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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 - 20 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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