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78th EAGE Conference and Exhibition 2016
- Conference date: May 30, 2016 - June 2, 2016
- Location: Online
- Published: 30 May 2016
1 - 50 of 1034 results
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A High-resolution Weighted Semblance for Dealing with AVO Phenomenon
Authors S. Ebrahimi, A. Roshandel Kahoo, Y. Chen, M.J. Porsani and W. ChenVelocity analysis employs coherency measurement along a hyperbolic or non-hyperbolic trajectories time window to build velocity spectra. Accuracy and resolution are strictly related to the method of coherency measurements. Semblance has poor resolution velocity which affects its ability to distinguish distinct peaks. The problem of traditional semblance are two folds: low resolution and inability of handling AVO phenomenon. Although the AB semblance method can peak velocities in area with AVO anomaly, it has a lower resolution than conventional semblance. In this paper, we proposed a weighted AB semblance method that can handle the two problems simultaneously. We introduced new weighting functions to the AB semblance in order to enhance the resolution of velocity spectra in time and velocity axis. The first weighting function is defined based on the ratio between the first and second singular values of the time window in order to improve the resolution of velocity spectra in velocity axis. The second weighting function is based on the position of seismic wavelet in time window and can enhance the resolution of velocity spectra in time axis. We use both synthetic and field data examples to show the superior performance of the proposed approach over traditional approaches.
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Study of the Casing Effect on Borehole-to-surface Onshore CSEM
Authors E. Vilamajó, V. Puzyrev, P. Queralt, A. Marcuello and J. LedoSummaryMonitoring the resistivity changes occurred in reservoirs during hydrocarbon production or CO2 sequestration is essential to determine fluid distribution and to optimize resources and efforts. Several modeling or theoretical studies have demonstrated the capability of the CSEM method to monitor onshore reservoirs. However there exist few published studies reporting experimental results from real CSEM experiments. Realistic modeling studies are needed to understand real data and to identify and characterize different effects affecting them. In this paper we investigate the sensitivity of the borehole-to-surface configuration using a deep VED. In order to study the influence of the source position and the effect of the steel casing on the data, we present numerical examples and a comparison with real results. The effect of the casing has been studied from two different approaches: a realistic modeling of the casing or replacing the casing by dipoles simulating the current induced along the casing. Both approximations can qualitatively reproduce the experimental data. In the first case, the vertical separation of the VED and the bottom of the casing is the key factor to be determined. In the second case, a precise determination of the current induced in the bottom of the casing is required.
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3D Inversion of Controlled-source Electromagnetic Data in the Presence of Steel-cased Wells
Authors K. Tietze, C. Patzer, O. Ritter, P. Veeken and B. VerboomSummaryControlled-source electromagnetic (CSEM) methods are investigated for their applicability to monitor fluids in a German oilfield, where injected brines have much lower electrical resistivity than oil. In spring 2014, a borehole CSEM survey (4 transmitters, 25 MT-stations) was conducted across the oil-field including a new horizontal-vertical source using the steel-casing of a 1.3km deep abandoned oil-well for current injection. The survey was repeated in autumn 2015, expanded by measurement of the vertical electric field with a newly developed sensor in a 200m deep observation borehole.
Steel-cased wells in the oilfield influence the propagation of electromagnetic fields in the subsurface and cannot be neglected in CSEM modelling. Since horizontal dimensions of well casings are very small compared to their vertical extent, discretising boreholes as conductivity anomalies of the subsurface becomes computationally prohibitive. To tackle the modelling problem, we extended an integral equation method and describe the influence of steel-casings by equivalent source currents which generate a secondary primary field. The new approach allows to include steel-cased wells into our modelling codes, including interaction between multiple wells. We demonstrate the effect of steel-casings on CSEM responses and sensitivity of 3D inversion. Finally, the new inversion method is applied to the field data.
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Field Distortion Due to Surface Pipes in Surface to Borehole Electromagnetic
By N. CuevasSummarySurface to borehole (STB) and borehole to surface (BTS) EM measurements are expected to provide useful resolution of the oil/water contact at reservoir depth. It has been shown however that the effect of the vertical steel casing above the reservoir can yield a distortion of the fields due to current channeling and leakage away from the casing. This paper extends the analysis of casing effect to investigate the channeling arising when the exciting source induces currents in pipes that extend horizontally in front of dipolar antennas. The problem considers a halfspace system (air-sediments or seawater-sediments), a pipe buried in the lower medium extending along the Y axis and a horizontal dipole source embedded in the upper medium. The problem is treated in a semi-analytical formulation, providing a general framework to study the current channeling effect in the pipe and in turn to compute the secondary vertical electric and magnetic field arising downhole due to an exciting dipole source oriented in the X and Y direction.
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Calculating the Effect of Multiple Steel Cased Deviated Wells on Electromagnetic Surveys
Authors C. Kohnke, F. Lavoué, R. Streich and A. SwidinskySummaryElectromagnetic methods are sensitive to conductivity contrasts in the subsurface. This makes the methods useful for monitoring oil and gas reservoirs, which will experience changes in electrical conductivity over their lifetime. In a modern production environment, such a survey would be completed in the presence of multiple deviated cased wells. Common well casing materials, such as steel, are very good conductors and can create a strong secondary electromagnetic field that contaminates the data at the receivers with unwanted signal. To resolve this problem, it is necessary to be able to accurately model the effect of the well casings on collected data.
In this paper, we make use of earlier casing modeling work using the Method of Moments and extend the approach to model the electromagnetic response of a group of deviated wells in a layered geology subject to a marine CSEM survey and produce a tool fit for practical applications. An illustrative example is used to show the electric fields calculated by a group of deviated wells in a layered marine geologic setting. Results show that most of the electromagnetic fields channeled by the horizontal wells into a thin resistor are unable to escape into the surrounding media.
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A Comparative Analysis of SP Data Inversion by Spectral, Tomographic and Global Optimization Approaches
Authors R. Di Maio, E. Piegari and P. RaniSummarySelf-Potential (SP) fields are natural fields that originate from various forcing mechanisms related to electrical, hydraulic, chemical and thermal gradients. Due to the complexity of the source mechanisms, inversion of SP data is not easy and motivates the development of suitable techniques depending on application field, which ranges from engineering and geotechnical investigations to geothermal and mineral explorations. In this work, quantitative interpretations of self-potential data are given when SP anomaly sources can be modelled by simple polarized bodies whose parameters have to be determined. In particular, a comparative analysis is performed for the solutions of three different methods based on high-resolution spectral analysis, tomographic approach and global optimization, respectively. The efficiency of each technique has been tested by finding depth, polarization angle and shape factor of the anomaly source on synthetic data generated by simple geometrical structures (like sphere, horizontal and vertical cylinder and inclined sheet) and on field examples. The study shows limits and potentialities of the investigated methods and suggests hybrid algorithms as suitable tools for an accurate and full characterization of the anomaly source.
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A New Generation of Vertical CSEM Receiver
Authors S.L. Helwig, W. Wood, B. Gloux and T. HoltenSummaryThe combination of a vertical dipole source and vertical dipole receiver has several advantages for measurements of subsurface resistivity in a marine environment. To fully exploit the capabilities of this methodology the receiver system needs to meet strict requirements with regards to verticality and noise levels. Previously existing receiver systems have met theses technical requirements, but at the cost of operational efficiency as the mode of operation for launch and recovery of has limited the efficiency during data acquisition. In this paper we present a new and operationally efficient receiver system capable of recording high quality vertical E-field data. To meet specifications development on the electronics and the mechanical structure of the unit has been critical.
We will detail key components of the system and present data examples from offshore testing of the system.
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MT Noise Suppression for Marine CSEM Data
Authors K.R. Hansen, V. Markhus and R. MittetSummaryWe present a simple and effective method for suppression of MT noise in marine CSEM data. The method can be applied to any CSEM data set where both electric and magnetic fields are measured, and does not require deployment of reference receivers. By applying the method to field data from the Barents Sea, we obtained a significant reduction of MT noise.
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A 2.5D Comparison between Two CSEM Methods
Authors Ø. Frafjord, K. Eide, A.M. El Kaffas, S.L. Helwig and T. HoltenSummarySeveral different CSEM technologies are currently commercially available for offshore exploration, with different characteristics and advantages. Few direct and realistic comparisons between the different methodologies have been made.
In this paper we use a 2.5D finite element code capable of handling both frequency domain and time domain to investigate potential for depth penetration for two methods, horizontal source frequency domain and vertical source time domain. Synthetic data with realistic noise levels has been generated for specific simple models and then inverted. Our results show that vertical time domain solution has potential to resolve deeper targets for the assumed conditions.
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Fast Pseudo-spectral Method for Wave Propagations
More LessSummaryNumerical simulations of elastic wave propagations are the critical components for seismic imaging and inversion. Finite-difference schemes yield high efficiency but fail to ensure the accuracy of the high wavenumber components. The pseudo-spectral algorithm is accurate up to the Nyquist frequency, and it is efficient because of the high level optimization of the fast Fourier transform (FFT) algorithm. The calculation of derivatives in elastic wave propagation could employ the success of FFT optimization. A conventional spectral method consists of three procedures: a forward real to complex (R2C) FFT, a multiplication of the derivative term, such as a for first derivatives, and a complex to real (C2R) inverse FFT. For any even number, the R2C FFT is actually utilizing a half-sized C2C FFT, and then a further spectral manipulation is employed to obtain the spectrum. We propose an efficient scheme to calculate the derivatives for elastic wave propagation in which we apply a forward C2C FFT, and then multiply it with a set of coefficients, and finally a C2C inverse FFT is applied to complete the calculations. With such scheme, a 30% of efficiency has been achieved. In the end, we demonstrate the accuracy and efficiency on a seismic imaging project.
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Viscoelastic Forward and Adjoint Modeling with OpenCL on Heterogeneous Clusters
Authors G. Fabien-Ouellet, E. Gloaguen and B. GirouxSummaryEfficient seismic modeling is more and more needed because of the advent of full waveform inversion (FWI). For real case FWI, an efficient usage of the available computer resources is paramount. With the diversity of processor architectures found today, this is not a trivial task. In this study, we investigate the use of OpenCL to take advantage of large heterogeneous clusters in the context of FWI. The main objective is to present a scalable, multi-device code for the resolution of the viscoelastic wave equation that can compute the gradient of the objective function by the adjoint state method. We present several algorithmic aspects of our program in details, with an emphasis on its different levels of parallelism. The performance of the program is shown with several tests performed on large clusters with nodes containing three types of processors: Intel CPUs, NVidia GPUs and Intel Xeon PHI. We obtain a speed-up of more than 80 when using GPUs compared to a single threaded implementation and a linear scaling when computations are divided on separate nodes. Our results show that OpenCL allows a better usage of the computing resources available using a single source code for a multitude of devices.
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A CPU/GPU Heterogeneous Hybrid Parallel Algorithm of Prestack Time Migration in Local Angle-domain
More LessSummaryPrestack time migration (PSTM) in local angle-domain (LAD) prompts more reasonable utilizations of recorded seismic data but consumes massive amounts of memory and long computing time. To fully use the computing resource and to improve the computing efficiency, a central processing unit (CPU) and graphic processing unit (GPU) heterogeneous hybrid parallel algorithm of LAD migration is developed on GPU cluster. This algorithm realizes distributed computing on different platforms successfully and contains both GPU algorithm and CPU algorithm of LAD migration. It not only uses GPUs but also utilizes CPU cores to share the computing tasks. First, a new seismic data division method is proposed to reasonably divide large-scale data among CPU cores and GPUs. Second, a new Message Passing Interface (MPI) and Compute Unified Device Architecture (CUDA) pattern is presented to call CPU cores and GPUs at the same time. Third, the CPU/GPU heterogeneous hybrid parallel algorithm is developed and is applied into the actual data. Results demonstrate that our algorithm has the same migration profiles with the CPU algorithm and high accelerating performance. The computing time of our algorithm is the shortest, which is 235 times shorter than 20 4-core CPUs and 1.7 times shorter than that of 4GPUs.
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Exploring the Use of SPIKE-based Solvers on Large Electromagnetic Modeling
Authors S. Rodriguez Bernabeu, V. Puzyrev, M. Hanzich and S. FernándezSummaryFrequency-domain seismic and electromagnetic modeling requires solving the linear systems resulting from the discretization of the corresponding time-harmonic equations. Geophysical inversion is typically performed using several discrete frequencies and multiple (up to tens of thousands) source/receiver combinations. Limitations of classical direct and iterative sparse linear solvers have caused the development of the so-called hybrid methods that can be viewed as an intermediate approach between the direct and iterative methods. We present an efficient parallel solver based on the SPIKE algorithm. Several examples in frequency domain electromagnetic modeling illustrate the computational efficiency of the developed method in terms of memory demand and floating-point operations. Multiple sources can be efficiently handled by employing sparse direct solvers in the factorization of diagonal blocks of the system matrix. Based on the divide and conquer idea, this kind of algorithms exposes different parallelism levels, being suitable to take advantage of multiple accelerator devices. The SPIKE solver partially overcomes the fill-in problem of direct solvers, allowing to solve much larger domains on the same system.
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GPU Accelerations on the 3D Elastic RTM Method
More LessSummaryAs one of the important migration methods, reverse time migration (RTM) generally accounts for a large part of the computing time. In recent decades, the desire for covering larger region and acquiring better resolution has greatly increased the algorithmic complexity of RTM. Therefore, computing platforms and optimizing methods that can better meet such challenges in seismic applications become great demands. This work focuses on accelerating the 10th-order stencil kernels from an elastic RTM algorithm by using the Nvidia GPUs. We first modify the backward process in the matrix format by adding extra layers, to generate a straightforward stencil kernel. A set of optimizing techniques including memory and computing approaches is then performed to design the RTM stencil on the K40 GPU. By further using the the streaming mechanism, we manage to obtain an communication-computation overlapping among multiple GPUs. The best performance employing four K40 GPU cards is 28 times better over an OpenMP version based on a socket with two E5-2697 CPUs.
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Intel Xeon Optimizations for Elastic Wave Propagators
Authors A. Farres and M. HanzichSummaryIn order to cope with the huge amount of computational resources need by an elastic, anisotropic, wave propagation engine, optimizations must be done taking into account the architecture where it runs. We will show strategies evaluated and applied to an elastic propagator based on a Fully Staggered Grid, running on the Intel R Xeon family processors. The evaluated set of optimizations ranges from memory to compute optimizations. Our results show that it is possible to obtain a total speed-up of 4 on this architecture.
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High Performance GPGPU Structure-preserving Smoothing for Seismic Amplitude Data by Anisotropic Diffusion
Authors G.M. Faustino, P.C. Pampanelli, J.M.V. Duarte Junior, E.A. Perez, E.R. Silva, P. Frederick and P.M.C. SilvaSummaryNoise attenuation plays an important role in seismic data processing and interpretation. In recent years, the anisotropic diffusion filter has received much attention since it has superior performance in edge-preserving while smoothing noise from noisy signals. This work presents a high-performance General Purpose Graphics Processing Unit (GPGPU) structure-preserving smoothing for seismic amplitude data by anisotropic diffusion. The obtained results show that the proposed method runs in iterative time, and is able to remove noise and preserves structural features efficiently. We also compare the computational performance of CPU and GPU implementations and show that GPU is about 14 times faster.
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The Parallel Forward Modeling of the Wave Equation Based on AVX Instruction Set
More LessSummaryThis paper describes the parallel simulation of the memory/computing-intensive and large-scale three-dimensional acoustic wave equation with CPU stencil optimization. Taking the 8-core shared storage platform as an example, we obtain a one-time speed-up ratio of 6.7× compared with the serial program by using a coarse-grained OpenMP parallel scheme. Our method vectorizes the data on the template buffer with Single Instruction-Multiple Data techniques to further exploit the computing potential of the CPUs. We apply an 8-channel parallel vector to simulate seismic wave fields with the 256-bit AVX instruction set. This increases the computing bandwidth, thereby eliminating a significant volume of computing instructions and ultimately obtaining a secondary speed-up ratio of 3-7×. Finally, we analyze the factors affecting the secondary speed-up effect of AVX through complicated three-dimensional forward modeling experiments using the Salt model. The results indicate that the memory, cache, and register can better cooperate with each other when vectorization is conducted along the shortest direction of the model data cube, and that the speed-up effect can be enhanced by optimizing the AVX algorithm under such a principle.
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Time-lapse Observations from PRM at Snorre
Authors M. Thompson, M. Andersen, S.M. Skogland, C. Courtial and V.B. BiranSummaryThe PRM operation at Snorre, by autumn 2015, had acquired four seismic surveys. It will be demonstrated, though examples, that through PRM it is possible to monitor production effects, with only some months interval between surveys, and that it is further possible to differentiate between a water and gas during a WAG cycle. Additionally it will be shown that the fast turnaround of data allows for speedy feedback on newly completed well operations. The requirements for frequent acquisition and faster turnaround have been achieved by PRM.
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Grane Permanent Reservoir Monitoring - Meeting Expectations!
Authors R.M. Elde, S.S. Roy, C.F. Andersen and T. AndersenSummaryBy August 2014 a full Permanent Reservoir Monitoring system was installed on the seafloor at the Grane field.Thirteen months later, in September 2015, three full field surveys have been acquired.
The requirements for high data quality, frequent acquisition and expected turnaround for acquisition and processing have been retrieved. Preliminary processed data have been delivered few weeks after last shot was acquired. Production effects are observed and confirm the usability and ability of frequently acquire high quality 4D seismic data.
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Seabed Subsidence Monitoring at Snorre with PRM Inclinometer Measurements
Authors M. Houbiers, R. Macault, T. Røste and M. ThompsonSummaryGeophysical reservoir monitoring (GRM) is important for optimizing field management. Along with traditional GRM methods, monitoring of seabed subsidence might provide additional insight in what is going on in the reservoir and the overburden over time, both from a production optimization as well as from a health, safety, and environmental point of view. We propose a method for monitoring seabed subsidence using inclinometer measurements acquired with a PRM system. The method is applied to passive PRM data acquired at Snorre between May and November 2015, resulting in a qualitative map of seabed subsidence. The method requires that the PRM sensors only move due to subsidence. However, the Snorre PRM system is installed in 2013-2014 and natural backfill of the trenches is expected to be ongoing for some time after the sensors are deployed in the seabed. Yet we believe that the method can be used for monitoring seabed subsidence when the sensors have stabilized, and inclination measurements are acquired frequently and regularly over time.
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A New Method for Field-wide Real-time Subsidence Monitoring with Sub-centimeter Accuracy
Authors H. Ruiz, R. Agersborg, B. Fagerås, L.T. Hille, M. Lien, J. E. Lindgård and M. VatshelleSummarySeafloor subsidence is an observable effect of reservoir compaction, and hence provides important information for the management of offshore reservoirs. In some extreme cases, seafloor subsidence can compromise the safety of the installations and even cause well failure.
This abstract proposes a new, patented system for real-time monitoring of subsidence over large areas with sub-cm accuracy. The system consists of two main elements. The first is a grid of pressure sensors permanently deployed on the seafloor. The sensors can be integrated in a full-scale permanent reservoir monitoring system or a smaller caprock integrity monitoring system.
The second element is a periodical surveying that provides the calibration of the seafloor sensors, by means of the comparison of the real-time seafloor measurements with the subsidence measured between the baseline and the repeat surveys.
This abstract describes first the method used for the periodical surveying, traditionally used for measuring both 4D gravity and subsidence. Then, the challenges related with the integration of pressure sensors in a permanent monitoring system at the seafloor are introduced, and the need for an in-situ correction for the drift of the sensors is motivated. The new method for solving this problem is described in the last section.
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CO2 Reservoir Monitoring Using a Permanent Electrode Array - The Ketzin Case Study
Authors C. M. Schmidt-Hattenberger, D. Rippe, T. Labitzke, P. Bergmann and F.M. WagnerSummaryAt the Ketzin pilot site (Germany), a permanent downhole electrode array is accompanying the geological CO2 storage operation from June 2007 until December 2016. Electrical resistivity tomography (ERT) results provide images about relevant operational stages of the storage reservoir. The presented geoelectrical downhole system displays a very promising long-term behavior, and its technical effort and cost has been amortized by its continuous application during the complete injection history. The experiences drawn from the Ketzin site yield strong arguments for the application of the ERT method as part of a multi-disciplinary monitoring concept.
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The CO2CRC Otway Project deployment of a Distributed Acoustic Sensing Network Coupled with Permanent Rotary Sources
Authors B.M. Freifeld, R. Pevzner, S. Dou, J. Correa, T.M. Daley, M. Robertson, K. Tertyshnikov, T. Wood, J. Ajo-Franklin, M. Urosevic and B. GurevichSummaryWe have deployed a novel permanent monitoring system at the Australian CO2CRC Otway Site that includes a surface and borehole distributed acoustic sensing (DAS) network with orbital vibrator (rotary) surface seismic sources. DAS is an emerging technology for performing seismic acquisition based on optical interferometric techniques, which allows for data collection with a wide spatial aperture and high temporal resolution using commercially available telecommunications fibres. DAS sensitivity currently lags behind conventional discrete geophone and hydrophone sensor technologies. Our implementation of surface rotary seismic sources is based on open-loop controlled asynchronous motors. This avoids the complexity of feedback loops for phase control, instead using deconvolution of the source function as measured by a shallow source-monitor sensor. Initial data analysis shows that the amount of energy available from long source sweeps overcomes limitations in DAS sensitivity. The combination of relatively inexpensive but powerful permanent surface sources with permanent DAS deployment in an areal array provides a new paradigm for time-lapse seismic monitoring. The methodology we describe has broad applicability for long-term reservoir surveillance, with time-lapse change sensitive to many subsurface properties.
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Correlating Frequent InSAR Deformations with Reservoir Pressure for Areal Conformance in Thermal EOR at Peace River
Authors C. Didraga and J.L. LopezSummaryWe present a preliminary analysis of the InSAR data acquired over the Pad 31 thermal EOR development area, located in the Peace River Oil Sands, Alberta, Canada.
While InSAR is often viewed as a technology for reservoir containment monitoring, we demonstrate that it may be very effectively used for conformance monitoring if data are acquired frequently.
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How Permanent DTS Installation Could Improve Well and Reservoir Knowledge
Authors AL Leone and G.G. GALLISummaryThe paper describes, by means of real and blind example, how the continuous thermal profiling provided by permanent DTS is useful for many extra application than the pure fluid allocation purposes. For an unconventional reservoir a permanent and continuous monitoring tool represents the key point to provide a correct management of the reservoir and hence to maximize the recovery factor of the field. The proposed case is based on a horizontal producer drilled in gas shale located in North America. In order to evaluate which are the possible issues that could affect the overall monitoring system, DTS analysis already started before the production phase, directly during the installation. This was the occasion to test and bring the technology to the next step: a proper analysis of the data taken during installation provides additional informations about wellbore conditions whereas the warmback dataset, that followed frack job, increased knowledge about the dynamic attitude of the fractures just created, providing a qualitative forecast about the expected production profile. The final result is that the continuous update in temperature profiling given by DTS could improve significantly well efficiency knowledge and the reservoir performances evaluation even when no further investigations are feasible in the wellbore.
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4D Using Non-repeated OBS Acquisition Systems on the Njord Field
Authors M.S. Guttormsen, S. Ng, Ø.H. Solbu, H. Westerdahl, J. Oukili and T. HøySummarySeismic monitoring has been challenging on the Njord field. The rather weak 4D responses related to production have been difficult to detect due to the noise level in the streamer 4D seismic data and due to dominant overpressure effect after injection. The streamer seismic data was replaced by Ocean Bottom Seismic (OBS) in 2010 and the first repeat was performed in 2014. The 4D noise level is expected to improve using Ocean Bottom Seismic (OBS) due to repeated receiver positions and better coverage closer to installations. However the sensor technologies and the seismic source were not repeated and we show how we accommodated for this. In addition, we will show how the lack of shallow overburden illumination through the OBS acquisition was compensated for using streamer seismic data and imaging with multiples.
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Angle-dependent Water Column Statics Correction through Sparse TauP Inversion
Authors R. Huang, P. Wang, K. Nimsaila and M. VuSummaryWater column statics caused by tidal variation and water velocity change during seismic surveys is one major source of noise in marine 4D projects. Correction of this statics effect is a key step in any marine 4D processing. Applying water column statics correction requires a good knowledge of the distance or surface take-off angle when waves travel through the water column, which conventional methods such as ray tracing are not able to obtain accurately when the subsurface velocity is complex.
We propose a new method to apply water column statics correction through progressive sparse TauP inversion. This method does not need prior inputs of subsurface velocity and reflector dips, as required for ray-tracing methods, and benefits from the progressive sparse TauP inversion engine that can properly handle spatially aliased marine seismic data and mitigate energy leakage in the TauP domain.
We demonstrate the effectiveness of this new method using synthetic ocean bottom seismometer (OBS) data derived from a SEAM velocity model and using real OBS data from 4D surveys over the Atlantis field in the Green Canyon area of the Gulf of Mexico (GOM).
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Simultaneous Time-lapse Imaging via Joint Migration and Inversion
Authors S. Qu and D.J. VerschuurSummaryWe propose a simultaneous Joint Migration and Inversion (SJMI) method for time-lapse migration/ inversion, which combines a joint time-lapse data processing strategy with the Joint Migration and Inversion (JMI) method, and also extend it to include an L1-norm sparsity constraint on the reflectivity model-difference in a suitable transform domain and a total-variation (TV) edge-preserving constraint on the velocity model-difference. We tested the proposed method with two synthetic examples, from which it is shown that our method is effective, even when the datasets contain strong noise, are generated by different acquisitions, and also contain a strongly scattering overburden.
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Time-lapse Repeatability Evaluation of a Multimeasurement Towed-streamer System - A North Sea Case Study
Authors C. Ocampo, P.A. Watterson, C. Cunnell, L. Hodgson and D. DaviesSummaryWe present a case study comprising a time-lapse seismic (4D) repeatability test in the North Sea using a broadband multimeasurement towed-streamer acquisition system. Repeat acquisition with unchanged parameters and minimal time-lapse enabled various wavefield separation techniques to be evaluated, additionally providing a rigorous test for 3D capabilities. Wavefield separation approaches comprised both dual-sensor (PZ) and full multimeasurement (PZY) approaches. The results show consistently higher spatial resolution in the multimeasurement prestack depth migrated volumes, particularly in the shallow section, but also slightly elevated noise levels, especially in the higher-frequency bands. The 4D difference plots are consistent with respect to the elevated noise, but higher 4D signal leakage is observed on the dual-sensor (PZ) data, also within the main signal bandwidth at the reservoir level. This demonstrates a subtle but consistent uplift in the full multimeasurement data set, extending from shallow to reservoir level, suggesting that processing steps including multiple attenuation and migration benefit from dense spatial sampling, even at depth.
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4D Feasibility Case Study in a Mature Oilfield
More LessSummaryFeasibility study is an essential component for 4D seismic projects. It includes rock physics modelling, seismic forward modelling, 4D difference calculation and feasibility study. Among them, rock physics modelling is very important because it links the attributes of reservoir fluid-flow simulation model with elastic properties such as P-wave and S-wave properties, and the measured data of cores in the laboratory are required. However, these data are lack of for some oilfields. But well logging data are available. We propose a method of rock physics modelling using well logging data, based on which 4D feasibility is carried out. It is applied to a mature oilfield where a seismic survey was shot more than ten years ago, which is different from what we usually do, to an undeveloped oilfield. The subsequent 4D case study proves the proposed method is practical, and it is the first 4D project offshore in China.
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A Regularization Algorithm Optimized for Time-lapse Processing
Authors A. Khalil, H. Hoeber, B. Deschizeaux, M. Ibram and D. DaviesSummaryIn time-lapse processing, independent regularization of each vintage is the typical approach. This disregards any geometrical limitations imposed by different surveys. Here we recast the regularization process as a minimization problem with model-space constraints. These constraints couple geometrical relations between surveys to improve repeatability. We also demonstrate how to solve the minimization problem using a practical and pragmatic approach. Results from a North Sea dataset show overall reduction of 4D noise, especially around less repeatable parts of the surveys including the undershoot zone.
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A Novel Approach for Cost Effective PRM Seismic Operations at Snorre
Authors M. Thompson, A.S. Pedersen, M. Andersen and S.M. SkoglandSummaryThe Snorre Permanent Reservoir Monitoring system has a receiver area encompassing approximately 200 km2, and aims to monitor, seismically, the reservoir twice a year; through autumn and spring seismic campaigns. In order to acquire two seismic surveys during a single seismic season in the North Sea, while still maintaining enough separation in time to allow for monitoring of the production effects in the reservoir requires consideration of a novel technique to ensure that both surveys are effectively acquired. Since the seismic sensors are stable from one survey to another, and in the case of no production effects outside the receiver area, shots from outside the receiver area can be borrowed from earlier surveys and used to pad out the repeated surveys during the processing of the seismic. This enables a managed reduction in the annual source effort, while ensuring good time-lapse data quality, and contributes to acquisition of two monitoring surveys per year.
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Measurement and Dynamic Wavefield Correction for Time-dependent Water-velocity Changes
Authors R. Zietal and R.R. HaackeSummaryChanges in water velocity produce significant 4D noise in time-lapse images. To be addressed accurately, the water-velocity problem requires two major ingredients: 1) water velocity must be estimated accurately at all acquisition times and for all shot/receiver locations, 2) time-variable corrections to the data must be dynamic to treat the full wavefield accurately. We present a new approach to parameterization of water-velocity changes which minimizes sensitivity to water depth, allowing data redundancy to be exploited to increase robustness and precision of water velocity estimation. Dynamic correction of the wavefield is then achieved by designing 3D time-variable phase-shift operators that extrapolate data through the water column with a time-variable water velocity and re-extrapolate back to the acquisition datum with a stationary (reference) velocity. This is applied in a tau-px-py least-squares modeling process. Application of the method to deep-water OBN data shows significant improvements in data repeatability, decreasing 4D noise and increasing focus and clarity of the 4D signal.
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High Resolution Model Building and Broadband Imaging in Deep Water Offshore Angola
Authors A.A. Shmelev, A. Cooke, O. Zdraveva and J. PenwardenSummaryWith increased interest in pre-salt hydrocarbon exploration in Kwanza Basin offshore Angola, reliable and accurate information from surface seismic data is critical to successful imaging. This area, however, presents many challenges to the geophysicist, being characterized by complex salt geometry, high velocity carbonate layers, a faulted tertiary section and limited well control. In such an environment the desired seismic would have long offsets, rich azimuthal coverage and be broadband by design. Using the latest data-processing techniques, including deghosting and high-resolution model building, a combination of reflection tomography and full-waveform inversion (FWI) we add significant value to existing, conventionally acquired, narrow-azimuth datasets, ultimately leading to improved imaging and interpretation confidence in pre-salt structures.
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Full Waveform Inversion and Ambiguities Related to Strong Anisotropy in Exploration Areas – Case Study Barents Sea
Authors Ø. Korsmo, S. Marinets, S. Naumann and G. RønholtSummaryIn this case study from the Barents Sea, we have used refraction based Full Waveform Inversion (FWI) in an extreme anisotropy regime without the support from well information. We reveal our observations for decoupling the vertical and horizontal velocity, which enables us to achieve good data matching as well as flat gathers, focused images and a geological consistent model. Our frequency cascaded FWI flow results in a high resolution velocity model to the depth of interest, following the faulted crest in great detail, as well as low velocity zones correlating with the bright spots in the seismic image.
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TI Anisotropy Calibration with Sonic and Walkaway VSP
Authors R. Guerra, E. Wielemaker, F. Miranda, M. Ferla, F. Pampuri, S. Gemelli and V. MattonelliSummaryVelocity anisotropy calibration using Walkaway VSPs or sonic data has been shown to deliver net quality improvements in seismic imaging. Nevertheless, common industry workflows still do not take full advantage of all available data. In this study, advanced borehole sonic and Walkaway VSP data acquired in a single presalt vertical well were combined to estimate continuous depth profiles of Thomsen parameters. These parameters were successfully propagated away from the well in the surface seismic velocity model, in order to minimize the Walkaway transit time residuals.
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RTM Imaging Conditions and Image Enhancement via Optical Stacking
Authors I.F. Jones, M. Kobylarski and J. BrittanSummaryThe final stage of a migration process is usually the imaging condition, which brings together elements of the upcoming and downgoing wavefields for each shot gather in order to form an image contribution. This procedure suffers limitations due to the approximations made in representing the physics of the system, but in addition to that, the final summation of all shot contributions necessarily assumes that the subsurface parameter model was perfect, such that all image contributions align perfectly for summation (within a Fresnel zone), as well as having recorded data that are noise free and adequately sampled. In this work, we assess the effect of unresolvable velocity errors on the final image, and present a case study example of a technique for compensating for these errors via techniques borrowed from astronomical image processing applied to each of each of the many thousands of elemental traces that contribute to the final image.
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Integrating Geophysical and Geological Models for De-risking Hydrocarbon Exploration – a Rio del Rey Basin Case Study
Authors P.G. Wilson, J. Wanstall, M.P. Jameson, M. Nuzzo, P. Nguema and S. TamfuSummaryThis paper presents a case study outlining key technical developments and the integration of geophysical and geological models that have advanced our understanding of the hydrocarbon plumbing in the Agbada Formation in the Rio del Rey Basin, offshore Cameroon. Geophysical techniques including extended elastic impedance and seismic fluid classification were developed using elastic log data and modern 3D seismic data. These techniques were shown through the drilling of the Oak wells to aid the prediction of presence and hydrocarbon phase in exploration targets. Gas composition analysis in the wells combined with seismic interpretation has resulted in an understanding of how the different oil and gas reservoirs have been sourced. Integrating the geophysical and geological models means there is a coherent approach to de-risk the presence and phase of hydrocarbons in the prospects.
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A Successful Geophysical Prediction of Fractured Porous Basement Reservoir - Rolvsnes Oil Discovery 2015, Utsira High
Authors J.E. Lie, E.H. Nilsen, E. Grandal, K. Grue and R. SørlieSummaryThe Southern Utsira High in the Norwegian North Sea was explored on and off for more than 40 years before Lundin Norway made the Edvard Grieg breakthrough discovery in 2007 (186 million bbls of recoverable oil). This discovery opened up for the giant Johan Sverdrup 16/2-6 discovery in 2010 (reserve range of 1,7-3,0 billion bbl of oil). Triassic to Cretaceous clastic sandstones are here the main reservoirs.
The most recent oil discovery on the Southern Utsira High was made by the 16/1-25 S, Rolvsnes, well. This well targeted and found oil in fractured porous granitic basement. In this paper, Lundin Norway will present this basement discovery and the geophysical methods used to distinguish between tight and fractured/porous basement which allowed for a successful placement of the Rolvsnes well.
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De-risking Drill Decisions - A Case Study on the Benefit of Re-processing Conventionally Acquired Seismic data
Authors E. Knight, J. Raffle, S. Davies, H. Sherazi-Selby, E. Evans, M. Johnson and I.F. JonesSummaryAcquiring and processing a new vintage of seismic data can often fall outside the time frame of ongoing field development, In this case, careful and detailed reprocessing of vintage seismic data can be a practical and timely way of de-risking any imminent drilling decisions.
Here we consider one such case study over the Thistle field, in the Northern Sector of the North Sea, demonstrating how contemporary de-ghosting of conventional marine streamer data, combined with refined demultiple techniques and iterative non-parametric tomographic preSDM model building facilitate more reliable well-track planning.
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Infill Opportunities after 45 Years of Production from the L10 Central Gas Field, Dutch Sector of the Souther North Sea
Authors G. Daniau, J. Guyomard, H. de Haan and T. BenedictusSummaryIn 1969 the Placid Oil company made the first offshore gas discovery in the L10 block of the Dutch sector of the Southern North Sea. The asset now operated by ENGIE is producing gas from the Permian Rotliegend sandstone reservoir, located at a depth of about 4000m. After 40 years of production, ENGIE decided to acquire a new Pre Stack Depth migrated seismic. The aim was to benefit from a large continuous seismic dataset and apply the latest processing technology in order to unlock remaining potential of this asset. It was the starting point of a complete data review going from structural geology (field compartmentalization and fault seal analysis), to sedimentology (core description, well correlation), petrophysics (homogenize decades of well logs interpretations) and production data (formation pretest and material balance analysis). This work has resulted in de-risking several prospects and identifying new infill opportunities. The example of the L10 Central field review will illustrate this successful story.
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Reservoir Architecture Modelling for Geothermal Energy Production - Case Study of the Delft Sandstone Member, West Netherlands
More LessSummaryDeep-geothermal energy projects operate with a geothermal doublet comprising a hot-water produc-tion well and a cooled-down water injection well. Both wells target the same aquifer to maintain pressure support in the reservoir. The injection well ends at shallower depth than the production well to allow for gravity-driven cold-water front propagation. These conditions determine the doublet layout. A detailed knowledge of reservoir architecture and connectivity in the aquifer is required to assess the pressure communication between the wells, and to reduce the economic risk of these projects. A case study for a planned geothermal doublet research project in the Delft Sandstone Member (Valanginian, West Netherlands Basin) shows that the target comprises stacked sandstone interbedded with mudstone and lignite. Core, cutting, well-log and seismic analyses show that the sandstone formed by meandering rivers in a SE-NW elongated rift basin. The reservoir is subdivided in three units on the basis of variations in net-to-gross, log signature, lithofacies interpretation and stacking density. Unit 3 the best porosity and permeability values, is sand-prone and characterized by multi-storey and laterally-amalgamated meandering river sandstone bodies with minor mudstone floodplain intervals. Optimal placement of geothermal doublet is in the NW-SE trend of the fluvial pathway.
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Comparison of the Petrography and Petrophysical Parameters of Fontainebleau Sandstone - Measurements and Literature
Authors F.S Al Saadi, K.H. Wolf and C.K. KruijsdijkSummaryCharacterizing and understanding porous media is essential prior to standardized core-flow experiments, to investigate oil mobilization on a single-mineral porous medium with a limited permeability/porosity band width, and a homogenous pore- and grain-framework. Literature shows that one almost pure quartz horizon in the Fontainebleau sandstone meet these preconditions. Fresh samples were gathered from the “Gres de Fontainebleu and Cie” Quarry. Knowing the depositional environment and burial history, we measured and quantified spatial attributes of the matrix by CTS image analysis, associated stereological measurements, statistical 2D/3D reconstructions and petrophysical laboratory measurements. Permeability, porosity, capillarity, specific surface, pore framework and pore coordination number distribution were measured and compared with literature. This new database provides a comprehensive review on the Fontainebleau sandstone from micro-scale to meter scale for a porosity bandwidth of 0.05 - 0.11 and permeability bandwidth of 10 - 400 mD. The combined measurements, petrophysical and spatial properties support, are used for prediction, modeling and interpretation of comparative core-flow experiments meant for oil mobilization by chemical injections (surfactant & solvent), i.e. chemo-physical interaction of rock/fluids and multi-phase fluid/fluid adsorptions. Similarly, mapping the pore framework helps modelling the mobilization and transport of the oil from mm-scale to m-scale.
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Reservoir Quality within the Johan Castberg (Formerly Skrugard) Field in the South-Western Barents Sea
More LessSummaryThe Johan Castberg Field is located on the western margin of Loppa High in the south-western Barents Sea and comprises a reservoir in Lower-Middle Jurassic sandstones of Stø and Nordmela formations containing both oil and gas. Cored intervals, 15 samples (well 7220/5-1) and wells log data (7219/8-1, 7219/9-1, 7220/8-1 and 7220/7-1) have been used for petrophysical and petrographical study of sandstone reservoirs. Reservoir properties are preserved significantly due to uplifting and erosion of the entire region. Sandstone diagenesis is a function of burial rate, mineralogical composition and texture, climate, and hydrodynamic and geothermal gradients.
X-ray diffraction (XRD), Optical Microscopy, Scanning Electron Microscopy (SEM) and Core logging have been performed to investigate the depositional environment, clay mineralogy, role of sediments composition, facies distribution, and provenance of the reservoir sandstones. Petrographical study has been carried out to find the diagenetic clay and microquartz coatings, quartz cementation and its distribution in the sandstone reservoirs.
Lower-Middle Jurassic sandstones are moderate to well sorted, fine to medium grained and are mineralogical mature. Sandstones are deposited in prograding coastal regime whereas shale interval indicates regional transgressive pulses during deposition. The porosity and IGV values of sandstones range 6–26% and 25–34% respectively. The porosity is still well preserved and reservoir quality of Lower-Middle Jurassic sandstones in well 7220/5-1 is very good.
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Characterization of Microscopic Pore Structure and its Effect on Macroscopic Physical Parameters in Tight Gas Reservoirs
Authors L.C. Zhang, S.F. Lu and D.S. XiaoSummaryA combination of mercury intrusion capillary pressure (MICP) and N adsorption experiments were performed on tight rock samples from the Shahezi formation in Xujiaweizi Default Depression in order to detect the applicability of the two techniques for characterizing the complete pore size distribution and gaining insight into the microscopic pore structure and its effect on macroscopic physical parameters. N adsorption and MICP measurements were used to analyze the pore size distribution of mesopores and macropores respectively. The result shows that tight gas reservoirs are characterized by complicated microscopic pore structure with a broad pore size distribution from 2nm to 200μm. The dominant pores range from 10nm to 2μm, which mainly consist of slit-shaped pores and ink-bottle shaped pores. Porosity, permeability and free fluid saturation decrease with the increase of the volume proportion of small pores (diameter< 50nm), and increase with the increase of the volume proportion of large pores (diameter>200nm). Furthermore, the relationship between the volume proportion of different pores and permeability and free fluid saturation is better than that with the porosity.
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New Insights on the Characterisation of the Pyroclastic-rich Bajo Barreal Fluvial Reservoir (Argentina)
SummaryThe Cretaceous fluvio-lacustrine Bajo Barreal Formation, known for its large hydrocarbon accumulations, consists of a 1) Lower Member made of floodplain mudstones with isolated channels with an upward increase of sandstone content, and an 2)Upper Member composed by grey and purple mudstones with thicker channel sand bodies. Both stratigraphical units are characterised by the presence of acid volcanoclastics and tuffaceous material mixed with siliciclastic sediments. Previous studies on the Bajo Barreal Formation suggest an active sedimentary input from contemporaneous volcanoclastic material derived from both direct fall-outs or rain-off processes. This material can make up to 15% of host rocks forming a so-called pseudomatrix produced by the disintegration of tuff and d pyroclastic material. In this contribution we present the preliminary results on the reservoir petrography and mineralogy focusing on the characterisation of its volcanic component and related neo-formed mineralization especially considering the clay and zeolite pore infill. The identification of key petrographically distinct stratigraphic units and the detailed quantification of their mineralogical composition (i.e. clay and zeolite content) has an important impact on characterisation of pore-filling material, porosity calculation from density-based wire-line log and the stratigraphic distribution of reservoir properties and hence definition of flow units.
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Relationship between Rock Typing and Petrography - A Case Study on the Fahliyan Formation in the Persian Gulf
Authors M. Goodarzi, M. Jamalian, D. Amirsardari, M. Jamalian and J. ShoghiSummaryThe Lower Cretaceous Fahliyan Formation in the Persian Gulf was the subject of this study. The main target of the study is investigation of relationship between different rock types and sedimentology study. In order to define rock types based on porosity-permeability data, hydraulic flow units were investigated based on Flow Zone Indicators (FZI). As a result, six hydraulic flow units were recognized in the Fahliyan Formation of the studied area. Moreover, productive intervals of the reservoir were identified using Normalized Cumulative Reservoir Quality Index (NCRQI).
Assessment of porosity and permeability data indicates that microfacies pertaining to shoal and channel facies belts with grain-supported texture have the best reservoir quality. This is due to abundance of interparticle porosity. These facies belts correspond with HFU-4, 5, and 6. According to Winland plot, the mentioned HFUs are comparable with macroport and megaport classes. Microfacies of tidal flat facies belt also have good reservoir quality due to fenestra porosity. Microporosity is dominant in most facies of the studied samples. The samples with microporosity pore type (such as most of the microfacies belong to shallow open marine and lagoon facies belts) do not have enough permeability to make a good reservoir zone.
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Reservoir Characterization of Giant Gas Condensate Bearing Kangan and Dalan Formations
By S. DowlatiSummaryKangan and Dalan formations are a permo-triasic basin in the Persian Gulf Region which contains four lean-condensate gas bearing reservoir units named as K1, K2, K3, and K4 from top to bottom. These formations, outstretched in a vast area of Persian Gulf region, embedded gigantic reserves of gas condensate mainly deposited in Iran, Qatar, Saudi Arabia, Bahrain, and Abu Dhabi. Kangan/Dalan formations are synonymously called Khuff formation in southern countries of the Region, while in this paper Iranian part of the formations is studied.The purpose of this paper is to characterize reservoir properties of these four layers based on their well logs, special core analysis, rock typing methods, and PVT lab data. So a comprehensive approach applied to correlate porosity, permeability, capillary pressure, mineralogy, and rock typing of these layers and divide them into sub-layers to develop reservoir geological model.
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Geomechanically Calibrated Rock Physics Modelling for 4D Seismic Response Prediction
Authors M. Paydayesh and A. ShamsaSummaryDisturbing reservoir equilibrium by production or injection causes changes in saturation, pressure, and temperature, hence, substantial alterations on the stress state of a reservoir. In addition to vertical p-wave and s-wave velocity changes, the anisotropy parameters vary during production activities due to both pore pressure and saturation change. The anisotropic nature of stress-induced velocity change must be considered in 4D seismic analysis. Therefore, coupling fluid substitution with geomechanical modelling as demonstrated need to be considered. This work addresses the integrated modelling of 4D seismic response and how geomechanical stress direction calculation can be embedded in the petro-elastic modelling and fluid substitution.
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Structural Parameters Effect on the Sleipner CO2 Underground Storage Simulation History Match
More LessSummarySeismic history matching of the Sleipner CO2 injection simulation is a challenging and ongoing research area. At this paper, capacity of a number of seismic attributes in improving the structural interpretation of the baseline seismic data is demonstrated. In addition, effect of two structural uncertainties, namely, reservoir boundary and structural relief, on the Sleipner simulation history match is addressed. The simulation results illustrate potential of the alternative reservoir boundary on the Sleipner seismic history match improvement.
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