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82nd EAGE Annual Conference & Exhibition
- Conference date: October 18-21, 2021
- Location: Amsterdam, The Netherlands
- Published: 18 October 2021
81 - 100 of 1137 results
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Multicomponent 3D-3C Data Acquisition and Processing in the Bandurria Norte Concession, Neuquén Basin, Argentina
More LessSummaryHydraulic well stimulation requires knowledge of rock mechanical parameters to reduce uncertainty attached to development of shale oil prospects. Multicomponent 3D-3C seismic data provide more reliable estimation of rock physical parameters needed for fracture stimulation in low permeability unconventional reservoirs. The design and processing of a special 3D-3C seismic survey in the Bandurria Norte concession is illustrated, whereby the Jurassic/Cretaceous Vaca Muerta Formation interval is the main target.
Seismic characterization of unconventional reservoirs necessitates: 1) high resolution input data with a high trace-to-trace correlation, 2) high signal-to-noise ratio, 3) reliable amplitudes and 4) preserved post-migration azimuthal information. Multicomponent seismics make analysis of seismic anisotropy and shear wave splitting possible. The PP-PS joint inversion scheme generates more accurate elastic properties (e.g. Young’s modulus). For these reasons, a static cable-less acquisition spread of 600 three-component (3C) receivers was laid out during the standard P-wave seismic acquisition in the Bandurria Norte Block. The multicomponent data was successfully processed and interpreted. Estimation of shear wave splitting effects improves the velocities with a positive impact on the PreSTM imaging. Directional dependency of the seismic velocities is thought related to fracture distribution and local stress regime.
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What is the Benefits of Carbonated Water Injection in Heavy Oil Reservoirs: A Case Study
Authors M. Shokriafra, H. Norouzi, B. Rostami and P. AbolhosseiniSummaryAdvantage of CWI over WI and CO2 injection for an Iranian heavy oil reservoir, is studied through core flooding experiments. Five different experiments were conducted in different wettability states using secondary and tertiary injection scenarios. The results showed that CWI is more beneficial than WI and CO2 injection. Higher sweep efficiency, more stable front, CO2 diffusion to oil and subsequent oil viscosity reduction and swelling are the reasons for better CWI performance. Moreover, due to the lower sweep efficiency of WI and low resistance channels created along the flow axis, tertiary CWI is not capable to recover all the bypassed oil, so its recovery is less than secondary CWI. The results of aged experiments indicated that by shifting wettability toward mixed wet, CWI performance decreased in both WI and secondary CWI. In mixed wet wettability several pores which were accessible for injection fluid in clean sand, are not reachable in aged sand anymore which accelerated injection fluid breakthrough and decreased ultimate recovery. Besides, it was observed that the proportion of recovery after breakthrough to the total recovery was increased for SCWI while decreased for WI, this is attributed to the acidic nature of carbonated water and consequent wettability alteration.
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A Multi-Axial Perfectly Matched Layer for Finite-Element Time-Domain Simulation of Elastic Wave Propagation
More LessSummaryWe develop a novel M-PML absorbing boundary condition for the second-order finite-element elastic wavefield simulation. We first derive the M-PML formulation and then incorporate the M-PML into the second-order wave formulation in the time domain with fewer split terms to reduce memory requirement and consequentially improve the computational efficiency. Numerical wavefield simulations are carried out to demonstrate the stability and efficiency of the proposed M-PML. The proposed algorithm can also be extended to 3D anisotropic elastic simulation of wave propagation with reasonable efforts.
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A Novel Nonlinear Joint AVA Inversion Method for Russell Fluid Factor
More LessSummaryFluid factor, as an important characterization parameter for reservoir fluid identification, is mainly estimated by the inversion methods based on the linear approximations of Zoeppritz equations. For complex hydrocarbon reservoirs, the calculation accuracy of the linear approximate formulas is low, which greatly limits the estimation accuracy of the fluid factor. To solve this problem, a nonlinear fluid factor inversion method directly based on the Zoeppritz equations is presented in this abstract. Firstly, based on poroelasticity theory, we performed several substitutions to convert the Zoeppritz equations from the classical form to a new form containing the chosen fluid factor, shear modulus and density (FMR). Then, the objective function was constructed using the new equations in a Bayesian framework. The Cauchy and Gaussian distributions were used for a priori distribution and the likelihood function, respectively. Lastly, the nonlinear objective function was solved by using the Gauss-Newton method. Both synthetic and field data show that the proposed method can stably estimate the fluid factor with high accuracy, and the accuracy is higher than that of the method based on Russell approximate formula.
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Nonlinear AVA Inversion Based on Bayesian Theory for VTI Media
More LessSummaryFor shale reservoirs with VTI anisotropy characteristic, the inversion methods based on linear approximate formulas are commonly used to estimate the elastic parameters and anisotropy parameters. However, the calculation accuracy of linear formulas is low, which limits the estimation accuracy of these parameters. In fact, the linear approximation formulas are made up of isotropic and anisotropic terms. Numerical experiments show that if we use the exact Zoeppritz equations to replace the isotropic term in these formulas, the calculation accuracy of reflection coefficients can be improved. This can reduce the influence of the calculation error introduced by the forward operator on the inversion result. Therefore, in order to improve the estimation accuracy of reservoir parameters, we constructed a Bayesian nonlinear inversion objective function based on the combined equation obtained by substitution. In addition, the differentiable Laplace distribution blockiness constraint term was also added to the Cauchy background prior model to further improve the vertical resolution of inversion results. Synthetic data test shows that the proposed method can not only inverts Thomsen anisotropy parameters stably, but also accurately estimates the vertical P- and S- wave velocities and density, which demonstrates the effectiveness of this method.
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Ambient Noise Reverse Time Migration Based on Velocity Flood for Fault Imaging
More LessSummaryWe propose a novel ambient noise Transmitted Surface Wave Reverse Time Migration (TSW-RTM) method to image interfaces of fault zones where the crystalline basement rocks truncate against the surrounding sediments. The source and receiver wavefields are propagated in the sediment flood velocity and crystalline flood velocity, respectively. The migrated image is then obtained by applying the zero-lag cross-correlation imaging condition to the forward and backward wavefields. The synthetic test demonstrates that the transmitted surface wave can provide sufficient information to form correct images at the fault surface. We then apply the proposed TSW-RTM method to image a major fault of Tanlu fault Zone near Chao Lake in eastern China, using the surface wave retrieved from the ambient noise data. Compared with the conventional ambient noise tomography method, our method provides a better imaging result with much higher resolution and certainty where both the interface position and dipping angle of fault are well consistent with the previous study. This novel ambient noise imaging method enables us to image the fault interfaces without a priori information of the fault position, which is especially useful in the study areas that are less illuminated by seismic surveys or earthquake events.
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Elastic Least-Squares Reverse Time Migration in the Rugged Seabed Structure
More LessSummaryThe marine deep water is rich in oil and gas resources. However, the severe rugged seabed structure brings great difficulties to seismic imaging in the marine environment. To accurately image the target layer under the rugged seabed interface, an elastic least-squares reverse time migration (LSRTM) in the rugged seabed structure is proposed. This method is based on a coupled equation method, which uses the acoustic wave equations in seawater and the elastic wave equations in the underlying elastic medium. The pressure and the stress are transmitted steadily and continuously by using the acoustic-elastic control equation at the seabed interface. To overcome the influence of the rugged seabed interface, the acoustic-elastic model is meshed into non-uniform curvilinear grids, and the corresponding mapping technique is used to transform the model with the rugged seabed interface to a horizontal one in the curvilinear coordinate system through the coordinate transformation. Therefore, in this paper, we overcome the limitations of the traditional finite difference method in imaging the rugged seabed structure environment caused by its regular rectangular grid generation, and proposed the LSRTM method of the acoustic-elastic coupled medium. Finally, the method of this paper was tested by a typical model trial.
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P-Wave Anisotropy Estimation from 3D VSP Data Acquired with Geophones and DAS at Otway Site
Authors S. Popik, R. Pevzner and A. BonaSummaryStage 2C of the Otway Project involves monitoring of a small-scale (15 kt) CO2-injection using an extensive time-lapse active seismic program. The main components of this seismic monitoring program are 4D surface seismic and 4D VSP surveys acquired before, during and after the injection. Data analysis reveals significant seismic anisotropy of the subsurface, which needs to be estimated and taken into account to improve the quality of imaging with both VSP and surface seismic data.
A wide range of offsets obtained during fifth monitoring survey of the project provides a unique opportunity for anisotropy estimation from 3D VSP data. In this study we compare geophone and Distributed Acoustic Sensor (DAS) VSP data and their applicability for anisotropy analysis. Analysis of DAS data gives anisotropy parameters for the entire depth of the well.
We estimate P-wave anisotropy by analyzing direct-wave VSP arrival times. The study demonstrates significant presence of both polar and azimuthal anisotropy. While vertical-plane anellipticity remains almost constant at 0.1 level for the whole depth range, azimuthal anisotropy changes significantly with depth: from negligibly small in the shallow part with significant increase below the 600 m depth, which most probably indicates the change of stress field at this depth.
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A Comparison of Predicted and Actual Reservoir Quality of Geothermal Projects in the Slochteren Formation
Authors L. Borst, N. Buik, W. Van Leeuwen and N. ShawSummaryNow that four geothermal projects have successfully been completed in the Slochteren Formation, the formation has proven as a valid aquifer for geothermal heating purposes. Before drilling a project, the local reservoir parameters need to be determined in order to determine the economic feasibility of a project. However, predicting this is not an easy task: permeabilities are often strongly overestimated, while temperatures and (net) reservoir thicknesses are often underestimated. This has several causes: first, the available resources for geothermal projects are limited. Therefore, geothermal feasibility studies need to be done with limited amount of time using publicly available data, mostly from hydrocarbon wells. Second, these hydrocarbon wells are drilled with a different objective than geothermal wells, which introduces difficulties when translating the datasets into one another. Thirdly, not all planned geothermal project locations have a high density of well data, which can introduce a large uncertainty in interpreted reservoir properties. As a result, comparing data from these indicative studies to the actual results after drilling of the well discloses certain discrepancies. This study helps to understand where these discrepancies come from, and may improve the accuracy of the estimated geothermal doublet performance on basis of hydrocarbon well data.
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Rock Physics Modelling of Gas Dissolved in Water Sandstone, Nakajo Field, Japan
Authors T. Fukano, T. Mizukami, T. Aoyama and Y. MaeharaSummaryNatural gas dissolved in water (GDW) is a common form of hydrocarbon occurrence in Japan, and gas production from the GDW accounts for 17% (approximately 290 mmscf/day) of total natural gas production in the country. Nakajo field is one of the fields which has long production history from the GDW reservoir. However, as GDW sandstone itself has not been well understood in aspect of the petrophysics and rock physics behaviour, it was a new finding for us that gas-effect and gas-effect-like sonic responses were observed in the GDW sandstone. In this paper, we show result of rock physics modelling, fluid substitutions, synthetic seismogram calculations, wedge modelling and AVO modelling for GDW sandstone. The rock physics modelling results revealed presence of isolated gas in GDW reservoir. Besides, water saturation estimated from rock physics modelling was regarded as useful tool to detect GDW reservoir with gas isolation. An application to seismic data is also encouraged according to synthetic seismogram calculations and AVO modelling. These outcomes allow a better evaluation approach of the surrounding area where future exploration and development potential may exist.
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Role of Prolonged Successive Fluid Flow on the Performance of Relative Permeability Modifiers in Gas Reservoirs
Authors F. Alshajalee, M. Seyyedi, M. Verrall, C. Wood and A. SaeediSummaryExcessive water production is becoming common in many petroleum reservoirs. Relative permeability modifiers (RPM) have been used to disproportionately reduce water permeability (DPR) with minimum effect on the gas/oil phases. This manuscript reports the results of an experimental study where we examined the effect of prolonged successive water-gas injection on RPM’s performance in gas/water system. The results show that the volume of water coming in contact with the polymer-treated porous medium has a direct impact on the extent of polymer swelling and thus the water permeability of the medium. It was also shown that over a large volume of gas injection, treated porous medium presents a better permability for gas at later times compared to the early times of injection. The reason could be the dehydration of the polymer layer adsorbed to the pore surfaces of the medium. It was found that successive water-gas injection could lead to stronger performance of polymer towards reducing water permeability, but it comes with the cost of a further reduction in gas relative permeability.
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Seismic Noise Attenuation Based on Higher-Order Directional Total Variation
More LessSummaryNoise attenuation is one of the key problems in seismic data processing. Total variation (TV) has played an important role in seismic data denoising and reconstruction. We develop a high-order directional total variation method for seismic data denoising that considers the structural direction of the seismic data. It involves a parameter to balance higher-order derivatives, thereby reducing the staircasing effect of the bounded variation functional. We test the method on a model where the data are contaminated by different types of noise. The corresponding denoising performance is compared with the TV and conventional directional total variation method from two aspects of signal-to-noise ratio and effective signal leakage degree. The model test and field data application illustrate the advantage of this functional as a regularization term for seismic noise attenuation.
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Squeezed Diapirs of the Timan Pechora Basin: Structure, Evolution and Petroleum Prospectivity
Authors K. Sobornov, I. Korotkov, K. Kudryavtsev and R. AnisimovSummaryReprocessing and integrated interpretation of vintage and newly available data provided new insight into structural framework of thrust belt in the northeastern part of the Timan Pechora basin. It showed that structural evolution of the fold and thrust belt was influenced by the multiphase development of salt diapirs which finally were squeezed during pulses of the orogenic shortening. This was accompanied with expulsion of salt and the development of divergent thrusting. The improved seismic imaging has allowed for more accurate definition of the structure and stratigraphy below thrust sheets including salt sole in frontal zone of the fold and thrust belt. The updated interpretation shows new exiting opportunities for petroleum exploration provided by subsalt traps.
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Stratigraphic Forward Modelling Applied to Reservoir Characterisation of Pre-Salt Carbonate Reservoirs, Santos Basin, Brazil
SummaryThis work proposes the use of stratigraphic forward modelling to test and quantify concepts about the evolution of the carbonate platform of a Pre-Salt field, as well as to use the results as trends for stochastic simulations of facies in geocellular reservoir models. The facies model was performed in three steps: (1) facies interpretation in the wells using rock data (core and sidewall samples) and image logs; (2) forward modelling simulation to control the carbonate reservoir geometry and low-frequency heterogeneities; (3) stochastic simulations of the facies, which aims to generate a high-frequency variability of facies and honour the well data. Subsequently, this final facies model, based on geological knowledge and geostatistic approach, will be the background for the propagation of the petrophysical rock properties (porosity and permeability).
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Characterization and Modeling of the Vug and Fracture Network Affecting a Carbonate Reservoir (Kmz - Mexico)
SummaryThe Cretaceous reservoir of the KMZ field consists of brecciated, carbonate rocks characterized by the presence of a complex system of natural fractures and solution vugs. As this high-permeability system plays a major role on the fluid circulation in the field, it is crucial to build-up a 3D model in order to quantify its dynamic impact. To do this, we applied the methodology for the analysis of fractured reservoir FracaFlowTM developed by the IFPEN/Beicip-Franlab group, integrating BHI data, structural information (3D seismic) and dynamic data.
Both diffuse and fault-related fractures were recognized in the field, whereas vugs largely affect mainly the brecciated layers of the reservoir. The innovation of the present study is the modeling of the vugs, with the software FracaFlowTM, as independent objects overprinting the matrix properties and distributed independently from fractures. This allows to take into account and calibrate separately the permeability of the vugs and fractures.
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Seismic Acoustic Impedance Estimation by Learning From Sparse Wells via Deep Neural Networks
Authors H. Di, X. Chen, H. Maniar and A. AbubakarSummarySeismic acoustic impedance is one of the most important properties closely related to the subsurface geology, and thus robust acoustic impedance estimation from seismic data is an essential process in subsurface mapping and reservoir interpretation. For compensating the limited bandwidth in seismic data, one feasible approach is to integrate 3D seismic volume with 1D wells that are usually sparsely distributed within a seismic survey, and such integration aims at finding the optimal non-linear mapping function between them. Most of the existing mapping methods, particularly these powered by machine learning, are performed in 1D and/or require down-sampling of well logs to the seismic scale, which run of the risk of limiting the estimation valid only around the training wells and fail to provide consistent prediction throughout the entire seismic survey.
We present a semi-supervised learning workflow for estimating the acoustic impedance over a given seismic survey by learning from a small number of sparsely-distributed wells via two deep neural networks. Applications to the synthetic SEAM dataset of a complex salt intrusion demonstrates its capability in reliable seismic and well integration, particularly in the zones of poor seismic signals due to the presence of geologic complexities, such as saltbodies.
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Diffraction Separation and Holistic Migration: High-Resolution Imaging Beyond Nyquist
Authors L. Gelius and V. Stenbekk ThorkildsenSummaryIn case of a broken hologram, an image of the complete object can still be obtained from one of the fragments. The reason is that each diffraction point of the object sends out waves that reach every point on the hologram. As an analogy, we propose to separate diffractions from standard seismic reflection data. The use of a decimated version of such data (violating the Nyquist sample condition) should still contain all necessary information to obtain an image of the finer details of the subsurface employing the concept of holographic migration. The feasibility of the proposed approach is supported by a field data example from the Barents Sea.
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Langevin Dynamics Markov Chain Monte Carlo Solution for Seismic Inversion
Authors M. Izzatullah, T. van Leeuwen and D. PeterSummaryIn this abstract, we review the gradient-based Markov Chain Monte Carlo (MCMC) and demonstrate its applicability in inferring the uncertainty in seismic inversion. There are many flavours of gradient-based MCMC; here, we will only focus on the Unadjusted Langevin algorithm (ULA) and Metropolis-Adjusted Langevin algorithm (MALA). We propose an adaptive step-length based on the Lipschitz condition within ULA to automate the tuning of step-length and suppress the Metropolis-Hastings acceptance step in MALA. We consider the linear seismic travel-time tomography problem as a numerical example to demonstrate the applicability of both methods.
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A New Integrated Workflow to Generate Avo Feasibility Maps for Prospect De-Risking
Authors P. Avseth, I. Lehocki, K. Angard, T. Hansen, E. Shelavina and S. SchjelderupSummaryA new integrated workflow for generation of AVO feasibility maps to be used in prospect de-risking is presented. We demonstrate the workflow on data from the Barents Sea. The methodology enables rapid extrapolation of expected rock physics properties away from well control, along selected horizon, constrained by seismic velocity information, geological inputs (basin modelling, seismic stratigraphy and facies maps) and rock physics depth trend analysis. The workflow should allow for more rapid, seamless and geologically consistent DHI de-risking of prospects in areas with complex geology and tectonic influence. The AVO feasibility maps can furthermore be utilized to generate non-stationary training data for AVO classification.
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Rock Physics Analysis of Volcanic Lava Flows and Hyaloclastites
Authors P. Avseth, J. Millett, D. Jerram, S. Planke and D. HealySummaryA study is conducted to investigate the rock physics properties of volcanic facies from available core measurements (72 samples available from Iceland and Hawaii). The main goal is to investigate the rock physics properties of a set of volcanic rock samples, and to establish predictive rock physics templates for these rocks, as a function of facies and rock texture, fluids and minerology. We focus on lava flows and hyaloclastites from Iceland and Hawaii. We find that both these facies can be modelled using modified Hashin-Shtrikman upper elastic bounds, and we create rock-physics templates for varying porosity and fluid saturations. Dry or gas-filled hyaloclastite facies plots with low acoustic impedances and low Vp/Vs ratios and are nicely separated from brine-filled hyaloclastites. Dry and wet high-porosity/high-permeability vesicular lavas will have similar AI and Vp/Vs values, and therefore these rocks will be more difficult to discriminate seismically.
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