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76th EAGE Conference and Exhibition 2014
- Conference date: June 16-19, 2014
- Location: Amsterdam, Netherlands
- Published: 16 June 2014
1 - 50 of 1028 results
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Integration of Surface Seismic and Well Information to Improve Drilling Success for Onshore Carbonate Caves
SummaryOrdovician carbonate caves have been considered as important reservoirs for a long time and their exploration has rapidly increased in recent years in China ( Yang et al, 2010 ). Accurately locating the target is very critical to improve drilling success for carbonate caves. As carbonate reservoir exploration has moved deeper and deeper (6000–8000 m), wells often either hit the side of the cave or totally miss it. Here we look at the application of a new technology that is particularly suited to cave drilling. It initially builds an accurate baseline earth model; and then, during the process of drilling, it updates the subsurface image in real time by using information acquired while drilling in combination with surface seismic data. In this paper we show how this new technology can be used to help accurately reach deep carbonate caves.
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Full Waveform Inversion on the NW Shelf of Australia
Authors C.D. Manuel, G. Hampson, D. Chagalov, D. Bevc, T. Xu, B.J. Lim and D. VighSummaryA workflow for integrating full waveform inversion (FWI) with reflection tomography has been refined using narrow azimuth towed streamer (NATS) 3D seismic data from the North West Shelf (NWS) of Australia.
We show that FWI using relatively short offset NATS data with limited low frequency content can provide a high resolution velocity field if it is combined with reflection tomography in the workflow. Although other techniques exist for building an initial FWI model, reflection tomography was chosen here since a reasonably mature model was accessible from a project being run in parallel. Integration of reflection tomography and associated quality control (QC) practices into the time domain FWI model building sequence was found to be necessary to help the FWI converge to a satisfactory solution when turning ray energy was limited or non-existent. Investigation of typical FWI parameters was also necessary to refine each frequency update.
We also show comparisons of inversions for acoustic and elastic impendace from using FWI and reflection tomography data from this area.
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Predicting Multi-scale Deformation and Fluid Flow Patterns in Folds Using 3D Outcrop Models and Mechanical Modelling
Authors K. Bisdom, G. Bertotti and B.D.M. GauthierSummaryNatural fracture patterns in folded carbonates are highly heterogeneous. The present-day fractures are often the result of pre-folding, syn-folding and post-folding related fractures. Furthermore, syn-folding fractures may differ in different domains of the fold. Although there are studies that characterize fracture patterns in outcropping folds, there is still a poor understanding of the relation between large-scale deformation (i.e. folding), and small-scale deformation (i.e. fractures), especially in terms of stresses and process-based predictions of fractures. Our overarching goal is to assess the sensitivity of reservoir-scale flow to different fracture patterns and different fracture properties. Therefore we build multi-scale models of 3D fracture networks in outcropping folds in the foothills of the Tunisian Atlas (central Tunisia). The fracture data is collected from outcrops using efficient methods that collect both fractures and the 3D geometry of the outcrops. We interpret small-scale deformation in terms of stresses and combine this with fold-scale mechanical models to predict the fracture patterns in 3D throughout the fold. The 3D model is used to model fracture fluid flow. This work presents a new approach to outcrop studies, that distinguishes different stages of fracturing and uses stresses to make predictions about fracture patterns in similar structures.
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Natural Fracture Characterization in Aptian Carbonates, Araripe Basin, NE Brazil
Authors T.S. Miranda, J.A. Barbosa, J.F.W. Gale, R. Marrett, I. Gomes, V.H.M.L. Neumann, G.C. Matos, O.J. Correia and M.L. AlencarSummaryThis paper addresses fracture characterization in an Aptian laminated limestone, the Crato Formation, cropping out in the Araripe Basin (NE, Brazil) using a scanline technique. This unit has been used as a geological analogue of buried naturally fractured carbonate reservoirs. In recent years, studies of fractured reservoirs have drawn considerable attention due to their significance for oil production and enhanced recovery. The study was based on the use of traditional scanline surveys, and the recording of fracture orientation, morphology, crosscutting relationships, composition, texture of fracture fill, fracture aperture-size distribution (frequency), spatial distribution (coefficient of variation), and strain for each fracture set. The main fractures identified in the Crato Formation were shear- and opening-mode fractures (veins) and with stylolites also present. In this study we focus on opening-mode fractures, which strike in two main directions, NNW-SSW (set 1) and NE-SW (set 2), and are filled by recrystallized calcite. Fractures of set 2 have a wider kinematic aperture and spacing range and are more likely to be clustered than are fractures of set 1 (NE). These results have been used to populate computational models that consider the widespread fracture system in the geomechanical modeling of carbonate reservoirs.
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Controls on Failure Mode in Fractured Chalk, and Its Influence on Fracture Geometry
Authors M. Welch, R.K. Davies and R.J. KnipeSummaryThe mode of failure can exert a major control on the geometry of fractures in chalk: Mode 1 dilatant fractures are typically vertical, short, bed-bound but very closely spaced (20–50cm apart), whereas Mode 2 shear fractures are much longer, cut across bed boundaries, and form inclined conjugate sets, but are more widely spaced (1–3m apart). At Flamborough Head, northeast England, we see Mode 2 shear fractures formed in the lower Welton Chalk Formation but Mode 1 dilatant fractures in the overlying Burnham Chalk Formation. This will have a big impact on fluid flow through the two units: the Burnham chalk will have a high horizontal permeability but a low vertical permeability, whereas in the Welton Chalk horizontal permeability will be lower but vertical permeability higher. We use simple mechanical models to show that the failure mode in chalk is dependent on the depth of burial, mechanical properties, fluid pressure and mechanism of fracturing.
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Understanding the Interplay of Fractures, Stresses & Facies in Unconventional Reservoirs - Case Study from Chad Granites
Authors D. Lirong, C. Shrivastava, D. Chuanshu, W. Jingchun, N. Hammond, C. Anoliefo, D. Lei and M. SiddickSummaryThis work presents a a case study from Bongor basin, Chad which utilizes the geological evolution approach to effectively characterize unconventional granitic reservoir based on the interpretation performed with borehole images and open hole logs. Interplay of fractures and facies and the impact of the prevalent stress regime have been deciphered from the study wells with the help of borehole images and petrophysical logs. Three main distinct facies were interpreted; Unweathered, Leached and Fractured (Normal and Intensely Fractured sub-facies) granites respectively. Within the leached granite, there exist fault breccia and major faults with two dominant strike orientations; NE-SW and NW-SE. This resulted to the development of secondary porosity within these reservoir zones. The observed granite basement facies, particularly the fractured and leached granites developed good secondary porosity due to differential leaching and fracturing.
The placement of subsequent wells in the preferred leached and fractured reservoir facies bearing fractures that possess the same orientation as the maximum stress depends on several determinants, one of which is the location of the proposed well with respect to the prevalent stress regime attributed to tectonic forces from the Central African Shear Zone arising from the West and Central African Rift system.
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Structural Development of the Dutch Central Graben - New Ideas from Recent 3D Seismic
Authors E.A. Rosendaal, N. Kaymakci, D. Wijker and B.M. SchrootSummaryA regional study on the northern Dutch Central Graben (DCG) and Step Graben (SG) based on, amongst others, very recent regional 3D seismic data has resulted in new ideas on the structural development of the area.
It is postulated that main rifting of the DCG occurred during Middle to Late Triassic. The Late Jurassic extensional phases and the Early Cretaceous inversion phases affected the NS orientated DCG and SG in a different way than the NW-SE orientated basins. Under the NE-SW Late Jurassic extension, the NS bounding faults were not reactivated but WNW-ESE extensional faults developed creating a graben stepping down to the north. Furthermore, it seems that the Early Cretaceous inversion also did not reactivate the NS bounding faults but manifests itself only in a broad basin uplift with minor transpressional features.
Based on this regional work, we expect to improve our understanding of the timing of events, erosion amounts and paleogeography. We foresee future basin modeling to obtain further insights into the hydrocarbon maturation history. The observed WNW-ESE fault trends in the DCG could have tectonically controlled Late Jurassic to Early Cretaceous sedimentation and local accommodation space along the fault escarpments may create interesting opportunities for hydrocarbon exploration.
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Structural Framework Derived from Surface Satellite Data Integrated with Subsurface Gravity-seismic Imagery, SE Kenya
Authors D. Necea, M. Oehlers and N. JohnsonSummaryThis study reveals that surface satellite-derived structural results integrated with subsurface gravity and seismic imagery provides explorers a reliable assessment of the structural framework when searching for natural resources in new ventures, such as the Lamu Embayment, Kenya. This data integration shows that some of the surface faults extend at depth through the sedimentary covers as illustrated by the gravity contrasts and seismic interpretation. The NNW-SSE-trending and ENE-dipping normal faults are major basin bounding faults to N-S-oriented half-grabens and NNW-SSE-oriented Tana rifting zone, respectively. These bounding faults are probably Precambrian basement structures that were reactivated during subsequent tectonic events, e.g. Pliocene-Quaternary in the east. This age is inferred from NNW-SSE normal and ENE-WSW and WNW-ESE to NW-SE strike-slip faults, and fluvial networks affecting and incising, respectively, the Miocene-Quaternary deposits. The faults can delineate potential structural traps, e.g. uplifted footwalls of normal faults, roll-over anticline, which may be good traps for hydrocarbon accumulations. Present-day extension direction along the Kenyan coast is inferred as E-W in the south and ENE-WSW in the north. Analysis and conclusions of this study form part of the early stage of the area evaluation and need to be integrated with other datasets (FTG, seismic and more fieldwork).
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Geometry and Forming Mechanism of Synsedimentary Structures in Northern Melut Sub-Basin, South Sudan
More LessSummaryThe Melut Basin is a rift basin elongated in NW-SE direction located in south Sudan. Under the influence of Intracratonic extensional forces that resulted from the opening of the Atlantic, and associated left-lateral strike-slip, a series of synsedimentary structures are developed in Melut Basin. On the basis of different features of structure development continuous, late deformation and drive mechanism, there are mainly three types of synsedimentary structures developed, i.e. inherited structures, fault-related structures and differential compaction-related structures, respectively. Inherited structures are inherited from paleo-uplift and reformed by later-stage faulting. Fault-related structures form as a result of displacement decreases with distance from the fault surface caused by low dip angle listric fault. The origins for the listric fault include listric basin-bounding fault caused by adjacent titled block and strike-slip fault involved into shale formation. The main two types of differential compaction-related structures are caused by intense differential compaction within intervals of sandy conglomerate of alluvial fan and the original sediments are inclined to collapse into depression during sedimentary compaction, respectively. The synsedimentary fault and its assemble pattern controlled the distribution of sedimentary facies, the synsedimentary structures has great influence for the generation, migration, accumulation and preservation of oil and gas.
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Subtle Prospects Identification and Hydrocarbon Accumulation Model in Slope Zone, Rift Basin - A Case in Melut Basin
More LessSummaryTaking 3D seismic survey in Melut Basin for an example, we study the types and hydrocarbon accumulation model of subtle prospects in the slope zone controlled by palaeohigh in passive rift basin. Based on palaeogeomorpholgy restoration and sedimentary facies study, the subtle prospects contain the types of stratigraphic overlap and lithologic pinch-out in the zone, which mainly develop in the strong rift phase. The stratigraphic overlapping boundary can be identified by seismic attributes of Number of Zero Crossings, and the slump fans can be identified by seismic attributes associated with amplitude energy.
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Seismic Calibration of Distributed Acoustic Sensors (DAS) in a Joint Borehole-surface Experiment
Authors F. Poletto, A. Clarke, A. Schleifer, D. Finfer and P. CoruboloSummaryDistributed acoustic sensors (DAS) are an emerging fibre optic-based technology enabling seismic investigations with innovative configurations by massive receiver arrays in boreholes and at the surface. Advantages of DAS technology include lower equipment costs and reduced installation complexity, especially in boreholes, with respect to equivalent applications using conventional seismic sensors. We present results of a joint borehole-surface calibration experiment. The main targets of this study were the analysis of S/N and of the directional responses for recorded wavefields. Borehole signals were acquired by DAS and compared with signals acquired by permanent 3C geophones installed outside the casing of the instrumented well at maximum depth of about 200 m. Multi-offset vertical seismic profiles were acquired by a surface seismic vibrator source with two different azimuths. At the surface, settings of buried and near-surface sensors was prepared in a cross of trenches using DAS cables along with single and multicomponent geophones at corresponding positions. Using the surface installation, a reciprocal seismic line was acquired by maximum offset of approximately one kilometer for the vibrator source. The analysis shows the correspondences in the seismic wavefields acquired by the different methods, compares the physical quantities, and confirms the quality of the DAS signals.
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Seismic Data Analysis Using Digital Music Technology - Applications in Hydrocarbon Exploration
Authors P. Dell’Aversana, G. Gabbriellini and A. AmendolaSummaryWe introduce a novel approach for geophysical data processing, interpretation and integration. It is based on ideas and methods imported into the geosciences from the domain of sound analysis and digital music production. The presentation is divided in two main parts. First we introduce the theoretical and technical background. Starting from the already known concept of ‘sonification’ we derive other inedited ideas and methods. We explain how these are complementary and not substitutive of the methods currently used for geophysical data processing, imaging, and interpretation. In the second part, real applications of integrated imaging and sounding analysis addressed to hydrocarbon exploration are discussed.
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Benefit of Ultra-long Offset Data for Subsalt Imaging in Deep Water Gulf of Mexico
More LessSummaryIn the deep water Gulf of Mexico, wide azimuth (WAZ) data and the evolution of advanced imaging tools, such as TTI reverse time migration (RTM), have significantly improved the quality of subsalt imaging. By combining WAZ data with existing narrow azimuth data, imaging resolution is further improved.
However, subsalt imaging still remains difficult in areas with complex salt geometries, such as steeply dipping salt flanks and subsalt three-way closures. Full azimuth and long-offset acquisition is the latest acquisition technology to address subsalt imaging challenges. We analyze the impact of ultra-long offsets (up to 18 km) with 2D elastic modelling. Ultra-long offsets provide the ability to image steeply dipping subsalt events and undershoot complex salt geometry. With ultra-long offset field data extracted from a full azimuth survey, we also demonstrate that ultra-long offsets provide extra illumination power, helping image dipping subsalt events and improve the continuity of subsalt events in areas with complex salt geometry. Moreover, ultra-long offsets provide greater incident angle coverage in RTM 3D angle gathers, potentially aiding subsalt velocity updates.
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Optimal Survey Design for Big Data
Authors D. Coles, M. Prange and H. DjikpesseSummaryIndustrial geoscience is entering the age of ‘big data’, in which the data volumes routinely acquired for analysis are so large that they can no longer be processed by traditional workflows. How can we store and mine this deluge of information?
In this article, we focus on model-oriented design and analysis (MODA) -- the theory and practice of designing experiments to maximize the information expected in data observations. MODA is appealing because it is an optimization method, which offers confidence in the expected results, and because it can be applied before or after data acquisition, to either forecast the most informative data to acquire or to optimally select data from existing datasets. MODA reduces costs by increasing efficiency in either scenario, whether through data acquisition or data processing.
However, MODA is itself challenged by the computational demands of big data, and researchers are seeking ways to reduce its computational cost. One novel possibility is dimension reduction – especially if it is parallelizable. We develop a dimension reduction workflow for guided Bayesian survey design – a linearized MODA technique – that greatly reduces the computing cost of optimal survey design, and we demonstrate its utility on a real, industrial-scale marine seismic design problem.
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Energy Efficient Technologies of Hydrocarbon Resources Development
Authors M. Kotenev and A. KotenevSummarySubstantial deterioration of oil and gas reserves base is noted in many petroleum regions of the world. Improving the energy efficiency of resource extraction processes at any stage of the development of oil and gas fields is a priority. It is important to tactically and strategically plan all oil recovery technologies as early as at the initial geological study of the field. At different stages of field investigation a variety of techniques are being used for oil extraction modelling: physical, mathematical, geological-statistical. Special attention is given to the use of constantly operating geological and technological models for exploration and development control. Two example pilot projects for the Ural foredeep reef carbonate deposits in Russia and for the Mishrif formation at Zubair field in Southern Iraq justify prospectivity of comprehensive technology development of hydrocarbon exploration and production and have real life value. Suggested technical and technological solutions as use of existing facilities for gas injection, resuscitation of old wells, application of modern improved oil recovery techniques are aimed to reduce capital costs, create adequate development system which will allow to increase oil recovery on the depleted oil fields, increase work efficiency of gas distribution system during seasonal peaks of gas consumption.
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Logging While Drilling Via Autonomous Sonde
Authors A. Kepic, C.J. Dupuis, G. Stewart, B. Wilkinson, A. Greenwood and A. PodolskaSummaryWe present a method of geophysical logging while tripping drill rods to produce logs similar to wireline logs. The process is autinmous in that it does not require any significant changes by the driller and does not requie any modifications to the drill rig. Using starting depth, rod length, and sensors on the sonde a geophysical log can be created when the drill rods are retreived upon hole completion. Thus, thi smethodology is very suitable for slimhole and diamond drilling methods that do not case teh completed hole. Such holes often collapse and are too expensive to log via wireline logging.
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An Innovative Approach to Select Core Point in Challenging Environment Using the GWD&trade - (Gas While Drilling) Methodology
Authors A. Zaidi, C. Carugo, R. Pietrogiovanna and M. AliSummaryCore point selection plays vital role to ensure that cores are cut in best part of reservoir to fulfill objectives requested during well planning. Different methodologies are applied to select coring point. Depending on geological environment, these approaches reflect criticalities as rig time, offset of LWD tools, absence of markers etc. Here an innovative approach based on analysis of mud gas shows using GWD™ methodology is described. This methodology consists in computation of several ratios of hydrocarbon mixture (C1 to C5) continuously extracted from mud and monitored at rig site. A successful case history from a well recently drilled in Bhit field, Pakistan is presented. In this case, absence of drilling parameter changes and specific GR marker into thick shale sequence above reservoir does not allow proper identification of coring point. Gas data from two reference wells were analyzed and distinctive gas ratio trends between shale sequence and coring target were established, both qualitatively and quantitatively. After application of QC criteria, same trends were recognized in new well and coring point was selected even before scratching level of interest. Further confidence of quantitative aspects of methodology can lead to refine coring point selection, significantly saving rig time and costs.
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Multi-component 3D Seismic - A Successful Fracture Characterization in Algeria-Processing Challenges in Noisy Environment
Authors V. Belz, M. Donati, J.L. Piazza, S. Baillon, D. Marin, A. Rollet, H. Toubiana, J. Castro, C. Gordillo, A. Bouheouira, T. Belhouchet, A. Belbachir and M. RahalSummaryMulti-component recording in land environments usually suffers from high contamination by surface waves, together with low-frequency content. This, combined with severe problems of receiver statics and shear-wave splitting, can make the processing so challenging that the PS data provide a disappointing final result compared to PP data. However, it doesn’t need to be so: in this paper we show that a high level of noise in the raw gathers, doesn’t prevent us from obtaining final images as good as (if not better than) the more conventional PP datasets, provided that the processing sequence is carefully tailored to address this issue. We describe the main steps of the PP and PS-wave processing sequences, with a special emphasis on noise removal, and a PS-wave azimuthal anisotropy study at deep targets made possible by the cleaned-up and signal preserved pre-stack gathers.
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Multi-component 3D Seismic - A Successful Fracture Characterization in Algeria-Interpretation of Faults and Fractures
Authors J.L. Piazza, M. Donati, F.D. Martin, J. Castro, C. Gordillo, A. Bouheouira, T. Belhouchet, A. Müller, E. Ramia, S. Baillon, D. Marin and V. BelzSummaryThis paper describes the structural interpretation and the anisotropy analysis performed to characterize the fracture network using 3D-3C seismic data acquired as part of a 67km2 pilot survey in the Tin Fouyé Tabankort-West field located in the Illizi Basin in the Algerian Sahara. The target horizon corresponds to the Ordovician reservoirs composed of low porosity gas bearing sandstones located at a depth of approximately 1950 m below surface.
Well data show that the well performance is mainly controlled by the reservoir facies but faults and fractures are also thought to play a role in the gas production.
Based on a well controlled 3D-3C acquisition and a careful processing sequence of the PP and PS waves, this multi-component survey is proved to provide a better resolution of subtle faults and lineaments than the conventional 3D data seismic set available in the area even though the noise level remains slightly higher. Furthermore, the PS wave processing shows the evidence of shear wave splitting which is compensated to obtain an optimum radial component stack.
The PS wave anisotropy, found to be consistent with the faults and lineaments interpreted on the PP seismic data set and with the FMI information in the wells, is interpreted in terms of fractures.
The promising results of this 3D Multi-component seismic pilot provide an encouraging basis for wider 3D-3C acquisitions in areas where faults and fractures play an important role in the hydrocarbon production.
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3D-PS Converted Waves – Solving 3D-imaging Challenges under Gas Clouds - Offshore Malaysia
SummaryIn offshore peninsular Malaysia there are strings of major hydrocarbon bearing fields which are affected by shallow gas clouds. This poses a major problem in imaging using the P-wave data from conventional streamer or OBC 2C surveys which suffer from frequency dependent attenuation, multipathing, scattering, internal multiples, velocity inversions and mode conversions due to the gas charged sediments. 2D–4C data is proven to be useful in areas affected by shallow gas where 2D-PS-wave imaging provides clearer image as compared to 2D-P-wave imaging. Imaging of 3D-PS-converted-wave data presents its own unique challenges which discourage companies from processing the converted wave component of 3D–4C-OBC data. Through this case study we showcase three processes which have brought about significant improvements in the 3D PS-wave time-imaging and outline the results of 3D-PS-PSDM depth-migration, rendering the data to be highly useful for interpretation and inversion work inside the gas cloud affected area.
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Reconnaissance Processing to Understand Potential Value of Converted Waves - Experiences from Culzean
Authors A.S. Calvert, A. Merry, F.G. Bourgeois, E.S. Sturup-Toft, P. Salek, A. Rollet and S. PerrierSummaryThe focus of many ocean bottom seismic surveys is improved P-wave imaging using the hydrophone and vertical components. The horizontal components also record potentially valuable converted wave (C-wave) arrivals. The sensitivity of C-waves can provide insights into the rock properties and stress environment of not only the reservoir but also the overburden. C-wave processing projects often take significant time and sometimes produce disappointing results. We share our experiences conducting rapid reconnaissance processing to assess the potential value and challenges of conducting C-wave processing to constrain the geomechanical model of the HPHT Culzean Discovery. The geologic environment is conducive to obtaining high quality C-wave results although is more challenging beneath the top chalk. The full azimuth sampling available from the high density ocean bottom cable survey facilitates velocity analysis, assessment of shear wave splitting and illumination near a salt dome adjacent to the field. The shear wave splitting fast azimuth variations found in the shallowest layers are similar to the principle horizontal stress directions predicted from geomechanical modelling. Such evaluations can be conducted quickly and in parallel to fast track P-wave processing to allow early and more informed decisions about including the horizontal component data in the full production processing flow.
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Converted-wave Processing of an Ocean Bottom Cable Dataset from the Arabian Gulf
Authors M.J. Grimshaw, J.P. Holden, E. Murray, K. Shaukat, B. Beck and F. Al-EnaziSummaryThe processing of PS waves from a 4-component converted-wave dataset can provide complementary information to that obtained from traditional P-wave imaging. However, processing the PS component requires additional care to ensure the full potential of the data is realised. This paper discusses the specific processing required for a shallow-water converted-wave dataset acquired with an Ocean Bottom Cable (OBC) system in the Arabian Gulf.
Vector fidelity, receiver-side shear statics, and compensation for shear-wave splitting in the overburden are key topics that had to be addressed in the pre-processing. After further corrections for deeper shear-wave splitting, the PS data were regularised with differing schemes: for analysis of gamma-effective and pre-stack time migration velocity analysis; and for the migration of the data itself.
To maintain data integrity it was important to preserve the signal on both the radial and transverse components through all the processing steps up to and including migration. This ensured a final shear-wave splitting analysis could be made post migration at the target level to minimise any residual shear-wave splitting effects prior to final interpretation and in preparation for a joint PP-PS inversion.
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Shear-wave Splitting and Azimuthal Anisotropy in an Offshore Field in the Arabian Gulf
Authors J.P. Holden, B. Beck, M.J. Grimshaw, C. Giersz and F. Al-EnaziSummaryThe effect of shear-wave splitting, an expression of an azimuthal anisotropic medium, has been observed in shear-wave seismic reflection recordings since at least the 1980’s. Since those early experiments it has been recognised that the existence of this phenomenon will degrade shear-wave images unless the issue is addressed adequately within data processing.
A 4-component converted-wave dataset acquired in the Arabian Gulf exhibits such shear-wave splitting. Significant azimuthal anisotropy within the overburden, and locally in excess of 10%, results in a severe loss of coherency on the radial component. Correcting for the shear-wave splitting in this and subsequent intervals dramatically improves both the vertical and spatial resolution, and therefore the interpretability, of the data.
The resulting attributes from the analyses also yield information on the evolution of the subsurface. Of particular note is the overprinting of the azimuthal anisotropy in the post-Eocene overburden by the pre-Turonian (Cretaceous) faulted anticline. This is consistent with an interpretation of late uplift of this deep structure and the consequent extension of the overburden in a direction orthogonal to the structural axis.
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Elastic Impedance Minus Shear Impedance - A Powerful Pre-stack Inversion Attribute from OBC Data, Campos Basin, Brazil
Authors L.M.R. Martins and T. DavisSummaryPre-stack seismic inversion is a useful technique to predict the petrophysical properties of the reservoir. Using a four component (4-C) ocean bottom-cable (OBC) seismic survey we set out to improve the reservoir characterization in a deep-water turbidite field in the Campos Basin.
Elastic Impedance (EI) gives us the opportunity to calibrate and invert nonzero-offset seismic data, whilst acoustic impedance is useful for zero-offset data. On the other hand, shear impedance (SI) was derived from converted PS data in a pre-stack inversion process. EI in combination with SI inverted data produce a better characterization tool for fluid saturated reservoirs.
In this paper we combine EI and SI results from pre-stack inversion to better characterize the deep water turbidite reservoir.
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Dan Field Ocean Bottom Node (OBN) Survey - A Shallow Water Case History
Authors J. Zaske, P. Hickman, H. Roende, S. Mukund, S. Halliday and S. PerrierSummaryIn 2012 Maersk Oil acquired an Ocean Bottom Node (OBN) seismic survey over the Dan Field located in shallow water in the Danish North Sea. The survey took place shortly after a regional multi-field 4D monitor streamer survey which included the area around the Dan Field. The primary objective of the OBN survey was to acquire data in an area affected by surface infrastructure not accessible with streamer technology. Secondary objectives included evaluating the imaging results in comparison with streamer technology on a field wide scale and evaluating the matching quality between the vintage streamer and OBN survey data.
Significant challenges due to the shallow water environment were overcome during operations as well as processing. The results show a clear improvement with the OBN data in the area affected by the platforms when compared to the streamer data in-filled with conventional two boat undershooting. The OBN image is of a similar or better quality over most of the field when compared to the streamer result allowing for different strategic options for future seismic surveys in this area.
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Moveout Approximation for Converted Waves in Layered Orthorhombic Medium
More LessSummaryIn this work we study the hyperbolic moveout approximations for shear and converted waves in a layered orthorhombic medium with flat interfaces in the horizontal plane of symmetry, distinguishing two types of conversion - PS1 and PS2, with different shear polarizations. Note that the azimuthally dependent NMO velocity function for shear or converted waves is similar to that of compression waves - only the coefficients are different. Given a package of orthorhombic layers with different parameters, one can establish an equivalent effective model consisting of a single layer with the same vertical time as the original package, described by the fast and slow effective NMO velocities, the effective azimuth of the slow velocity, and the vertical compression velocity. The latter is normally obtained from non-seismic information such as check-shot or well logs. Note that the effective azimuths are different for models describing PP, PS1 and PS2 waves.
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General Definition of Reflection-point Coverage for P- and PS-wave COV Data
By J.E. GaiserSummaryCommon-offset vector (COV) data have served industry well for survey design, generating well-sampled datasets for noise suppression, offset and azimuth analyses and inversion, and image improvements. For P-waves acquired on a flat recording surface, the basic cross-spread theory assumes that reflection-points (RPs) occur below common mid-points (CMPs). This assumption is ray-based, for 3D propagation in isotropic laterally homogeneous media. However, converted P- to S-waves (PS-waves) and other geometries violate this theory because of their asymmetric ray paths. In this paper I apply a general ray-based theory to define COV illumination area for both P- and PS-waves of various geometries. This involves a first-order approximation in ray-parameter, p, of reflection-point (RP) position as a function of t0V2 terms: vertical traveltime and NMO velocity. This definition facilitates corrections to improve RP consistency within a COV gather or volume. I describe corrections applied to offset-vector tile (OVT) distortion for conventional land orthogonal cross-spread data, and for marine geometries of ocean-bottom cable and node (OBC and OBN) geometries where source and receiver have a different datum. Also, I show that this theory can be applied to illumination distortion from structure (plane dipping layers) and discuss corrections for COV data in the context of migration.
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Model Based Registration of PP and PS Waves in the Depth Domain
More LessSummaryWe introduce an approach to perform a model based PP and PS registration in depth domain which involves converting the RMS time model to the depth model and performing PSDM. We have developed a GUI tool for depth model building and a PSDM tool which is based on the ray-tracing method and Kirchhoff summation. This approach is applied to a real 2D dataset. Time processing is applied to the PP and PS waves to obtain time images and RMS velocity models separately. Then the depth models are obtained for the PP and PS waves. For PS waves, we build the depth model as close to the P wave depth model as possible. Finally, we apply the prestack depth migration to produce migrated depth images. The results show that the events in PP and PS depth images are well correlated. The model building in this approach is straightforward and this approach is practical.
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S-ray Approximation Tomography for PP and PS Horizon Co-Depthing
Authors L.A.D. D’Afonseca, M. Dumett, O.J. Birkeland, P. Guillaume, T. Krishnasamy, T.M.G. Santiago and C. GuerraSummaryDepth imaging of multicomponent data involves additional challenges of event registration and co-depthing. Marine multicomponent data usually comes from ocean bottom cable (OBC) or ocean bottom node (OBN) acquisitions. Therefore, two data sets need to be processed: P-waves (PP) and converted waves (PS). A P-velocity model can be built with techniques similar to the conventional streamer data processing, but the S-velocity demands special treatments. We propose a method for estimating P- and S-velocities by simultaneously inverting PP and PS seismic reflection residual moveout data and matching PP and PS horizons to well markers in a TTI anisotropic medium. We present a work flow to update the Vs component of a TTI velocity model using a tomographic co-depthing of PP and PS horizons based on an S-ray approximation for PS-horizon map migration. This method is integrated to tomography and allows fitting PP and PS residual moveouts simultaneously to horizon matching. Field data shows that this strategy yields more realistic velocity models than those obtained by simple 1D velocity model updates, providing depth images of superior quality.
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PS-wave Processing and Velocity-model Building from a Sparse OBN Array
Authors R.R. Haacke, L. Casasanta, P. Chiarandini, N.V.V. Golla, A. Kalil, S. Drummie, I. Meades and A. StrudleySummaryPS-wave processing is particularly challenging for sparse ocean-bottom acquisitions in deep water. Problems in signal processing revolve around the extreme asymmetry of raypaths (due both to the mode conversion and also to the acquisition geometry), as well as severe aliasing and low fold in conversion-point gathers that would be well focused with denser acquisitions. Aliasing and low fold also cause problems in PS-wave velocity-model building, since migrated gathers are typically noisy and multidimensional interpolation or regularisation methods produce inaccurate images in the shallow subsurface. These problems require methodological modifications both in the processes applied and in the workflows with which they are implemented. For example, PS-wave directional-designature and surface-related multiple suppression are particularly effective with receiver-domain radial-down deconvolution. Meanwhile, meaningful updates of principle shear velocity and anisotropy without use of image gathers for tomography or quality control can be achieved using common-receiver controlled-beam migration straight to stack. Examples from data acquired in deep water to the west of the Shetland Isles (UK) show the efficacy of such modifications, and indicate that PS data from such sparse acquisitions can provide useful images of the subsurface.
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Application of Excitation Amplitude Imaging Condition to PS Wave Imaging in Elastic Reverse-time Migration
Authors Q.Z. Du, M.Q. Zhang, X.F. Gong and Y. LiuSummaryFor reverse-time migration, the imaging condition is one of the key factors that will not only determine the image quality but also influence the storage cost and computational efficiency. In this paper, we extend the highly-efficient and well amplitude-preserved excitation amplitude imaging condition from acoustic reverse-time migration to elastic reverse-time migration. In this paper, we firstly provide the detailed realization process of this imaging condition in elastic reverse-time migration. Considering the polarity reversals in PS image, we then propose an innovative way to combine the polarity reversal correction method with this imaging condition in PS wave imaging. Numerical examples demonstrate that this imaging condition is well amplitude-preserved and can obtain polarity-consistent PS image of comparable quality to that of source-normalized crosscorrelation imaging condition. Meanwhile, the disk occupation can be almost negligible and the computational efficiency is highly improved compared with those of crosscorrelation-based imaging conditions.
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Near-surface Imaging Challenges for Marine PS-wave Data
Authors L. Casasanta and S. GraySummarySparse seafloor seismic acquisitions present new challenges when processing and imaging converted wave (PS-wave) data. The severe anti-symmetric nature of PS-wave reflections for deepwater acquisitions, and the strong aliasing and low fold derived from sparse shot or receiver arrays, necessitate the solution of significant practical problems to achieve high-quality seismic images near the seafloor. The problems of PS-wave imaging with deep-water, sparse ocean-bottom receiver arrays (OBN or OBC) has motivated new investigation and led to interesting results.
For sparse acquisition geometries, wavefield aliasing is more acute when processing in some domains than others. For example, shot-carpet acquisitions recorded with sparse ocean-bottom nodes are well sampled in the common-receiver (CR) domain but poorly sampled in the common shot (CS) domain. Migration of these data is more attractive in the CR domain, in which the process of anti-aliasing during migration may be more effectively carried out than in the CS domain. Nevertheless, the summation of all the migrated CR wavefields still suffers from aliasing caused by the large receiver spacing. Further, low S-wave velocities are responsible for narrow illumination cones for all the CR migrated images, and the coarse receiver spacing cannot “heal” these images to produce a coherent stacked image near the seafloor. Here we propose some practical solutions to mitigate the effects of receiver spacing. We use Gaussian beam migration (GBM) to track surface ray parameters into the subsurface. We use this information both to redatum CR recorded wavefields above the seafloor and to anti-alias CR migration. Also, we show that PS-wave common-offset-vector (COV) GBM can provide adequate anti-aliasing when the receivers are relatively close together (OBC). Synthetic examples illustrate the effectiveness and limitations of these solutions for both OBC and OBN data.
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Wavefield Decomposition of Field Data, Using a Shallow Horizontal Downhole Sensor Array and a Free-surface Constraint
Authors N. Grobbe, J. van der Neut, C. Almagro Vidal, G. Drijkoningen and K. WapenaarSummarySeparation of recorded wavefields into downgoing and upgoing constituents is a technique that is used in many geophysical methods. The conventional, multi-component (MC) wavefield decomposition scheme makes use of different recorded wavefield components. In recent years, land acquisition designs have emerged that make use of shallow horizontal downhole sensor arrays. Inspired by marine acquisition designs that make use of recordings at multiple depth levels for wavefield decomposition, we have recently developed a multi-depth level (MDL) wavefield decomposition scheme for land acquisition. Exploiting the underlying theory of this scheme, we now consider conventional, multi-component (MC) decomposition as an inverse problem, which we try to constrain in a better way. We have overdetermined the inverse problem by adding an MDL equation that exploits the Dirichlet free-surface boundary condition. To investigate the successfulness of this approach, we have applied both MC and combined MC-MDL decomposition to a real land dataset acquired in Annerveen, the Netherlands. Comparison of the results of overdetermined MC-MDL decomposition with the results of MC wavefield decomposition, clearly shows improvements in the obtained one-way wavefields, especially for the downgoing fields.
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Pore-scale Analysis of Electrical Properties in Laminated Rock Using Digital Rock Physics
More LessSummaryA significant percentage of the world’s estimated hydrocarbon reserves are contained in thinly layered reservoir formations. In order to analyze the electrical properties of laminated rocks, a laminated digital rock is reconstructed via process-based method. Then a finite element method special designed to analysis the electrical properties of porous media is imposed on the model. Differing from the electrical properties of homogenous rock, the RI-Sw curve of laminated rock does not show a linear relationship, due to the bedding effect and anisotropy. The RI-Sw curve can be divided into two linear segments with different saturation exponent. The first segment with lower slope is at high value of water saturation, and the second one with higher slope is at low water saturation. If we take the capillary pressure into consideration, the first segment of RI-Sw curve with low value of slope should correspond to macro-porous layers and the high slope segment should correspond to the micro-porous layers. Traditional Archie equations cannot well describe the electrical behavior of laminated rock partially saturated with formation water. Therefore, the electrical behavior of laminated rock should be considered in calculating water saturation.
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Numerical Estimation of Carbonate Properties Using a Digital Rock Physics Workflow
Authors M. Osorno, D Uribe, E.H. Saenger, C. Madonna, H. Steeb and O. RuizSummaryDigital rock physics combines modern imaging with advanced numerical simulations to analyze the physical properties of rocks. In this paper we suggest a special segmentation procedure which is applied to a carbonate rock from Switzerland. Starting point is a CT-scan of a specimen of Hauptmuschelkalk. The first step applied to the raw image data is a non-local mean filter. We then apply different thresholds to identify pores and solid phases. Because we are aware of a non-neglectable amount of unresolved micro-porosity we also define intermediate phases. Based on this segmentation determine porosity-dependent values for the p-wave velocity and for the permeability. The porosity measured in the laboratory is then used to compare our numerical data with experimental data. We observe a good agreement. Future work includes an analytic validation to the numerical results of the p-wave velocity upper bound, employing different filters for the image segmentation and using data with higher resolution.
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Quantitative Investigation of Microstructures within Porous Rocks by Using Very High Resolution X-ray Micro-CT Imaging
Authors G. Zacher, M. Halisch, P. Westenberger and F. SiekerSummaryToday’s high-resolution X-ray CT with its powerful tubes and great detail detectability lends itself naturally to geological and petrological applications. Those include the non-destructive interior examination and textural analysis of rocks and their permeability and porosity, the study of oil occurrences in reservoir lithologies, and the analysis of morphology and density distribution in sediments – to name only a few. Especially spatial distribution of pores, mineral phases and fractures are important for the evaluation of reservoir properties. The possibility to visualize a whole plug volume in a non-destructive way is undoubtedly the most valuable feature of this type of rock analysis and is a new area for routine application of high resolution X-ray CT. All presented geological CT volume evaluations were performed with GE’s phoenix nanotom, a 180 kV/15 W nanofocus CT system tailored specifically for extremely high-resolution scans of samples weighing up to 3 kg and with voxel-resolutions down to < 300 nm.
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Uncertainty Quantification in Rock Physics Modelling
By D. GranaSummaryRock Physics describes how reservoir rock properties, such as porosity and mineralogy, affect elastic properties, such as seismic wave velocities. If the rock properties are known, then we can predict the corresponding elastic properties and the seismic response using a rock physics model. Since measurements of rock properties in the reservoir are uncertain, we propose to apply rock physics models to random variables rather than deterministic values. If the input random variable can be described by a probability distribution, then we can formulate a probabilistic approach to rock physics models to estimate the exact probability distribution of the rock physics predictions. In this paper, we present the probability theory of this new approach, the application to two common models, such as Gassmann’s equation and Raymer’s relation, an illustrative example and a real case study.
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Constraining Petrophysics with Rock Physics
By M. SamsSummaryIn the context of seismic reservoir characterisation the availability of high quality and consistent petrophysical analysis is essential. Achieving consistency is often compromised by poor data quality, lack of sufficient data and ambiguities in the data. Rock physics modelling can help to improve the consistency by ensuring that the petrophysical interpretations are also constrained by the elastic logs. There are three ways that rock physics can be used. First as a simple quality control, second to provide quantitative feedback to the petrophysics and third in a joint interpretation. The choice of method depending on the confidence achieved in the rock physics model.
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Combined Modeling of Burial History and Rock Physics Properties - A Barents Sea Demonstration
Authors P. Avseth, I. Lehocki and T. VeggelandSummaryIn this study we show how we can combine basin modeling principles with rock physics models. We apply the Walderhaug diagenetic modeling approach to simulate porosity and rock texture evolution during geological time, and use these as input to contact theory rock physics models which allows us to predict seismic properties as a function of the burial history. We also demonstrate how this approach can be used to estimate tectonic uplifts, and show an example from the Barents Sea.
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Unlocking the Secrets of Seismic Anomalies in the Load Transfer Domain
Authors A.S. Selnes, A.E. Edwards, N.W. Whitfield, K.W. Waters and C.M. MarzocchiSummaryWe will in this paper describe the importance of how integration of elastic properties and pressure is essential in order to better understand and constrain AVO signatures in the sub-surface, and particularly how amplitudes in the load transfer domain may differ from what is expected at a given prospect level, and thus may be overlooked as false negatives if not accounted for. This is particularly important in a regional context for exploration purposes (e.g. regional studies).
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Temperature Gradient Anomalies in the Buntsandstein Sandstone Reservoir, Upper Rhine Graben, Soultz, France
Authors S. Haffen, Y. Geraud, M. Diraison, C. Dezayes, D. Siffert and M.H. GarciaSummaryThe geothermal reservoir at Soultz-sous-Forêts is targeted in a granite horst bounded by subvertical normal faults. Exploration and production results tend to show that the Buntsandstein formation, made of inter-bedded sandstones and argillite in the Rhine Graben, above the granitic basement, may also have geothermal potential. Indeed, temperature gradient anomalies observed in the Buntsandstein indicate that the Buntsandstein could be exploited to produce heat or even electricity. In order to determine the fluid flow pattern within the sandstone formation, we compare two temperature gradient logs: on the one hand, the observed gradient log derived from temperatures measured along a borehole, on the other hand, a calculated one based on thermal conductivities measured on borehole cores. The observe temperatures gradients anomalies, could be explained by fluid flow patterns, thus phenomenological study has been carried out using TOUGH2 to simulate fluid flow and heat transfer for various boundary conditions. These results allow building a conceptual model (980–1400 m) of the sedimentary reservoir above the granitic basement at Soultz-sous-Forêt.
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Realistic DFN Modelling Using 3D 3C Seismic Data for the Marcellus Shale with Application to Engineering Studies
Authors S.J. Emsley, S. Chi, J. Hallin and J. RivasSummaryThe development of resource plays is moving on from drilling on a regular grid; but it is not sufficient to ‘simply’ identify a sweetspot in a resource play. It is also necessary to understand connectivity and compartmentalisation, this may be achieved through the development of a realistic fractured reservoir model. Seismic data volumes, inversion studies and rock physics provide a wealth of information covering reservoir intervals. Co-rendering of the data volumes leads to a more easily interpretable image of the subsurface and a better understanding of the reservoir. This paper discusses the construction of a realistic DFN model that was built using inputs derived from a 3D multi-component seismic dataset, seismic attributes, anisotropy information, seismic inversion results and well data. As model incorporates the seismic data deterministically the DFN can be used to guide well placement and planning, predict inter-well connectivity and can be used to forward model completions in terms of fracture generation or reactivation and micro-seismic event generation.
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Fracture and Carbonate Reservoir Characterization Using Sequential Hybrid Seismic Rock Physics, Statistic and Artificial
By D. HasanusiSummaryTiaka field is located in the Senoro-Toili block at the eastern arm of Sulawesi, Indonesia. The main hydrocarbon bearing reservoir is a lower Miocene carbonate sequences which posses a dual porosity system both matrix and fracture. This carbonate complexity is required special treatment to precisely characterize the reservoir.
In this paper, the latest technology for carbonate complex reservoir characterization using hybrid seismic rock physics, statistic and artificial neural network will be presented. This methodology enable in integrating a huge size of various data set to produce “coherence correlation” among input data and their target. The data set consist of core, electric logs, multi-attribute either pre-stack or post-stack of a 2 D seismic lines and seismic rock physics. The whole input data was trained using workflow and combined with statistic and artificial neural network to predict reservoir parameters.
This method is applied to predict the lateral lithofacies, fracture, porosity, fluid or hydrocarbon distribution. By using these approach, its can produce high accuracy on the reservoir parameter prediction. The accuracy of testing process show that predicted parameter reservoir on the average 90 percent matched reservoir parameter in the existing wells.
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Identification of Facies from Multiple Well Logs Accounting for Spatial Dependencies and Convolution Effects
Authors D.V. Lindberg, E. Rimstad and H. OmreSummaryFacies identification from multiple well logs is performed in a case study on a pair of wells from a reservoir offshore Norway. The inversion is cast in a Bayesian setting, with spatial dependencies in the facies enforced in the prior model by a Markov chain assumption and with possible convolution effects accounted for in the likelihood model. The proposed method outperforms a simpler model without these two properties in terms of correct facies classification, with more reliable predictions especially on layer thickness.
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An Innovative Approach for Formation Fluid Typing with API and GOR Assessments in Real Time from Mud Gas Data
Authors D. Merino-Garcia, G. Beda, J. Dessay, A. Nouraei and B. LovattiSummaryRepsol Sinopec Brasil has refined the operational methodology to quantitatively determine methane to pentane composition from mud gas, establishing good matches with the laboratory PVT gas data.
Deriving hydrocarbon reservoir fluid properties, from mud-gas data while drilling, is an attractive perspective. The proposed methodology includes an in-house mathematical model with:
- Two parameters (alpha and beta) to describe the composition of the hydrocarbon fluids, except those that are altered by secondary processes.
- Mud gas ratios and delineation of alpha-beta regions to predict fluid type, API and GOR in ranges adequate for operational decisions. Prediction is enhanced by tuning to regional data.
Two examples from offshore Brazil are presented as proof of concept, a gas reservoir from the “post-salt” turbiditic deposits and a rich gas condensate reservoir from the “pre-salt” carbonates. Real time evaluation of fluid typing, GOR and API is illustrated by a “post-salt” appraisal well.
This new approach has a significant impact at the exploration and appraisal drilling stages. Early fluid type identification with API and GOR assessments can be integrated into the objectives of the fluid sampling program from wireline. More important, it helps to properly design the well testing at an early operational phase.
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Carbonate Seismic Rock Physics Modeling and Hydrocarbon-detection
Authors Y.J. Zhou, X.H. Zhang, Y. Lei, H.S. Sun and Z.G. HeSummaryCarbonate reservoirs accounted for more than 50% of total reservoirs worldwide, however, the carbonate reservoir is characterized by complex structure and strong heterogeneity, seismic reservoir characterization is facing enormous challenges. This paper focuses on the dolomite reservoir of Majiagou formation in Jingbian gas field, Changqing Oilfield, the biggest oilfield in China. Through analysis of amounts of drilling, logging and testing data, the author clarify the key factors affecting the velocity of dolomite. For the first time the empirical equations of Vp, Vs and dolomite’s density, shale content (Vsh) and gas saturation were established for the study area. The sensitive factors of lithology and fluids are selected. With prestack simultaneous inversion and cross plots of sensitive factors, the most prospective area was selected and has been proved by the drilling results. Through this study, the technology of seismic characterization for dolomite has been set up.
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Integrated Reservoir Modelling Workflow for Deep Water Turbiditic Reservoirs - An Angola Case Study
Authors G.B. Straathof, C. Rigollet, F. Ferdinandi and G. SpregaSummaryAngolan deep water offshore is one of most prolific area for hydrocarbon exploration and production. The main discoveries are in high sinuosity turbiditic channels of Miocene and Oligocene age, deposited in slope valley corridors. The large amounts of sediments sourced from the African margin and the high energy level of the depositional environment create numerous discontinuities at regional and local scale, producing complex sedimentary structures ( Anka et al. 2009 ). The heterogeneities inside the reservoir impact the connected volumes and reservoir fluid path.
The paper describes a reservoir modelling workflow developed to simulate the reservoir architecture and analyse the uncertainties related to reservoir connectivity for a small oil field offshore Angola. Fluid path discontinuities above and below the corridor scale were split and managed with an innovative approach. A deterministic geological concept for the channel complex valleys was established to drive the seismic interpretation. Individual slope valley corridors mapped on the seismic provided the framework for the reservoir architecture and the facies simulation. Sub-corridor discontinuities were subsequently treated in a probabilistic way generating multiple realizations closing the data uncertainty gap. The result of this integrated workflow provides a reliable reservoir model appropriate for field development planning and reservoir management.
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Reservoir Characterization Using Converted-wave Seismic Data - Case Study from Athabasca Oil Sands
Authors C. Dumitrescu, G. Larson, F. Mayer and D. TalingaSummaryThe Lower Cretaceous McMurray Formation reservoir used in this study is located in the Athabasca basin, of the Northern Alberta, Canada. High resolution multicomponent 3D seismic data, along with core and well data were processed using the most advanced workflows in order to image the reservoir heterogeneity. These workflows include petrophysical analysis, joint PP-PS inversion and neural network analysis. Three inversions using PP and PS seismic data are analyzed and compared. The joint PP-PS inversion of the prestack seismic data produces the best estimates of P-impedance, S-Impedance and density, allowing for excellent reservoir characterization.
Neural network analysis is used to enhance the resolution of the elastic properties estimated from joint PP-PS prestack inversion, and to estimate petrophysical and engineering properties such as porosity, resistivity and saturation. In all neural network analyses the most significant seismic attributes include converted-wave information.
Some of the results are: 1. converted-wave seismic data have a major role in oil-sands reservoir characterization; 2. estimated density seismic volume shows a good separation of the two bitumen sands; 3. P-wave velocity seismic allows better mapping of the McMurray top; 4. estimated resistivity allows not only to differentiate the reservoir from the non-reservoir but also bitumen sand from water sand.
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A New Solution to Eliminate Free Surface Related Multiples in Multicomponent Streamer Recordings
Authors M. Vasmel, J.O.A. Robertsson and L. AmundsenSummaryWe present a new method for the elimination of free surface related multiples in marine seismic data. The method can be applied to datasets that contain both pressure and vertical component of particle velocity recordings. It is based on using a time domain finite difference propagator to generate equivalent data that would be recorded if the free surface above the source and receiver level were replaced by a halfspace with the properties of the water layer, so that all upgoing events radiate outwards instead of being reflected by the sea surface. The interaction with the unknown subsurface geology is taken into account through the use of exact boundary conditions along the acquisition level where we use the recorded data as Green’s functions.
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Generalization of the EPSI Primary Estimation Algorithm for Deep-towed and Slanted Cables
More LessSummaryProperly removing the ghost effect for deep-towed and slanted cables is a non-trivial task, due to the strong notch effects of such geometries. However, processing steps like surface-related multiple elimination (SRME) and the recently developed estimation of Primaries by sparse inversion (EPSI) algorithms require ghost-free data as input. Therefore, EPSI is redefined to invert directly for the primaries without the ghost, while the input data has ghost effects. In this way the deghosting process becomes part of the inversion scheme and can be optimally handled. It will be shown that it is possible to extend the EPSI algorithm for handling ghost from deep-towed and even slanted cables.
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