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77th EAGE Conference and Exhibition 2015
- Conference date: June 1-4, 2015
- Location: Madrid, Spain
- Published: 01 June 2015
21 - 40 of 980 results
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Coquina Carbonate Reservoir Analogues - Key Learnings from the Cretaceous, NE Brazil, and the Holocene, W Australia
Authors P. Corbett, R. Estrella, A. Morales, A. Shoeir, L. Borghi and A.C. TavaresCoquinas are important reservoir units in Pre-Salt reservoirs of the Southern Atlantic. The Cretaceous Morro do Chaves, onshore NE Brazil, has long been considered an analogue for the reservoirs. The Holocene coquina deposits accumulating at the southern end of Shark Bay, Western Australia, have also been proposed as an analogue. In this paper, new petrophysical data from the Cretaceous outcrop have been combined with training images from the Recent analogue to produce geoengineering models for use in reservoir simulation models to understand possible reservoir engineering signatures. In this paper we discuss the learnings that come from these outcrop studies and show how they might be utilised in reservoir characterisation and upscaling studies of coquina reservoirs to improve understanding of reservoir behaviour.
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Coupled Approach Using Stratigraphic Modeling and Seismic Inversion to Enhance Carbonate Reservoir Characterization
Authors C. Pellan, M. Zen, N. Rodriguez Morillas, T. Ait-Ettajer and L. FontanelliA successful exploration well leading to an economically valuable discovery, kick off new challenges for the Appraisal phase and future development of the field, especially in carbonate environment where spatial continuity of facies can be limited. A phase of detailed reservoir characterization is starting, where bringing tools and concepts from exploration at lower scale and higher resolution can add value to classical methods. In this framework, results of 4D Forward Stratigraphic Modeling combined with Seismic Inversion can be a useful tool to assess spatial boundaries of facies, and thus optimize well number and location on a reliable basis. The high resolution reached by stratigraphic modeling in low transport carbonate environment is bringing added value to the coarser resolution of seismic interpretation, and Acoustic Inversion. It is also integrating the very high resolution but spatially irrelevant well information. Thus, a high level of detail regarding the reservoir composition is reached, taking into account sequence stratigraphy principles. Furthermore the common and coherent features observed by two radically different approaches (Inversion form seismic data, and forward stratigraphic modeling) are strengthening the reliability of both techniques.
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Combined Rock-Physical Modelling and Seismic Inversion Techniques for Characterisation of Stacked Sandstone Reservoir
Authors A. Justiniano, M. Jaya, G. Diephuis, R. Veenhof and T. PringleThe objective of the study is to characterise the Triassic massive stacked sandstone deposits of the Main Buntsandstein Subgroup at Block Q16 located in the West Netherlands Basin. The characterisation was carried out through combining rock-physics modelling and seismic inversion techniques. The application of inversion on time-converted PSDM stack results in better seismic impedance resolution due to better well-seismic match performance. The results show that even though the Bunter reservoir consists of lithologically uniform massive stacked sandstones, the obtained rock property volumes allow distinguishing two zones within the target unit. The upper zone - Hardegsen and Detfurth Formations - exhibits on average lower acoustic impedance, shear impedance and bulk density values compared to the lower zone - the Volpriehausen Formation. These differences are essentially attributed to changes in porosity. Larger porosities make these rock properties decrease. Moreover, it is believed that locally the entire Bunter reservoir is gas-bearing, but the Volpriehausen sandstones are tighter. Vp/Vs ratio and Poisson’s ratio are good gas-fluid indicators. Both decrease for Bunter reservoirs compared to shales of the Solling and Rogenstein Formations. Furthermore, the rock property volumes allowed improved mapping of top and base of the Bunter reservoir compared to the original seismic reflectivity volume.
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Closed-Loop SRME with Data-reconstruction
Authors G.A. Lopez Angarita and D.J. VerschuurTo obtain an accurate surface multiple estimation via data-driven methods, dense source and receiver sampling is required. The traditional approach to this problem consists in performing data interpolation prior to multiple estimation. Though appropriate in many cases, this methodology fails when big data gaps are present or when relevant information (e.g. near-offset data in shallow-layer environments) is not recovered. We propose a solution in which multiple estimation is performed simultaneously with data reconstruction. For this purpose we propose to extend the recently introduced Closed-Loop SRME (CL-SRME) algorithm to account for the primary estimation in the case of coarsely sampled data. This is achieved by introducing a focal domain parameterization in a sparsity-promoting CL-SRME method. This algorithm will show its capacity to reconstruct large data gaps and provide reliable primary estimations, even in the presence of large under-sampling and missing near offsets.
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Finite Difference Modelling with (2M)Th-order Spatial and (2N)Th-order Temporal Accuracies for 2D Acoustic Wave Equation
More LessWe develop the method introduced by Liu et al. from (2M)th-order accuracy both in space and time domain to (2M)th-order accuracy in space and (2N)th-order accuracy in time, by which we can save a lot of computational cost without decreasing the accuracy. The dispersion and stability analysis show that the new stencil with (2N)th-order temporal accuracy can obtain smaller dispersion, greater accuracy and better stability than the conventional stencil. Increasing the number of points off the axial in the new stencil can further increase the temporal accuracy but this also increases the computational cost. By utilizing the new stencil, a larger time sampling interval can be used while maintaining the accuracy. Therefore some N and some time sampling interval can be used to achieve the smallest computational cost while maintaining the accuracy. Modelling examples demonstrate the advantage of the new stencil over the conventional stencil.
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Converted Wave RTM Using Lowrank Wavefield Extrapolation
Authors L. Casasanta, Z. Xue and S.H. GrayAlthough wavefield extrapolation techniques are well developed for P-wave seismic imaging, ray based migration algorithms are still the workhorse for converted-wave (PS-wave) depth imaging. Full (exact) elastic-wave reverse-time anisotropic migration (RTM) has not been widely adopted for reasons of computational and workflow efficiency, despite its potential to deliver accurate sub-surface images in complex geological settings by directly solving the elastic wave equation. Even (approximate) converted-wave RTM in anisotropic media, using separate finite-difference propagators for quasi-P and quasi-S waves, is limited in applicability for algorithmic reasons. Here, we introduce an alternative converted-wave anisotropic RTM, using a low-rank decomposition of mixed-domain space-wavenumber propagators for quasi-P and quasi-S waves. These operators are formal integral solutions of the pure-mode wave equations which guarantee stable and dispersion-free time extrapolation for coarse time steps in anisotropic, heterogeneous media. The pure-mode extrapolators are attractive for both PS-wave structural imaging and velocity analysis. An ocean bottom cable synthetic example illustrates the effectiveness of low-rank PS-wave RTM when compared against state-of-the-art Gaussian beam and finite difference RTM algorithms.
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Curvelet-based 3D Reconstruction of Digital Cores Using POCS Method
More LessWith the development of shale-gas exploration and exploitation, it is necessary to study the 3D spatial distribution of shale fractures for research on shale rock physics. Because of limitations of instruments, accurate shale slice is discontinuous in depth, and the minimum interval between adjacent slices in depth is inconsistent with horizontal resolution of digital cores. Those are the main factors which can prevent accuracy improvement for fracture characterization and physical modeling of digital cores. In order to study the 3D spatial distribution of fractures, this abstract achieves reconstruction of 3D digital cores using Project Onto Convex Sets (POCS) method in curvelet domain. Tests on sand dataset obtained from X ray scanner and accurate shale rocks obtained by focused ion beam scanning electron microscopy (FIB-SEM) demonstrate the validity and superiority of the proposed method.
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Brittleness Index Research Based on the Anisotropic Seismic Rock Physics for Tight-oil Sandstone
Authors X.R. Huang, J.P. Huang, Z.C. Li, Z. Guan and Y. YangCurrent seismic rock physics model for tight sandstone is not sufficient to depict its complicated microstructure. In this paper, we build a seismic rock physics model from five aspects which are clay type, filler content, pore connectivity, pore type and vertical fracture. The new Brittleness index is established based on the new rock physical model. In order to detect the superiority of the new Brittleness index in brittleness prediction, we compare it with other conventional Brittleness indexes in aspects of brittleness sensitivity and physical response. The results show that the ability to characterize the mineral’s brittleness of new brittleness indexes is much stronger than the ability of conventional brittleness indexes. And the analysis about cross-plot colour-coded by the new Brittleness index could support the favoriable informations for elastic property and brittle characteristics in “sweet spot” zone of tight sandstone oil reservoir. In theory, the above characteristics of new brittleness index are more conductive to brittleness evaluation for tight sandstone oil reservoir.
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Crustal Structure of the Galicia Continental Margin (NW Spain) from Gravity Data Analysis and Modelling
Authors M. Druet, A. Muñoz-Martín and A. CarbóBetween 2001 and 2008, new marine gravity data have been collected over the North Atlantic Ocean rounding Galicia margin (NW Spain). We present a gravity data analysis and a N-S density model, focused on the interpretation of the crustal structure of the margin. For that purpose, a Complete Bouguer Anomaly grid has been calculated. This grid has been filtered in the frequency domain (both low-pass and band-pass filtering) to generate, respectively, a long-wavelength Bouguer Anomaly map (related to lithospheric mantle sources) and a mid-wavelength Bouguer Anomaly map (related to crustal density variations). Additionally, a N-S density model across this area has been performed. The analysis of these new data reveals the presence of compressive tectonics on this margin, particularly to the North, that generates crustal shortening and uplift of the seamounts area. During the Cenozoic compressive stage, besides the inversion of previous normal and strike-slip faults, new compressive structures are generated in the northern edge of the seamounts area, leading to the thickening of oceanic crust by means of a crustal-scale great fold and thrust, which is the westward continuation of those structures observed on the North Iberia compressive margin.
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3D Envelope Inversion
More LessThe envelope of the wavefields carries ultra low frequency information which can be used to recover the large-scale component of the model, and the initial model dependence of full waveform inversion can be reduced. We extended the envelope inversion method to 3D and used GPU clusters for the implementation, Numerical tests using the resampled 3D Overthrust model proved the validity and feasibility of the proposed approach. The inverted velocity from the combined (EI+WI) envelope inversion plus waveform inversion indicated that it can deliver much improved result compared with regular full waveform inversion.
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Laplace-domain Waveform Inversion for the 3D Acoustic-elastic Coupled Media
More LessIn the marine streamer survey, the sources and receivers are located in the homogeneous acoustic media; however, the media below the sea bottom, which is the target area, has highly heterogeneous 3D elastic properties. Thus, the hydrophone pressure data contain various elastic effects, such as shear wave effects, mode converted waves and amplitude offset variation, and these effects impact the Laplace-transformed wavefield. Therefore, it is not possible to perfectly reduce the misfit between modelled and observed data using only acoustic wave equations. In this study, we developed a Laplace-domain waveform inversion algorithm for 3D acoustic-elastic coupled media. We can precisely simulate the environment of a conventional streamer marine survey by coupling the 3D acoustic and elastic wave equations using a proper boundary condition at the solid-fluid interface. Also, for the matrix solver, we suggest using the parallel sparse direct solver library, which was developed by the MUltifrontal Massively Parallel Solver (MUMPS) team. Because this is a direct matrix solver, we do net lose the main advantage of implicit modeling (e.g., frequency or Laplace domain modeling) over the explicit time-domain modelling when we solve the wave field for a number of shots.
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Seismic Imaging of Two-layer Deformation Lithosphere in the Indian Ocean
More LessWe obtain a very deep seismic image from the offshore northern Sumatra that shows faults down to 45 km depth by boosting low frequency signal during data processing, which is much better than the traditional processed result. The amplitude of these deep reflectors in the mantle decreases linearly with depth down to 25 km and then remains constant down to 45 km. We also find that the number of faults, the number of earthquakes and the cumulative moment released as a function of depth show a similar pattern, suggesting that the lithospheric mantle deformation in this region can be divided into two layers: a highly fractured serpentinized upper layer and a pristine brittle lithospheric mantle where great earthquakes initiate and large stress drop occurs. It is also consistent with the depth of second layer of double Benioff zone in most of the subduction zones.
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Plane-wave Least-square Reverse Time Migration with Source Polarity Encoding
Authors C. Li, J.P. Huang, Z.C. Li, R.R. Wang and M. YuanPlane-wave least-square reverse time migration (PLSRTM) delivers high quality images but costs less computation compared with conventional least-square reverse time migration. However, a number of plane-waves are necessary for crosstalk suppression. The paper introduces source polarity encoding to the plane-waves to reach better suppression to crosstalk. Combined with randomized sampling approach, the computation cost of PLSRTM can be decreased a lot. Numerical tests on SEG rugged topography model verifies that the combination with source polarity encoding and randomized sampling can obviously improve the imaging result and computation cost of PLSRTM.
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A New Approach to Reservoir Modeling and Simulation Using Boundary Representation, Adaptive Unstructured Meshes and the Discontinuous Overlapping Control Volume Finite Element Method
Authors P. Salinas, J.R. Percival, D. Pavlidis, Z. Xie, J. Gomes, C.C. Pain and M.D. JacksonWe present a new, high-order, control-volume-finite-element (CVFE) method with discontinuous Nth-order representation for pressure and (N+1)th-order for velocity. The method conserves mass and ensures that the extended Darcy equations for multi-phase flow are exactly enforced, but does not require the use of control volumes (CVs) that span domain boundaries. We demonstrate that the approach, amongst other features, accurately preserves sharp saturation changes associated with high aspect ratio geologic features such as fractures and mudstones, allowing efficient simulation of flow in highly heterogeneous models. Moreover, in conjunction with dynamic mesh optimization, in which the mesh adapts in space and time to key solution fields such as pressure, velocity or saturation whilst honoring a surface-based representation of the underlying geologic heterogeneity, accurate solutions are obtained at significantly lower computational cost than an equivalent fine, fixed mesh and conventional CVFE methods. The work presented is significant for two reasons. First, it resolves a long- standing problem associated with the use of classical CVFE methods to model flow in highly heterogeneous porous media; second, it reduces computational cost/increases solution accuracy through the use of dynamic mesh optimization without compromising parallelization.
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3D Modeling of the CoalBed Methane (CBM) Resources in the Taldykuduk Block Karaganda Coal Basin, Kazakhstan
Authors J.J. Royer, R. Sadykov, I. Panfilova and E.K. OgayCoal Bed Methane (CBM) is gas stored in coal layers, generally extracted from wells after hydraulic fracturing and/or CO2 or solvent injections. The Karaganda Basin was selected to develop CBM production because of its huge gas potential (4 300 Bm3 equivalent to 2 billion tons of coal, with gas content about 15-25 m3/t of coal (for comparison San Juan basin, US, has < 20 m3/t)). This work aims at modeling the Taldykuduk block coal layers focusing on CBM production. The methane extracted during mining actually released in the atmosphere, will be collected. A 3D geological model was built on Gocad/Skua using all available datasets (about 1000 wells over 84 km2, cross-section and maps acquired during coal exploitation, and fractures network reported on geological cross sections). The resulting 3D model including hundreds of faults, is used to simulate the secondary recovery of methane by CO2 injection on a flow simulator, assuming a two phase dimensionless formulation in a double porosity model with the matrix (m) and the fracture (f) for which the initial and boundary conditions are different. The resulting 3D models had helped in better understanding the regional tectonic structures, faults relationships, the hydrogeology regime and the potential gas reserves.
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Performance of Water Injection Wells - Chestnut Field
Authors M. Langford and J. TovarWater injectors are critical to the long-term success and reserves recovery of hydrocarbons production and reservoir management. Injectors are also critical to the pressure support of the reservoir that allows production and mechanical integrity of the rock. Lack of injection does, in many cases, lead to impaired production and changes in petro-physical properties at the wellbore and deep into the reservoir. Limited references are found in the literature in terms of design and performance management of water injectors. Our work describes in detail the design and performance processes for two (2) injection wells (wells 12 & 17) in the Chestnut field, located in block 22/2a in the UKCS of the North Sea. Producing from a shallow sandstone reservoir, the field is exploited using two (2) producers and two (2) injectors. All wells are subsea and an active sand and pore pressure management program has been in place for 6 years. The design rationale and parameters are presented and the results obtained discussed. Well performance is then analysed in terms of pressure support, injectivity and operational problems that lead to injectivity impairment and one well failure. The methodology for evaluation of reservoir performance is described; comparison between the typical analytical tools such as the Hall or the Impedance Methods is discussed including the results obtained. A performance comparison based on real-time data from the wells, to identify and predict events such as injectivity impairment, the need for intervention or remedial action, is presented.
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An Alternative Hydrocarbon Indicator Based on Rock Physics Template
More LessReservoir fluid discrimination is an indispensable part of seismic exploration. Reliable fluid discrimination helps to decrease the risk of exploration and increase the success rate of drilling. Based on the H-M contact theory, a rock physics template was built in the domain of the crossplot of compressional modulus and ratio of compressional modulus and shear modulus. An alternative hydrocarbon indicator RPTI (rock physics template indicator) was proposed according the fluid trend in this rock physics template. This combined hydrocarbon indicator not only solves the problem easily caused by single indicator in discrimination, but also reduces the influences of human factors. A corresponding alternative elastic impedance inversion method was proposed based on the Bayesian theory to improve the accuracy of inversion results. The profile of this indicator is an intuitionistic interpretation of fluid contents. Real data tests demonstrate the applicability and validity.
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Ray-tracing-based Input Data Selection RTM - A Target Oriented Approach for Clearer Subsalt Image
Authors C. Peng Inc, W. Gou Inc and G. Liu Inc IncWe present an input data-selection workflow based on 3D ray-tracing to improve the reverse time migration image in areas of poor illumination and low signal-to-noise ratio. It is effective for imaging subsalt three-way closure with weak subsalt primaries and strong noise levels. The workflow can be applied to any type of survey, but it is most suitable for full azimuth geometries. We focused on data selection using 3D ray-tracing, but this workflow can be easily adapted to use finite-difference wave-equation modelling. The data selection information can either be used to scale up weak primary signal before migration or to be migrated separately and merged into a full migration result in the post-migration stage.
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Accurate Seismic Wavefield Simulation in 3D Heterogeneous Media - A Massively Parallel Algorithm
Authors M.K. Sen, P.L. Stoffa and R. Seifty, anisotropy, viscosity and poro-elasticity are now becoming increasingly more important for analysis of multi-azimuth and rich azimuth data. Here we present an algorithm for solving anisotropic wave equation in 3D in which spatial derivatives are computed in Fourier domain while time updates are computed using the rapid expansion method. Although the use of the pseudo-spectral method together with REM ensures a desired level of accuracy, the algorithm is memory and CPU intensive. To address this, we have developed several parallelization strategies – one such approach involves computing wavefields in different parallel banks and uses parallel FFTs ensuring minimal communication overhead. The algorithm can handle arbitrary anisotropy including monoclinic media. We will present several examples for models with varying degree of complexity and anisotropy. The algorithm can easily be extended to perform reverse time migration in elastic media.
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Differential Kuster-Toksöz Rock Physics Model for Multiple-porosity Rocks
More LessKuster-Toksöz model (KTM) is a classical rock physics model concerning the influence of pore geometry on elastic wave velocities. However, this model is limited to dilute concentration of pores. That is to say, the porosity could not be too high (porosity (Φ)/aspect ratio (α) <<1). In order to solve this problem, this paper transforms the Kuster-Toksöz model into a differential Kuster-Toksöz treatment. In other words, we consider a process whereby porosity, or equivalently inclusions with certain geometries, increases step by step from zero up to its final value. Obviously, this new differential Kuster-Toksöz model (DKTM) is superior to the classical KTM and DEM (short for differential effective medium) model since it considers multiple–porosity and higher porosity rocks. Furthermore, when void pores and clay are considered as inclusions, we analyze the elastic moduli simulated by KTM and DKTM, the geometry parameter of which is described by Berryman’s special pores. The result shows that, DKTM is superior to KTM for obtaining satisfactory elastic properties under high porosity and high volume fraction inclusion condition.
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