies. Squirt flow from the clay phase of the rock have been proposed as the mechanism behind this stiffening. Low fluid mobility and low bulk modulus of the clay phase cause excess pore-pressures to be induced and retained in the phase leading to stiffening. A quantitative bound is formulated for this effect through the determination of the Hashin-Shtrikman bounds for the case of a drained clay phase and an undrained clay phase. The bound is achieved by analyzing the influence of the relevant parameters with subsequent grouping using reasonable correlations. Through this approach only the saturated bulk modulus of the quartz phase and the clay fraction remain as free parameters. The bound is calculated for all possible values of these parameters. Experimentally observed values for non-Gassmann bulk modulus stiffening are found to fall below the bound for all values within the Hashin-Shtrikman bounds. Hereby this study shows that the clay-squirt effect may be the cause of observed stiffening.
-
-
-
Rock Physical Properties and CT Imaging of CO2-brine Displacement in Reservoir Sandstone
Authors Ø. Johnsen, B. Alemu, E. Aker and M. SoldalRecent CO2-brine drainage and imbibition experiments in natural sandstone reservoir analogue (23% porosity cylindrical Rothbach cored perpendicular to bedding, average permeability of 400 mD) demonstrate the implications of sub-core scale heterogeneity on fluid distribution of the involved phases and the associated geophysical response. The initially brine saturated specimen was drained by stepwise injecting liquid CO2, and changes in resistivity and ultrasonic velocity was monitored while simultaneously imaging the fluid distribution by an industrial CT-scanner. A similar procedure was subsequently used for re-imbibition with brine. The results indicate a close link between the response of the measured physical and the tomographically mapped minute saturation levels and provides a deeper understanding of the implications of the flooding and imbibition processes.
-
-
-
Constraining Reservoir Quality Predictions
Authors B. Moyano, E. H. Jensen and T. A. JohansenAn inverse rock-physics modelling strategy was used to provide estimates of reservoir parameters. Reservoir predictions made irrespectively of their spatial location, can have dissimilar ranges of variability. For instance, estimations of reservoir quality independently of their depths produced wide ranges of solutions, e.g. for lithology and saturation. Also a rock-physics calibration and model selection procedure using clay-rich siliciclastic data showed sets with wide ranges of solutions. Interdependency of parameters as porosity, lithology and saturation is expected and it can be used to constrain the model predictions, reducing the range of solutions and the uncertainty of the estimations. In this study, we use spatial correlation and observations which we have a higher level of confidence in to constrain predictions of the reservoir properties.
-