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76th EAGE Conference and Exhibition 2014
- Conference date: June 16-19, 2014
- Location: Amsterdam, Netherlands
- Published: 16 June 2014
151 - 200 of 1028 results
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Prestack Exploding Reflector Modeling and Migration in TI Media
Authors H. Wang and T. AlkhalifahSummaryPrestack depth migration in anisotropic media, especially those that exhibit tilt, can be costly using reverse time migration (RTM). We present two-way spectral extrapolation of prestack exploding reflector modeling and migration (PERM) in acoustic transversely isotropic (TI) media. We construct systematic ways to evaluate phase angles and phase velocities in dip oriented TI (DTI), vertical TI (VTI) and tilted TI (TTI) media. Migration results from the Marmousi VTI model and the BP2007 TTI model show the feasibility of our approach.
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Fresnel Beam Migration in Anisotropic Media
More LessSummaryIn order to overcome the shortcomings of conventional Kirchhoff prestack depth migration (PSDM) and Gaussian beam migration (GBM), a new Fresnel beam migration (FBM) method is proposed by introducing the traveltime field produced by dynamic programming approach in anisotropic media. The beam width (Fresnel zone) of our method has a more definite physical meaning than GBM, which achieve the higher accuracy because the traveltime calculation method has no limitation on large velocity contrast. The major steps of FBM are traveltime computation, the central ray trajectory tracing, Fresnel zone calculation and wavefield back-propagation. The proposed method resolves spatial ambiguities caused by elliptical traveltime isochrones summation with limited aperture, and it is an economic way to generate angle gathers for velocity model building. The numerical examples demonstrate the accuracy and effectiveness of this method.
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Amplitude-friendly Angle Migration with Stabilized Q
Authors S.-K. Foss, D. Merten, N. Ettrich, E.S. Karlsen and J. MispelSummaryAmplitude-friendly imaging in complex media may also require accounting for attenuation described by a spatially varying Q-model. Here, we extend the ray-based angle migration to account for Q. Any migration with attenuation compensation needs to handle the inherent signal-to-noise ratio of the data or it may boost noise. We present both the use of a stabilization of the effect of Q in the migration and a data-driven reflection enhancement by weighting the summation in the migration to specular events. Both are important in controlling the noise.
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Fast and Accurate Solutions of the Eikonal and Transport Equations
Authors M. Noack and S.R. ClarkSummaryA method is proposed to solve for travel times and amplitudes simultaneously. A new stencil shape offers the possibility for an abundant parallelization. Transport and travel time fields can be used to estimate the Helmholtz equation. The main objective is to obtain the Helmholtz Green’s function as fast as possible.
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Multiple Imaging Based on Stereographic Imaging Condition
More LessSummaryThe multiples usually have wider illumination range and contain more information than the primary reflection, so instead of suppression, multiple imaging has attracted more and more attention nowadays. The traditional multiple imaging methods replace the source wavelet with recorded data and use the predicted multiples as the receiver record, however, the crosscorrelation of the unrelated events will introduce heavy crosstalk artifacts when using the conventional imaging condition which the primary migration methods used. In this paper, we propose to introduce the stereographic imaging condition to solve this problem, by adding a local slope constrain, this method can well suppress the crosstalk artifacts. In order to improve the computational efficiency, we adopt the one-way wave-equation migration method for multiple imaging in this paper. The numerical examples verify the feasibility and effectiveness of this method, better multiple imaging results are obtained in the numerical tests.
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Omnidirectional Extension of Full Wavefield Migration
Authors M. Davydenko, D.J. Verschuur and A.J. BerkhoutSummaryFull wavefield migration (FWM) is an iterative inversion-based imaging technique that aims at explaining the complete measured data by the modeled data. The predicted data is computed using the modeling scheme in which all the scattering, including the transmission effects and all kinds of multiples, is generated due to the estimated reflectivity from the previous iteration. However, since the one-way extrapolation is used, the current method is limited in the angles of propagation. In this paper we extend the FWM by applying the wavefield modeling and imaging in the orthogonal direction as well. We show two examples, where the propagation is improved. Furthermore, diving waves and multiples related to them can now be handled.
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Nonlinear Sensitivity Operator and Its De Wolf Approximation in T-matrix Formalism
Authors R.S. Wu, C. Hu and M. JakobsenSummaryWe derived the Nonlinear sensitivity operator in nonlinear tomographic waveform inversion based on the theory of nonlinear partial derivative operator. We apply the renormalization procedure (De Wolf approximation) to the forward and inverse T-matrix series. Numerical tests proved that the renormalized inverse scattering series has much better convergence property than the inverse Born series. This convergence improvement may be applied to the iterative procedure of waveform inversion.
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Deabsorption PSTM Method and Application in Daqing Oilfield
By W.C. WangSummaryAccording to daqing oil field seismic data high resolution processing requirement, we have developed a migration scheme that can compensate absorption and dispersion caused by intrinsic attenuation in subsurface media. The scheme was developed by adapting prestack time migration (PSTM) in the frequency domain. Instead of applying a commonly used Q factor, we devised an effective Q parameter to compensate absorption and dispersion. The effective Q determines the frequency dependent traveltime and amplitude at one imaging location by only one value. As a result, the effective Q can be estimated by scanning technology. The proposed scheme can determine an effective Q model using surface seismic data during migration. Stabilization is achieved by introducing a smooth, maximum-limited gain function that matches the exact amplitude compensation factor when it is less than the user-specified gain limit. Higher-resolution imaging results of Daqing oilfield seismic data are obtained by application of the method.
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Rotation Parameters for Model Building and Stable Parameter Inversion in Orthorhombic Media
Authors C.M. Lapilli and P.J. FowlerSummarySymmetry groups commonly used to describe seismic anisotropy include transverse isotropy, orthorhombic, monoclinic, and triclinic. For all but the last, the choice of particular orientations of the coordinate system can substantially simplify parameterization of the anisotropy. Choosing a coordinate system requires defining a rotation in three-dimensional space relative to fixed world coordinates. We discuss here two major families of rotation parameterizations: Euler angles and axis/angle quaternion representations. Either method can work well for forward modeling. However, for traveltime tomography or full-waveform inversion, the inverse problem formulated in Euler angles can become ill-posed because very different choices of angle parameters can yield nearly identical data. In the worst case, there can be a complete loss of a degree of freedom, making it difficult to invert for important model parameters such as fracture orientation. Quaternions provide an alternative representation for 3D rotations that avoid these inversion problems. Quaternions also provide efficient and well-behaved interpolation of rotation angles, as well as differentials of data with respect to rotation parameters.
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Orthorhombic Extension to HTI Velocity Analysis -Theory and Application to a High Density Aquisition
Authors C.M. Davison, M.J. Grimshaw, E.M. Murray, M. Kowalczyk-Kedzierska, S. Angio and A. OurabahSummaryAzimuthal velocity models are now widely used for land seismic exploration. In particular, Horizontal Transverse Isotropy (HTI) models have often been applied as the anisotropic velocity model of choice, to extract velocity information from situations where the earth consists of horizontally fractured media. The velocities extracted can be used both to perform azimuthally dependent move-out to flatten the CMP gathers, providing a sharper and clearer stack, and also to generate the interval velocity models via generalized Dix inversion, which are a powerful tool for interpreters when dealing with fractured earth models. However, HTI velocity models are known to be insufficient as a modelling tool in certain circumstances, particularly in surveys where large offsets are present, resulting in incidence angles of over 30 degrees where higher order terms in the move-out equation start to become significant. This study therefore implements an orthorhombic velocity model as an extension to the standard HTI model, where azimuthally dependent higher order move-out is present in the move-out equation. The method of solution of the orthorhombic model is described, together with an application to a Full-Azimuth high density Independent Simultaneous Shooting (ISS®) survey as an illustration.
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Anisotropy Estimation and Image Remapping Using Model Based Moveout
Authors Z. Liu, N.D. Whitmore and C. ZhouSummaryTypically model parameter estimation is achieved through multiple iterations of linearized tomography and depth migration. In this paper we discuss a method to reduce the migration effort by applying local approximations to the imaging and modelling operators using a model based moveout, which is a mapping between imaged specular reflections in initial and updated models. This allows for very efficient imaging and model testing, so that multiple iterations of imaging and linearized tomography or generalized iterative inversion can be applied. The model based moveout and tomography is demonstrated for anisotropic inversion in the case of known subsurface control, where the vertical velocity is known and the task is to estimate the anisotropic Thomsen parameters for VTI media. The method requires an iterative joint inversion of these parameters by projecting residual depth errors onto model updates.
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A Quartic Traveltime Inversion Method for TTI Media and Applications on Anisotropic Migration and Fracture Prediction
More LessSummaryCurrently, NMOz (Normal Moveout Versus Azimuth) plays an important role in anisotropy-related processing. It can also provide parameters required for both anisotropic migration and kinematic fracture prediction. However, NMOz algorithm is developed on the basis of the traveltime formula with a presumed hyperbolic moveout, which losses considerate accuracy due to the truncation of quartic moveout and thereby usually fails to describe kinematic behaviors at large offsets. In this paper, we present a concise and more accurate traveltime formula for TTI media (with a horizontal reflector) by incorporating quartic moveout, which is proven to be in better agreement with most routine VTI or HTI approximations. In practice, we apply the new traveltime formula into a fractured physical model and a carbonate reservoir. Results show that events of common-offset azimuthal CRP gather from anisotropic migration becomes more flattened and the reflection energy is also remarkably concentrated even for large offsets. Besides, predicted fracture intensity and strike both show a close tie to tectonic movements, which may helps a better understanding of fracture evolutions.
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Detecting and Estimating Anisotropy Errors Using Full Waveform Inversion and Ray-based Tomography
More LessSummaryFull waveform inversion (FWI) is widely used to obtain high-resolution subsurface parameters using diving and refracted waves in a wide range of acquisition scenarios. Frequently, however, quality checks in the image domain using conventional Pre-Stack Depth Migration (PSDM) indicate that the curvature of the common image point (CIP) gathers does not systematically improve compared to ray-based reflection tomography (RAY) counterparts.
We investigate the drivers for the inconsistency between the two approaches. The transmission-based FWI scheme relies heavily on wide angle arrivals, while reflection tomography relies on the near angle reflections due to impedance contrasts. Therefore, these two approaches provide complementary information of the Earth, and we try to exploit this view to evaluate the anisotropy parameters and obtain better estimates of and V_0, assuming knowledge of δ. We present the challenges of decoupling these parameters using a canonical example. We also propose a heuristic approach to estimate the anisotropy and velocity errors to simultaneously minimize the cost functions of FWI and RAY. We apply the workflow to the Marmousi data set and demonstrate that we can, to some extent, recover long wave components of the anisotropy. A field data example will be shown in the presentation itself.
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The Characteristic Wave Decomposition and Imaging in VTI Media
More LessSummaryA characteristic wave decomposition (CWD) method is presented in this paper, which can express the seismic data sparsely. We perform CWD by double beam forming for a compressed seismic wave-field and its index. Based on the beam-formed wave-field in characteristic domain, a beam-based characteristic wave imaging method (CWI) is put forward. Due to the flexibility and efficiency to generate angle gathers for velocity model building, the CWI is a useful alternative to Kirchhoff and wave-equation migrations. Extension of CWI to anisotropic media by introducing ray tracing system in transverse isotropic with a vertical symmetry (VTI) media achieve a better imaging result. The CWI has a theoretical speedup of 1∼2 orders of magnitude over the conventional Kirchhoff migration methods. Besides, it can handle low signal to noise ratio data and target oriented imaging conveniently, and angle gathers can be produced naturally by CWI. Consequently, the CWI is an efficient technique for large scale seismic imaging and 3D velocity model building.
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3-D Waveform Tomography Sensitivity Kernels for Anisotropic Media
Authors R. Djebbi and T. AlkhalifahSummaryThe complications in anisotropic multi-parameter inversion lie in the trade-off between the different anisotropy parameters. We compute the tomographic waveform sensitivity kernels for a VTI acoustic medium perturbation as a tool to investigate this ambiguity between the different parameters. We use dynamic ray tracing to efficiently handle the expensive computational cost for 3-D anisotropic models. Ray tracing provides also the ray direction information necessary for conditioning the sensitivity kernels to handle anisotropy. The NMO velocity and η parameter kernels showed a maximum sensitivity for diving waves which results in a relevant choice of those parameters in wave equation tomography. The δ parameter kernel showed zero sensitivity; therefore it can serve as a secondary parameter to fit the amplitude in the acoustic anisotropic inversion. Considering the limited penetration depth of diving waves, migration velocity analysis based kernels are introduced to fix the depth ambiguity with reflections and compute sensitivity maps in the deeper parts of the model.
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Automated Travel Time Tomography Using Early-arrival Gaussian Packets
Authors J. Tang, A. Lau, M. Woodward, C. Peng and A. GonzalezSummaryWe present a newly developed method of velocity inversion that does not require explicit picking of either common image gathers or first breaks. Seismic data are first decomposed into Gaussian packets. The early-arrival packets are selected and used as input for an anisotropic traveltime tomography solver. Using information contained in the packets, we can correctly model head waves, and diving waves. The workflow is fully automated and can be used for in a batch processing environment with minimum human intervention. We demonstrate the method with two synthetic examples and one real-data example. In the synthetic examples, we are able to use super-long offset data and reduce traveltime residuals from 400ms to 5ms or less in three iterations. In the real-data example, we achieved an accurate velocity model that yields both an improved image and flatter common-image gathers. This method can also be combined with traditional post-migration tomography.
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Mapping Basement and Moho along Brazil’s Equatorial Margin Using Potential Field Data to Assist Petroleum Exploration
Authors S.L. Markham, I. Kivior, P. de Lugao, J. Button, S. Beavers, T. Wise and S. SenderowitzSummaryLow resolution regional magnetic and satellite gravity datasets were used to conduct an interpretation of the crustal structure along the Equatorial Margin of Brazil. Unique potential field interpretation techniques were used to map basement with a resolution of 10×10km and Moho with a resolution of approx. 30×30km. The crustal structure, including major faults, troughs and crustal highs were mapped along the 2000km long Equatorial Margin. The depth to basement derived from the potential field data shows good correspondence to the available well and seismic data.
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3D Regional Velocity Modeling
By C. MagneronSummaryBuilding a realistic and accurate regional velocity model at the scale of a basin is only possible by integrating seismic velocity data. Traditionally the integration of the seismic velocity data into a velocity model is made by a layer cake approach. This is a quite incomplete integration as the approach stacks, layer by layer, the vertical structuration of the seismic velocity data. At the scale of a basin, a fully 3D integration of the seismic velocity data sets, coupled with previous qualification and merge steps, leads to the generation of a 3D continuous velocity model. That fully 3D approach, possible thanks to advanced geostatistical techniques, has been applied on several basins. The observed depth uncertainty attached to the velocity models is on average about +/−70m (error far from the wells, expressed in terms of 2 × standard deviation of the errors distribution).
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The Taymyr Fold Belt - An Emergent Frontier of Petroleum Exploration?
Authors K. Sobornov, A. Afanasenkov and D. YakovlevSummaryThe Taymir fold belt lies between the Arctic Ocean and Siberian platform covering area of about 0.4 mln. km2. Until recently the area has been one of the few untouched exploration frontiers left in Russia.
Geological model of the area was constrained by scarce regional dataset with surface mapping being the most informative source of data. New seismic and magneto-telluric (MT) surveying conducted in the south-western part of the fold belt provided an important insight into its subsurface structure. The fold belt includes thick- and thin-skinned thrusts involving basement and Vendian-Mesozoic sedimentary cover producing a system of south-vergent thrust sheets sealed by transgressive Jurassic-Cretaceous deposits. A belt of diapirs formed by Lower Paleozoic (Upper Ordovician?) salt are recognized in the central part of the fold belt. A new petroleum play concept is developed based on the new data. It includes a variety of diverse including - thrust –related 4-dips, positive flower structures, carbonate build-ups, zones of pinching-out and truncations, traps associated with salt diapirs.
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Complexity of Sandstone Bodies in the Northern North Sea and Their Implications on Hydrocarbon Prospectivity
Authors O. Olobayo, M. Huuse and C.A.L. JacksonSummaryMillions of barrels of hydrocarbon are produced daily from sandstone reservoir intervals in deep-water settings from petroliferous basins such as the North Sea, Niger Delta etc. These sandstones are commonly believed to have been deposited by gravity-flow processes inform of large, deep-water channel-lobe systems and low-stand fans; however, detailed investigation reveals unusual geometries that are difficult to unravel by normal depositional processes. It is believed that, the sandstones have been subject to subsurface remobilization and injection that significantly modified their geometries. Early Tertiary sandstones in the South Viking Graben, Outer Moray Firth and East Shetland Platform in the North Sea (Alba, Balder, Chestnut, Kraken, Mariner, Volund etc) show evidence of such modifications from seismic, wireline logs and core data ( Lonergan et al. 2000 ). Products of these post-depositional processes are recognized from the Cretaceous to Pliocene intervals in the study area. They include remobilized sands, sand injectites and sand extradites embedded in mud-rich successions. Evidences show the Cenozoic Northern North Sea underwent basin-scale remobilization and injection in a scale that has not been previous documented in the North Sea or any other basin in the world. We observe an exclusive stratigraphic overlay of these unconventional sandstones and if the sands are connected; could have impacted hydrocarbon prospectivity in the basin. Therefore, there is need to incorporate them into the current Cenozoic stratigraphic framework and geologic models at the early stages of exploration; to ascertain to what degree they may have influenced fluid flow in the basin. We propose a multiple phase emplacement through the interval.
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Late Jurassic Rifting in the Southern Central Graben - A Complex Story Simplified
SummaryIn order to be able to predict the distribution of reservoir sands and of grainsize and porosity trends in a hydrocarbon province, it is essential to understand the basin evolution in detail. In this study, an attempt is made to reconstruct the complex basin evolution of the southern Central Graben area by careful correlation of sedimentary successions from the different structural elements. The Late Jurassic rift phase is complex: a change in tectonic regime occurs, subsidence varies dramatically through time and space and former depocenters may become sources for erosion. In this paper a break down is proposed for the basin evolution in three discrete steps, each of which is closely related to changes in the tectonic regime. The basin fill of the southern Central Graben area is displayed in Wheeler type of diagrams, showing the facies relationships between the various parts of the basin.
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Structural Evolution and Its Implication to Heavy Oil Potential in Iliran High, South Sumatera Basin, Western Indonesia
Authors Z. Holis, D.A. Firmansyah, W. Romodhon, M.K. Kamaludin and S. DamayantiSummaryHeavy oil resource is one of the significant hydrocarbon potential in Sumatra. The study area of Iliran High occupied in the eastern flank of the South Sumatera Basin. South Sumatra Basin was formed as pull-apart basin related to NW-SE trending dextral strike-slip faults. The objective of this research is to analyze structural evolution and to explain its implication to the heavy oil accumulation in Iliran High area, South Sumatra Basin.
The methods used in this study included well correlation, petrophysical analysis, 2D and 3D seismic interpretation, and palinspatic reconstruction. Palinspatic reconstruction or retro deformable cross-section in this study was conducted using balancing cross-section techniques.
Interaction rifting and strike-slip has occurred during Paleogene controlling the syn-rift deposition as hydrocarbon source for Iliran High structure. Strike-slip deformation is continuous to Pliocene-Pleistocene where mode of rifting changes causing reversal structural style. Pliocene-Pleistocene deformation caused Iliran High structure become the highest point and responsible of reservoir to become very shallow and some part exposed. Uplifted Iliran High increasingly caused a part of reservoir, trap, and seal were eroded so that “early light oil accumulation” preservation is disturbed. This disturbed preservation caused variation of biodegradation so that “early light oil accumulation” becomes heavy oil.
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The Geological Structure of the Netherlands Continental Shelf - Results of a Detailed Mapping Project
Authors J.H. ten Veen, J.C. Doornenbal, M. den Bulk, S.F. van Gessel and N. WitmansSummaryIn 2011, TNO-GDN concluded a 5 year geological mapping of the Netherlands Continental Shelf. In this project all public data from hydrocarbon exploration were used resulting in a major update of the dataset and a variety of deliverables available at www.NLOG.NL. The stratigraphy of more than 400 wells has been re-examined and amended where necessary. 2D and 3D seismic surveys were re-interpreted and new velocity models were used for time-depth conversion of the interpretations. This resulted in a structural model from base Zechstein to base Neogene. Also 30 reservoir intervals were added to the model. For the offshore area around 3800 faults were interpreted. The offshore faults where the first to be stored in a spatial fault database. Apart from detailed spatial information, all faults are also labelled with fault-kinematic-, geomechanic- and dimensional properties. This database will soon become publicly available. The uncertainty related to interpretation and data-processing has been evaluated. This resulted in maps showing the standard deviation for the depth of the main stratigraphic intervals. Based on these new subsurface mapping results a new unambiguous- and data-driven classification of structural elements is proposed that reflects the coupling between the different stratigraphic superpositions encountered and the complex tectonic evolution.
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Multi-scale Modelling Stromatolite Deposits with a Kernel Learning Approach
Authors V. Demyanov, P.W.M. Corbett and M. SaadSummaryThe paper proposes a novel approach for modelling multi-scale pattern of stromatolite deposit geometry. Spatial modelling of microbial carbonates is challenging due to the multi-scale structure of their porosity and permeability patterns. Conventional geostatistical methods are limited by stationarity assumptions, while object based approach may result in over-complicated representation of trends and bio-diversity. Therefore, it becomes difficult to adequately represent uncertainty across possible spatial patterns.
The proposed kernel learning method is a data driven non-linear predictor that is based on blending spatial features derived from an outcrop analogue. Multiple kernel learning algorithm is capable to learn the relevant features from data and propagate them into prediction. Uncertainty of the predicted pattern is reflected by variation in the impact of individual input features. Application of the algorithm is demonstrated using a outcrop stromatolite analogue from Brazil.
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3D Micro- & Macro- Characterization Workflow for Carbonate Reservoirs
Authors M.F. Leon Carrera, N. Rodriguez Morillas and L. FontanelliSummaryThe field development of carbonate fields arise a high complexity due to the heterogeneity of the rock. The characterization and modelling of carbonates involve the understanding of sedimentation and diagenetic processes. The workflow in reservoir characterization integrates several data types at different scales (i.e. seismic, well data, sedimentological models, analogous models, etc.) with the aim to generate 3D static and dynamic models that attempt to predict the reservoir behaviour In the last decade, the industry has developed methods for characterizing carbonate rocks at microscopic scale using confocal microscopy, Micro- /Nano- X-ray Computed Tomography (CT) or at macroscopic scales using CT-Scan technology. These methodologies allow studying digital data and analysing the distribution of the pore network in three dimensions, in order to determine petrophysical properties. Great emphasis has been placed on these techniques to determine the storage capability and flow of rock cores. However, it is needless to say that such capabilities are affected by components constituting the rock and that the distribution of the components affects the petrophysical properties. We show a methodology for the characterization of carbonate rocks at micro and/or macro scale, inspired by the characterization modelling workflow of reservoirs. Using the techniques developed for digital rocks, we analysed the spatial organization of the components that contribute to the pore network. In this way, we selected the representative samples of each facies and we discretized each main component. This is called “facies model” at high scale resolution. The petrophysical properties like porosity and permeability were modelled using Geostatistical methods as a function of the components that impact the flow. Once the 3D static model was built for each sample, we proceeded with the flow simulation for calibration and validation with laboratory data. Finally, we propagated the samples to core scale using Geostatistical methods. This methodology allowed a better understanding of carbonate rock property distribution at core that later on can be extrapolated to the field later on. The methodology was applied to confidential data of a Repsol asset therefore generic terms are used from now on.
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Simulation of Carbonate Dissolution at the Porescale Using a Streamline Method
Authors J.P. Pereira Nunes, A.Q. Raeini, B. Bijeljic and M.J. BluntSummaryCarbon dioxide is currently being injected into saline aquifers and depleted oil and gas reservoirs with both enhanced oil recovery (EOR) and carbon capture and storage (CCS) purposes. The injected CO2 in contact with the reservoir fluids creates an acidic mixture that can potentially react with the host rock causing changes in the petrophysical properties of the reservoir. From the experimental point of view much work has been recently published in the scientific literature about the impact of acidic brine in carbonate reservoirs. These laboratory results indicate that strong rock-fluid interactions may occur, however, pore-scale models capable of predicting how the petrophysical changes associated with these reactions can be related to transport properties are yet to be developed. The recent increase in computational power and tomographic capability made possible the acquisition of high resolution images of heterogeneous carbonates that are very suitable to study in detail the flow and transport properties of such rocks. In this paper we demonstrate how micro-CT images of carbonate rocks can be used to model reactive transport at the pore scale. We apply a particle tracking algorithm based on a pore-scale streamline tracing method to simulate carbonate dissolution.
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Dynamic Pore-scale Imaging of Reactive Transport in Heterogeneous Carbonates at Reservior Conditions
Authors H.P. Menke, B. Bijeljic, M.G. Andrew and M. BluntSummaryFour carbonate rock types were studied, two relatively homogeneous carbonates, Ketton and Mt. Gambier, and two very heterogeneous carbonates, Estalliades and Portland Basebed. Each rock type was imaged using dynamic x-ray microtomography under the same reservoir and flow conditions to gain insight into the impact of heterogeneity. A 4-mm carbonate core was injected with CO2-saturated brine at 10 MPa and 50oC for 2 hours. Depending on sample heterogeneity and X-ray source, tomographic images were taken at between 30-second and 20-minute time-resolutions and a 4-micron spatial resolution during injection. Changes in porosity, permeability, and structure were obtained and a pore-throat network was extracted. Furthermore, pore-scale flow modelling was performed directly on the binarized image and used to track velocity distributions as the pore network evolved.
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Carbonate Coquina Reservoirs - New Insights for Petrophysical Reservoir Characterisation
Authors R. Camara, P. Corbett, C. Tavares, A. Machado, E. Jesus and L. BorghiSummaryWith the recent discoveries of Pre-Salt oil fields in lacustrine carbonate reservoirs of Barremian-Aptian age, on both African and Brazilian Margins of the South Atlantic, interest has increased in the petrophysical aspects of these complex reservoirs. Some of these reservoirs are composed of coquinas which are limestones composed of shells or shell fragments, in this case bivalves. The petrophysical challenges in coquina pore systems result from wide range of textures, fabrics and diagenetic processes showing;
- Primary shells preserved in fine-grained carbonate and/or mixed carbonate-clastic matrix
- Dissolved or partially dissolved and corroded shells in a fine-grained matrix
- Recrystallised shells and matrix
- Dissolution of fine-grained matrix and preferential preservation of shells
- Gradations between, and combinations of, all of the above
We have investigated methods to quantify porosity, measure geometry, scale and distribution of pore space and its connectivity in plugs from coquina samples from the Sergipe-Alagoas Basin (onshore NE Brazil). These are the results of our initial investigation, where we could relate m to the type of porosity, connectivity of pores, pore throat size distribution and permeability. In general, the increase of porosity in these samples correlates with an increase in m.
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A New Algorithm of Modified Fuzzy C Means Clustering (FCM) and the Prediction of Carbonate Fluid
More LessSummaryAimed at the disadvantages of Fuzzy C Means Clustering (FCM) algorithm which is sensitive to initial values and easily falls into local convergence, a new FCM algorithm named as CQPSO-FCM is proposed in this paper, which makes a combination of FCM algorithm and Chaotic Quantum Particle Swarm Optimization (CQPSO) algorithm. In order to solve the problems mentioned above and improve the ability of fuzzy classification, CQPSO algorithm is used to initialize the membership matrix, which significantly improves the global optimum search ability of the proposed algorithm. What’s more, this method could be used to predict accurately the fluid of complex fracture-cavity carbonate reservoir. Because the common fluid director of AVO inversion would not be available enough in fluid identification of carbonate reservoir, this method is then employed to establish a relation of fluid and reservoir between well logs and elastic properties of AVO inversion. By this accurate relation, the fluid enrichment and fluid type are both identified. The case study results not only prove a practical applicability of the method in predicting the fluid distribution in carbonate reservoir, but also provide a new way for fluid prediction in carbonate reservoir by taking full advantage of pre-stack seismic data.
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An Improved Porosity Inversion Method Based on Gassmann Equation and Cross Examination on Results of Fluid Prediction
More LessSummaryBased on the newest research, the fluid prediction precision is closely related to porosity. For the complex carbonate reservoir in Tarim Basin, China, the fluid prediction result is proven to be reliable only when the porosity reaches 6%. The new knowledge is usually neglected in conventional fluid prediction workflow, which leads the prediction result exits some unreliable information. The porosity data should be used to evaluate the reliability of fluid prediction result. However, conventional porosity inversion method based on statistical method is often of poor applicability and low accuracy for complex reservoirs. To solve this problem, an improved porosity inversion method is proposed in this paper. The advanced method is proven to be more accurate. Besides, this method not only takes a simple formula and has an explicit physical meaning, but also finds its great advantage in calculating the input parameters. It is worth noting that density data obtained from conventional pre-stack inversion is not accurate, therefore it cannot be used to calculate the input parameter βE (compression factor of fluid-saturated rock). Adding regularization constraints in the pre-stack inversion process can solve this problem. Applying porosity data to evaluating the reliability of fluid prediction result is effective.
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Consistent Uncertainty Quantification on Seismic Amplitudes
Authors L.D. Sandjivy, A. Shtuka, J.L. Mari and B. YvenSummaryAt the feasibility stage of a high level radioactive waste facility in the of the eastern Paris Basin, the French National Radioactive Waste Management Agency (Andra) is conducting innovative and extensive characterization of the Callovo-Oxfordian argillaceous rock (Cox) and neighbouring Oxfordian and Dogger limestones. High resolution 3D seismic data are used to model the distribution of mechanical and hydrogeological properties, of the geological formations. Assessing the reliability of the modeling is crucial for making decision on the design and implementation of the radioactive waste facility. The cornerstone of the model reliability assessment is to first address the reliability of seismic stacked amplitudes that are input to the geophysical inversion. Stochastic processing of the pre-stack amplitude gathers enables to compute a Spatial Quality Index (SQI) attached to stacked amplitude data. SQI can be considered as a reliable indicator of the preservation of true amplitude by the processing sequence. In the field example of the storage of radioactive waste in a safe geological shale environment, SQI helps validating the identification of lateral variations of shale content inside the target layer and of a high porous layer in the limestone just below
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Plea for Consistent Uncertainty Management in Geophysical Workflows to Better Support E&P Decision-making
Authors L.D. Sandjivy, A. Shtuka and F.A. MererSummaryDespite tremendous progress in acquisition and processing techniques, geophysical data sets continue to carry uncertainty impacting the performance of processing, interpretation and subsurface property modeling workflows. This paper is a plea for consistent uncertainty quantification and propagation throughout successive geophysical workflows (“Uncertainty Management”), in view of maximizing the performance of geophysical workflows and the reliability of static/dynamic reservoir models. The authors run through the mathematical framework applied to Uncertainty Management. They then explain how to build stochastic geophysical processes and how to implement them into standard geophysical workflows. An example is provided with focus on Gross Rock Volume (and P10, P50, P90 structural depth cases) computations in support of efficient prospect ranking and discovery appraisal. The achievement is to empower geophysicists, maximize the efficiency of E&P decision-making and contribute to sustainable and profitable Earth resource management.
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Stochastic Time-lapse Inversion of a CO2 Sequestration Synthetic Seismic Data
Authors M. Meira, R. Pevzner, E. Caspari and B. GurevichSummaryIn the domain of time lapse interpretation the development of tools to create scenarios that can explain the time lapse anomalies directly from the seismic data and, at the same time, evaluate the uncertainty associated with the available input data can help to accelerate the incorporation of this important information to flow simulations The purpose of this study is to investigate whether the time-lapse seismic inversion can detect changes of the seismic response caused by injection of distinct amounts (10,000 t and 30,000 t) of 80/20% CO2-CH4 mixture into sandstone reservoir in South Australia using synthetic seismic data. The number of realizations as well as the informed uncertainties of input parameters plays a big role in the unveiling of subtle effects of small volumes of injection as this one. The presented findings suggested that the current approach has succeeded in using synthetic data to test the limits of this recent technique.
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Risk Analysis Using Bootstrap in Combination with Inversion
More LessSummaryWe show in this paper a new approach to statistical risk analysis using the bootstrap method in conjunction with model based inversion. It is a posteriori approach combining the results of deterministic seismic inversion and rock physics analysis. It’s an effective and efficient way to manage drilling risk and uncertainty. We show an example from the Texas Gulf Coast and demonstrate its effectiveness.
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Geological and Drilling Risk Management for Geothermal Prospects
Authors R.H.B. Rijkers, N. Heijnen and R. te Gussinklo OhmannSummaryIn this paper a recommended work flow and methodology of geological and drilling risk management is shown with data of the Erica geothermal project in the Netherlands. For the detailed geothermal design and budget planning a geological risk study is carried out. The result of the geological setting, risk issues have been evaluated: depth, top reservoir, temperature, overpressure, water quality, salt plugging, residual gas residues, H2S and shallow gas.
Geological and drilling risks are identified and expected project risk can be calculated using risks analysis, expected probability by expert judgement and calculation of the risk with costs of possible measures or consequences. For geothermal significant financial reservation should be budgeted. A work flow with proposed scheme of risk calculation is shown in this paper.
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A Texture Synthesis Based Algorithm for Simulating Reservoir Models
Authors C. Gardet, M. Le Ravalec and E. GloaguenSummaryThe geological complexity of reservoir calls for multiple points statistics to represent curvilinear objects, which cannot be done with usual two-point statistics. Computer graphics algorithms and geostatistical multiple point algorithms share many ideas. They both refer to a training image depicting the expected geological architectures and produce images with the multiple point statistics inferred from the structural content of the training image. The difference is related to the ultimate purpose. In geostatistics, we aim to build realizations conditioned by hard data. In computer graphics, the idea is to reproduce textures that cannot be distinguished from natural textures by human eyes. Here, we present an texture synthesis algorithm modified to properly handle geological reservoir simulation. Various tests are performed to investigate how this approach can help reproducing geological objects (with similar shapes, connectivity, density, distribution, etc.). A few improvements are suggested to make the simulation algorithm more efficient and appropriate for reservoir modeling. We also tried to decrease the CPU-time without degrading the simulated image. Last, we present a few numerical tests focusing on training images describing porous media as well as geological formations with channels or faults.
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New Approach for the Generation of the Geological Conceptual Model with Limited Information, Understanding Green Fields
Authors R. Rodriguez Torrado, G. De Paola and S. EmbidSummaryGenerate a plausible geological model for a green-field as well as rank reservoirs with different level of associated uncertainty can be quite challenging. In this paper, we propose a new approach to generate predictive static models in the first stages of reservoir appraisal.
At this stage, structural, sedimentary and petro physical information is very limited. The workflow proposed aim to use any available information whether coming from analogues reservoirs and/or field-data to reduce uncertainty. Initially the structural uncertainty is characterized and propagated generating an ensemble of plausible scenarios based on the perturbation of structural types. Subsequently, a novel formulation is presented to define a conceptual sedimentary (optimum number and percentage of the facies) and petro-physical model for the generation of the 3-D geological plausible scenarios.
The methodology has been tested on the Brugge field benchmark modified as green-field. The proposed workflow yields a good approximation of the reservoir static and dynamic behavior (e.g. OOIP and NPV) compared with the original model. In addition, the sedimentary definition of the facies is well characterized with respect to the core interpretation from laboratory.
The new workflow presented allows to generate plausible geological scenarios with limited amount of information, quantifying and propagating the uncertainty.
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Cross-Verification of Adjoint and MCMC Workflows for Estimation of Prediction Uncertainties Including Historical Data
Authors R. Schulze-Riegert, I. Ajala, D. Awofodu, H. Almuallim, J. Baffoe, F. Chataigner, N. Kueck, O. Pajonk and A. ShiromizuSummaryReservoir simulation workflows leading from history to prediction are built on a number of alternative optimization and sampling techniques with different characteristics. Adjoint techniques derive analytical sensitivities directly from the flow equations of the simulator. In a model update step those sensitivities are used for property modifications on grid cell level. Derivative-free techniques like Markov Chain Monte Carlo are used for optimization and uncertainty quantification including history data. Both techniques are different in nature and support alternative modelling strategies like local vs. global, deterministic vs. stochastic. In this work we apply both techniques in alternative workflow designs to a recent “hierarchical benchmark case study for history matching, uncertainty quantification and reservoir characterisation”. An implementation of an adjoint technique is applied for analytical sensitivity calculations and local adjustments of rock properties in a history matching workflow. Markov Chain Monte Carlo is used for global optimization and uncertainty quantification. Well production data is used in the model calibration phase and history matched simulation models are carried forward to prediction. Both methods are used for cross-verification of prediction results.
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Frequency-domain Iterative Solver for 3D Acoustic Wave Equation with Two-stage Semi-analytical Preconditioner
Authors D. Neklyudov, M. Dmitriev, M. Belonosov and V. TcheverdaSummaryAn approach to iterative solution of 3D acoustic wave equation in the frequency domain is introduced, justified and verified numerically. It is based on special one- and two-level preconditioners, which are constructed by means of inverse operator for complex damped Helmholtz equation with a depth dependent coefficient. An essential element of the process is computing how these preconditioners acts on a 3D vector. This computation is achieved by performing 2D Fast Fourier Transform along lateral coordinates, followed by solving a number of ordinary differential equations with respect to depth. Both of these operations are effectively parallelized, thus allowing efficient computation. For media with strong lateral variations, such preconditioner can be applied in two stages to increase the rate of convergence. Results of numerical experiments demonstrate good accuracy and acceptable computation times.
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Fast Solution of Time-Harmonic Wave Equation for Full-Waveform Inversion
Authors R.L. Lago, A.P. Petrenko, Z.F. Fang and F.H. HerrmannSummaryFor many full-waveform inversion techniques, the most computationally intensive step is the computation of a numerical solution for the wave equation on every iteration. In the frequency domain approach, this requires the solution of very large, complex, sparse, ill-conditioned linear systems. In this extended abstract we bring out attention specifically to CGMN method for solving PDEs, known for being flexible (i.e. it is able to treat equally acoustic data as well as visco-elastic or more complex scenarios) efficient with respect both to memory and computation time, and controllable accuracy of the final approximation. We propose an improvement for the known CGMN method by imposing a minimal residual condition, which incurs in one extra model vector storage. The resulting algorithm called CRMN enjoys several interesting properties as monotonically nonincreasing behaviour of the norm of the residual and minimal residual, guaranteeing optimal convergence for the relative residual criterion. We discuss numerical experiments both in an isolated PDE solve and also within the inversion procedure, showing that in a realistic scenario we can expect a speedup around 25% when using CRMN rather than CGMN.
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Effective Elliptic Models for Efficient Wavefield Extrapolation in Anisotropic Media
Authors U. Waheed and T. AlkhalifahSummaryWavefield extrapolation operator for elliptically anisotropic media offers significant cost reduction compared to that of transversely isotropic media (TI), especially when the medium exhibits tilt in the symmetry axis (TTI). However, elliptical anisotropy does not provide accurate focusing for TI media. Therefore, we develop effective elliptically anisotropic models that correctly capture the kinematic behavior of the TTI wavefield. Specifically, we use an iterative elliptically anisotropic eikonal solver that provides the accurate traveltimes for a TI model. The resultant coefficients of the elliptical eikonal provide the effective models. These effective models allow us to use the cheaper wavefield extrapolation operator for elliptic media to obtain approximate wavefield solutions for TTI media. Despite the fact that the effective elliptic models are obtained by kinematic matching using high-frequency asymptotic, the resulting wavefield contains most of the critical wavefield components, including the frequency dependency and caustics, if present, with reasonable accuracy. The methodology developed here offers a much better cost versus accuracy tradeoff for wavefield computations in TTI media, considering the cost prohibitive nature of the problem. We demonstrate the applicability of the proposed approach on the BP TTI model.
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Efficient and Accurate Numerical Wave Propagation
By B. QinSummaryTime domain Finite-difference (FD) methods are preferred in 3D seismic modeling and inversion because of their efficient use of memory and ease of implementation. However, they are still expensive computationally. To increase their efficiency without decreasing accuracy is an ever-present problem. In this abstract, we derive accurate two-step explicit marching formulae with source term for large time propagation steps. We then point out for specific problems, the appropriate manner to decide the temporal numerical scheme, and the biggest suitable time step, all for getting most effective-cost numerical wave propagation.
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3D Acoustic Wave Modelling with a Globally Optimal Finite-difference Scheme Based on Least Squares
More LessSummaryHigh-order finite-difference (FD) methods have been widely used in numerically solving seismic wave equations. Under the same accuracy, the least square-based (LS) optimal FD method for the 3D acoustic wave equation can improve the computational efficiency compared with the Taylor series expansion-based FD method. To increase the efficiency further, we introduce the scheme of adaptive variable-length spatial operators. The hybrid absorbing boundary condition is adopted to suppress the artificial reflections caused by the finite boundary. Dispersion analysis and modelling examples demonstrate advantages and accuracy of the LSM.
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One-step Lowrank Wave Extrapolation
Authors G. Sindi and T. AlkhalifahSummaryWavefield extrapolation is at the heart of modeling, imaging, and Full waveform inversion. Spectral methods gained well deserved attention due to their dispersion free solutions and their natural handling of anisotropic media. We propose a scheme a modified one-step lowrank wave extrapolation using Shanks transform in isotropic, and anisotropic media. Specifically, we utilize a velocity gradient term to add to the accuracy of the phase approximation function in the spectral implementation. With the higher accuracy, we can utilize larger time steps and make the extrapolation more efficient. Applications to models with strong inhomogeneity and considerable anisotropy demonstrates the utility of the approach.
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Geophysical Simulation with High-accuracy FDM Multiblock and Hybrid Techniques
Authors I.L. Sofronov and L. DovgilovichSummaryChallenges in current geophysical modelling arise from complex structural features of reservoirs including high-velocity deep zones, near-surface phenomena (e.g., karst, low-velocity surface sediments, fractured zones), extreme topography, rapid lateral variations, etc. Previously, we proposed using curvilinear grids in frames of the multiblock technique for an efficient approximation of structural and velocity features of the reservoir by finite-difference discretizations. Recently, we improved the approach in essentially three areas: 1) much more accurate and faster difference schemes inside each block based on the summation-by-parts approach (namely, fourth order accuracy on interfaces instead of the second order and the eighth order inside blocks instead of sixth); 2) a nonmatched grids technique in adjacent blocks for the option of step-type grid refinement/coarsening; 3) the possibility of coupling adjacent blocks discretized by finite differences and by spectral elements method (SEM) schemes, i.e., a hybrid technique of finite difference methods (FDM) and SEM. These features permit us to achieve high accuracy, performance, and flexibility with the novel hybrid multiblock technique by combing advantages of its components – FDM and SEM.
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A Robust Absorbing Layer Method for Seismic Wave Simulation in Anisotropic Media
Authors L. Metivier, R. Brossier, S. Operto and J. VirieuxSummarySeismic wave modeling requires using adapted boundary conditions to simulate infinite or semi-infinite media. Because of its efficiency, the Perfectly Matched Layers (PML) method has rapidly become the standard for acoustic and elastic propagation. However, PML are not adapted to anisotropic media for which the method becomes amplifying. Alternative methods have to be designed. In this study, we present the SMART layer method, which relies on a diagonal decomposition of the hyperbolic operator. The method is not perfectly matched, therefore less efficient than the PML method, however it is proved to remain dissipative, even for anisotropic media. We apply the method to the acoustic TTI equations. We present numerical results on a homogeneous test case and on the BP 2007 model, which includes a space dependent tilt angle. We compare the SMART and the PML methods. The results emphasize the robustness of the SMART method: no wave amplification is observed. In addition, the accuracy of the PML can be reached at the expense of an increase of the SMART layer width. The additional computational cost is compensated by the simple form of the SMART layer: only a zero-order term is added to the equations and no additional variables are required
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Geothermal and Hydrocarbon Exploration - The Double Play Synergy
Authors J.D. van Wees, L. Kramers, H. Mijnlieff, S. De Jong and B. ScheffersSummaryThere is a clear synergy possible in geothermal and hydrocarbon exploration if wells are targeted in a double play concept. In the Netherlands, clastic aquifers which have been explored extensively by the hydrocarbon industry and are now targeted for geothermal energy qualify well for a double play. Through a simple example we demonstrate quantitatively the benefit of the double play in monetary risk and reward of an exploration project. Furthermore, we evaluated the potential effects of synergy for a synthetic portfolio of gas prospects in the Netherlands.
It is shown that the potential benefits may be considerable and can lead to approximately 7 BCM additional gas being produced, and in the order of 10 geothermal doublets being developed.
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Reservoir Modelling of Lower Cretaceous West Netherlands Basin Aquifers for Geothermal Energy Production
Authors C.J.L. Willems, G.J. Weltje, M.E. Donselaar and D.F. BruhnSummaryThis project aims to predict Lower Cretaceous reservoir architecture and reservoir properties of the graben blocks in the West Netherlands Basin for low enthalpy district heating geothermal energy.
Horst and pop-up structures in the study area were targets of oil and gas production in the last 60 years. For the recent upcoming geothermal energy production the focus lays on the deeper and warmer graben structures in between the oil and gas fields. Reservoir property predictions like thickness and permeability are currently based on interpolations between oil and gas well measurements on horst and pop-up structures. In order to successfully produce from the current 45 geothermal licences in the province of Zuid-Holland, detailed reservoir models and associated uncertainty maps of the Lower Cretaceous sandstones are required.
Goals of the project are to model the reservoir architecture in order to simulate production and determine optimal well placement of geothermal doublets and predict possible doublet interference. Reservoir architecture of these sandstones will be studied by re-evaluating the existing lithostratigraphically based well log correlations, in combination with seismic interpretation and core studies. A palinspastic reconstruction is carried out on a cross section to indicate the paleotopography and the complex reservoir architecture.
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Extended Geothermal Potential of Clastic Aquifers by Hydraulic Stimulation
Authors J.G. Veldkamp, M.P.D. Pluymaekers and J.D.A.M. van WeesSummaryWe evaluated the implications of hydraulic stimulation in a Dutch context for low permeability clastic aquifers at a depth of 2000 to 4000 m, whose transmissivity has been mapped in the framework of the Dutch subsurface information system on geothermal energy in the Netherlands. For the simulation and well layout we adopt long horizontal well trajectories up to 2 km length with vertical fracs along the well bore. The implications on subsurface potential are significant as it unlocks considerable clastic aquifer potential. Our calculations indicate that hydraulic stimulation is capable of producing higher flow rates and power than without stimulation with moderate excess in LCOE and extending in depth and spatial extent the potential. The LCOE for the reservoir stimulation scenario can stay well below 12–13 EUR/GJ, depending on natural permeabilities which need to be in excess of 0.5 Darcymeter.
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An Example of Synergy between Hydrocarbon and Geothermal Energy Production in the Netherlands
Authors E. Peters, S.F. van Gessel and F. Jedari EyvaziSummaryAfter the successful development of a geothermal site in 2007 in the Netherlands, interest in geothermal development has increased. The large amount of data gathered for the hydrocarbon industry shows good potential in the north of the Netherlands often in the same areas in which hydrocarbon production occurs. However, concerns about interference between the two activities have also increased. We will show a case study of the concurrent production from a gas field and a geothermal doublet. The geothermal doublet is located in an active aquifer, that is in hydraulic connection with the gas field. The case study is based on the Roden field, which is a typical Rotliegend gas field in the north of the Netherlands. A reservoir simulation model was created in which the aquifer is simulated explicitly. The gas field is produced from two wells and a geothermal doublet is located in the aquifer at a distance of 500m from the gas field. The presence of the geothermal doublet increased the field cumulative gas production by 3.3% from 6.65 bcm to 6.87 bcm. The presence of the geothermal producer delayed the water breakthrough in one of the production wells, increasing the field life by about a year.
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