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79th EAGE Conference and Exhibition 2017
- Conference date: June 12-15, 2017
- Location: Paris, France
- Published: 12 June 2017
1 - 50 of 1073 results
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A New Method for 2D NMR Log Data Inversion in Tight Sandstone Reservoir
More LessSummaryTo improve the inversion effects of 2D NMR log data of the tight sandstone reservoir, this paper applies the two parameters regularization inversion method to the data. The principle of the method is elaborated in detail. The results of applying the method to the simulated 2D NMR log echo data indicate that two parameters regularization inversion method, which can overcome ill-posed nature of 2D NMR log data inversion and obtain a high inversion precision, is much suitable for inversing 2D NMR log data. The inversion results of the 2D NMR log data of tight sandstone reservoir using the two parameters regularization algorithm can be uesed to identify reservoir fluids.
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Estimating Permeability in a Carbonate Reservoir of Campos Basin Combining Well Logs and Multiple Linear Regressions
Authors P. Almeida, A.A. Carrasquilla and A. CarrasquillaSummaryFrom the data set of two wells drilled in a carbonate reservoir in Campos Basin - Southeastern Brazil, this article made the estimation of permeability using geophysical well logs in conjunction with the multiple linear regression technique. The main difficulty to characterize this type of reservoirs consists in that the carbonates have a broad variance in their physical attributes. For this understanding, it was then projected to separate the reservoir into zones according to their different petrophysical features. So, based on gamma rays, resistivity, density, neutronic and sonic logs, certain parameters of the reservoir such as irreducible water saturation, top and bottom of the reservoir, oil/water contact, porosity and oil-producing areas were determined. In addition, geological attributes were applied to validate qualitatively the study, when the reservoir was divided into zones in conformity with the environment energy at the time of deposition of the deposits. In the final, the estimate showed good fit with the permeability measurements in the laboratory through of this simple and fast method.
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Integrated Visualization of Subsurface Appraisal and Field Development Plan - A Key Input to Support Post Discovery Capital Intensive Investment Decisions
Authors H. Stigliano, I. Yemez and V. SinghSummaryAfter a field discovery, E&P companies spend billions of dollars every year for subsurface appraisal. Most often, the appraisal decision is difficult and tortuous, lacks transparency and objectivity, and the level of appraisal is less than optimal which affect the full cycle project economics. This paper is an effort to manage uncertainty through appraisal by quantifying its impact on the field development plan and overall project profitability. An integrated approach of selecting appraisal well location and their sequencing using standard discounted cashflow analysis was adopted to calculate commercial value of a project in terms of an economic indicator considering different uncertain variables, their dependencies and correlation between them. To quantify the specific appraisal activity benefits, in terms of uncertainty reduction and its economic reward to the field development plan for an offshore clastic reservoir discovery, the Value of Information approach along with decision tree analysis was used and a comparison between different evaluated scenarios was made for an optimal appraisal selection. This method has helped prioritizing the appraisal locations including their sequencing, ensuring that appraisal plan adds value and allows management to understand the post discovery risks/opportunities for future investments.
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Faster reservoir simulation allows multi-million cells models: are fine grids requiring fine reservoir geologist?
Authors F. Bigoni, A. Francesconi, V. Tarantini and R. MarinoSummaryIn the last years, the better performance of computational centers and the more powerful software allow the building of 3D reservoir models with higher number of active cells and the use of the fine geological static model to make dynamic simulations.
In the past, reservoir geologists experienced some frustration when their detailed 3D fine grid geological description resulted almost obliterated by the upscaling processes. Given the new context, geologists can drop their discomfort for the upscaling smoothing effect and focus on a reservoir description “fit for grid”, which can result much more detailed and closer to the real complexity of the rock.
However, this process is not trivial calling for a much more detailed and sharp geological description. In fact, the upscaling process in some way could mask geological wrong assumptions because they resulted smoothed and mitigated by the upscaling process.
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A Semi-Empirical Model for Interpreting Rock Strain Sensitivity in 4D Seismic Data
Authors C. MacBeth, A. Kudarova, P.J. Hatchell and J. BrainSummarySeveral models have been recently proposed to connect observations of velocity change with strain deformation in and around reservoirs undergoing production and recovery. In this work we show that a simple compliance-based model combined with the original conceptual understanding of Hatchell and Bourne (2005) can adequately explain the magnitude of R factor values currently observed from calibrated field data in a variety of settings. The model is also used to determine an expression for the gradient of overburden time-shift variation with incidence angle. This gradient is predicted to be low but may vary according to the ratio of tangential to normal compliance at the intergranular contacts. This factor could perhaps be used as an additional parameter to assess the post-production state of the overburden.
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Monitoring the Ormen Lange Field with 4D Gravity and Seafloor Subsidence
Authors M. Vatshelle, M. Glegola, M. Lien, T. Noble and H. RuizSummaryThe primary development drilling at the Ormen Lange field at the Norwegian continental shelf concluded in 2014. Reservoir monitoring is employed to reduce subsurface uncertainties and assist with late field-life development decisions. Geophysical methods used include 4D seismic, seafloor geodesy and field-wide 4D gravity and subsidence surveys. This abstract presents the results on both seafloor subsidence and 4D gravity from the surveys performed in 2012 and 2014. These results are provided at a lower cost and significantly faster turnaround compared to 4D seismic.
While 4D seismic does not provide sufficient sensitivity to seafloor subsidence at Ormen Lange because of oceanographic variations, 4D gravity and subsidence surveys provide a clear picture, that is key for understanding and monitoring reservoir compaction.
4D gravity results, in turn, provide a valuable input to understanding mass changes in the reservoir. This input has less lateral resolution than that from 4D seismic, but as gravity is sensitive to mass changes, it provides immediate insight into the energy balance of the field and can be quickly integrated into history matching workflows. The integration of gravity and time-lapse seismic provides a reduction of uncertainties on aquifer influx and strength, with increased confidence through the consistency of independent methods.
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Time-Lapse Seismic Signal in the Overburden of Producing Reservoir - Separating Possible Causes
Authors D. Rappin, Y.-M. Leroy and J. FioreSummary4D time-lapse seismic is a standard technology nowadays to describe reservoir property changes during field production, especially pressure variations and fluid movements. Seismic information does not directly provide these physical properties, but seismic velocity changes or impedance changes can be obtained throughout inversion processes.
In this paper, we present several examples of 4D signature encountered in the overburden of different producing reservoirs, in various geological contexts.
The impact in the overburden of producing reservoir is not straightforward. There are many potential causes separate or combined to explain the observed 4D time-shift. Geomechanical effects became obvious in many cases. Effective displacements, subsidence, fault activation and fracturing, can also have significant local contributions. In addition, fluid evolution in small sandy levels located in the overburden can contribute to the observed 4D time-shift.
Several cases and modeling are analyzed with different complementary workflows in order to separate and determine the weight of contribution of the different causes.
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A Practical Tool for Simultaneous Analysis of 4D Seismic Data, PEM and Simulation Model
Authors A. Briceño, C. MacBeth and M.D. MangriotisSummaryOne of the main focuses of the geoscience industry is to constrain reservoir models to 3D and 4D seismic data using quantitative workflows that are suitable for model updating and history matching. Seismic history matching (SHM) closes the loop and minimizes the misfit between the observed 4D seismic and that predicted by the reservoir model. A key problem in formulating this misfit function is a lack of understanding as to how uncertainties in the seismic data, petroelastic model and simulation model interact. This can lead to lengthy and time consuming workflows. This study presents a simple and interactive way of visualizing these uncertainties whilst optimizing the SHM. The approach is applied initially to a synthetic example, and then to two different field datasets from the UKCS and Norwegian Sea. The results demonstrate that qualitative updates can be successfully applied to the simulation model in the presence of uncertainty in the PEM and noise in the 4D seismic data.
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Wavefield Reconstruction Using a Whole Space Green’s Function Framework
By P. TerenghiSummaryA whole-space Green’s function framework for the representation of the acoustic wavefield is obtained from the Helmholtz wave equation. Under this framework, the wavefield is represented by a distribution of point-sources in space and time, each corresponding to an elementary spherical wavefront.
Intuition suggests the number of equivalent point sources actually required to represent the wavefield of interest might be small compared to the total number of speculative locations. Consequently, in spite of the problem’s innate ill conditioned nature, a satisfying solution can still be obtained by means of sparsity promotion. When a solution is reached, the wavefield can be reconstructed at new or existing locations by utilizing the framework in a forward modelling sense.
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F-xy Domain 2D Mathematical Morphological Filtering for Seismic Data Interpolation
More LessSummarySeismic data interpolation is a currently popular research subject in modern reflection seismology. Compressed sensing (CS) based and rank-reduction based methods have great performances in recovering randomly missing traces, but their assumption or precondition, that traces miss randomly, is too hard to satisfy in real data. In this abstract, we propose a new morphology based method, which utilizes 2D mathematical morphological filtering (MMF) to recover missed energy of each frequency component. Because the morphological calculation is based on logical operation and set theory, which is different from the traditional mathematical transforms, this proposed f-xy domain 2D MMF method has strong anti-aliasing capability. Application of it on synthetic and field seismic data demonstrates a successful performance.
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Simultaneous Reconstruction and Denoising of 5-D Seismic Data Using Damped Sparse Representation Based Projection Onto Convex Sets
More LessSummaryIrregular landform and obstacles result in a irregular field data acquisition. However, the existing seismic data processing methods and techniques are almost based on the assumption and precondition of regularly input data. Besides, the observed seismic data always contains random noise because of impacts from acquisition equipments or the acquisition environment. Thus methods for reconstruction with the presence of noise are necessary. The simultaneous reconstruction and denoising problem can be effectively solved under the theory of compressed sensing (CS), and the projection onto convex sets (POCS) is one of the effective methods to solve the CS problem. In this abstract, we propose a damped sparse representation (DSR) based POCS method. By a introduced damping operator, the DSR based POCS method can obtain a more accurate estimation of signal, namely, a better result of simultaneous reconstruction and denoising. The feasibility of the proposed method is validated via both 5-D synthetic and field data examples.
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A Geometry Dependent Lookup Table Approach to Improve Performance of the OMP Seismic Interpolation Method
Authors Y. Hollander, I. Degani, O. Yilmaz and R. LevySummaryWe present an approach to improve runtime of the \emph{orthogonal matching pursuit} (OMP) method for multidimensional seismic interpolation. OMP is an expansion of \emph{Anti-leakage Fourier Tranfrom} (ALFT) which seeks to further minimize spectral leakage of the computed spatial spectrum. Both methods suffer from low performance efficiency due to the need for iterative computations of forward and backward Fourier transforms. An approach to reduce the necessity of these repeating transform computations was recently presented for the ALFT method. Here we generalize this improvement to OMP, and show a substantial runtime improvement of a factor 4–5 compared to the old approach.
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Mapping of Moveout in Orthorhombic Media
By A. StovasSummaryI define the mapping operator for moveout in tilted 3D medium. The proposed operator is applied for orthorhombic medium with rotation by using 3 Euler angles. It allows to define the kinematic properties in tilted orthorhorhombic medium, and can be used to map any of moveout approximation originally defined for vertical orthorhombic medium.
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Multifocusing Imaging Comparisons Study Based On Cuckoo Search Algorithm
Authors D.Y. Chang, C. Zhang, T. Hu and W. FengSummaryConventional NMO method causes severe stretching distortion. Moreover, for rugged topography data, conventional NMO and stack are based on the elevation static correction, which can be inaccurate because the assumption of vertical ray path is no longer valid. MF method has great advantages because it not only brings no stretching distortion but also can be directly applied without elevation static correction. MF-based stack method can improve SNR on stack section because this method can stack image traces from different CMP gathers. However, the determination of three MF parameters is the most key as well as difficult issue in MF method. In this article, we introduced a new metaheuristic global optimization algorithm, Cuckoo Search (CS), to calculate three parameters. On physical model with rugged topography data, we tested two MF methods, relief surface MF method and implicit spherical MF method. Both methods show better time correction result without elevation static correction than NMO result, while relief surface MF has better time correction than implicit spherical MF because the latter one calculate corrections without considering sources’ and receivers’ elevation.
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Automatic Microseismic Event Detection by Multi-scale Morphology Characteristic Function
Authors Y.Y. Jiang, R.Q. Wang, X.Q. Chen, Y. An and M. ZhangSummaryMicroseismic events detection is a key issue for field real-time microseismic data processing because of the low signal-to-noise ratios. Surface-acquired microseismic events are commonly unpredictable and appear as weak signals, which presents a significant challenge in microseismic data analysis and event detection. A new implementation of the multi-scale morphology characteristic function is proposed for detecting microseismic events automatically. First, the microseismic data are decomposed into different scales by multi-scale morphology decomposition. Then the multi-scale morphology characteristic function is calculated by waveform correlation approach. We have tested the technique on a surface passive seismic monitoring dataset of the microseismic events induced by hydraulic fracturing, and it is proved to be effective by simulation and real data processing. The proposed method has the advantage of suppressing the effect of Gaussian noises and is applicable to the detection of low SNR signal.
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Normalized Set of Global Effective Parameters for Pure-Mode and Converted Waves in Horizontally-layered Triclinic Media
More LessSummaryConsidering reciprocity where the traveltime is an even function of the offset or horizontal-slowness, the fourth-order normal moveout (NMO) series are governed by the normal-incidence time and eight effective parameters: three second-order and five fourth-order. Local effective parameters are related to the individual layers, while the global effective parameters are related to the overburden multi-layer model. Local and global parameters are related by forward and inverse Dix-type transforms. The NMO formulae are different in the slowness and offset domains, but the eight parameters are the same in both cases. We suggest a new set of intuitive normalized effective parameters, classified into two “azimuthally isotropic” and six “azimuthally anisotropic” parameters. We provide feasible ranges for the normalized parameters, thus allowing their used for controlled inversion.
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Scalable numerical modelling patterns for the cloud
Authors J.W.D. Hobro and A. SharmaSummaryThe ready availability of cloud computing resources presents an opportunity for rapid turnaround in large numerical modelling tasks. This opens up new possibilities for interactive modelling in immersive applications. However, it is only feasible for numerical modelling algorithms that scale well over large computing clusters. This is relatively straightforward for algorithms that are embarrassingly parallel, but achieving linear scaling for algorithms such as coupled numerical modelling problems is much more challenging. We explore the improvements that can be achieved in scalability for this type of algorithm by moving away from a sequential programming approach as conventionally used with the Message Passing Interface (MPI), which encourages large-scale synchronisation across a parallel system. Instead we propose an approach based on the actor model that removes all unnecessary synchronisation during inter-node communication. It avoids synchronisation by introducing flexibility in the order of computation. It also spreads communication evenly in time and therefore significantly reduces network contention. We use a theoretical model to examine the scalability characteristics of the new system, which gives improvements of more than an order of magnitude in scalability compared with the sequential approach.
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Finite-difference Seismic Modeling on CPUs/GPUs Using Matrix-vector Products
Authors F. Wittkamp, T. Bohlen and T. SteinwegSummaryModern seismic imaging methods such as reverse time migration (RTM) or full-waveform inversion (FWI) require large high-performance computing (HPC) systems to provide enough computational power to solve a large number of forward problems based on the wave equation. These wavefield simulations are conventionally performed by explicit time-domain finite-difference (FD) methods on regular numerical grids, where the parallelization is often based on a fixed and rather inflexible decomposition of the computational domain. However, such parallelization cannot exploit the computing capacities of modern and especially future exascale HPC architectures, which are expected to become more and more hierarchical and non-uniform. For this purpose, we developed a matrix-vector formulation of the explicit time-domain FD method solving the 3D elastic wave equation. To implement the matrix-vector formalism, we chose the open-source framework LAMA, which allows the development of hardware-independent code. We found that the implementation of such a matrix-vector based 3D elastic forward solver is straightforward. In a strong and weak scaling benchmark, we subsequently explored the scaling behavior of our implementation. The overall scaling performance shows the large potential of our method, which can be improved even further by tuning on the application and framework level.
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Optimizing Fully Anisotropic Elastic Propagation On 2nd Generation Intel Xeon Phi Processors
Authors A. Farres, A. Duran, C. Rosas, M. Hanzich, C. Yount and S. FernándezSummaryThis work shows several optimization strategies evaluated and applied to an elastic wave propagation engine, based on a Fully Staggered Grid, running on the latest Intel Xeon Phi processors, the second generation of the product (code-named Knights Landing). Our fully optimized code shows a speed-up of about 4x when compared with the same algorithm optimized for the previous generation processor.
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Approximating Q Propagations for Elastic Modeling on GPUs
More LessSummaryPropagating wavefields using the explicit finite difference method is the kernel of reverse time migration (RTM) and high-end velocity algorithms in seismic applications. In recent decades there has been a significant increase of interest in the seismic exploration community to invert the image of the subsurface in larger regions and higher resolutions in the elastic media, which brings tremendous computing challenges. As a result, the optimizing methods for improving the performance of the wavefield propagation are in great demands. This work manages to boost the performance of the wavefield propagation in 3D elastic scenarios by approximating the Q propagation and using the multi-GPU platform. We first extend the constant-Q formulation from the 2D viscoelastic case to the 3D viscoelastic case. Different optimization techniques on GPUs are then described for an efficient modeling kernel. We also propose a set of schemes to reduce the computation to further improve the performance. The experimental results show that we can achieve significant performance speedups of 60 to 200 times with 4 GPUs over the CPU-based solution as a function of Q.
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Seismic Facies Classification Using Digital Music Technology and Musical Information Retrieval Approaches
Authors P. Dell’Aversana, A. Amendola, G. Gabbriellini and A.I. MariniSummaryIn this paper, we discuss a novel approach of pattern recognition, clustering and classification of seismic data based on techniques commonly applied in the domain of digital music and Musical Information Retrieval. Our workflow starts with accurate conversion of seismic data from SEGY to Musical Instrument Digital Interface (MIDI) format. Then we extract MIDI features from the converted data. These can be single-valued attributes related to instantaneous frequency and/or to the signal amplitude. Furthermore, we use multi-valued MIDI attributes that have no equivalent in the seismic domain, such as those related to melodic, harmonic and rhythmic patterns in the data. Finally, we apply multiple classification methods based on supervised and unsupervised approaches, with the final objective to classify the data into different seismic facies. We show the benefits of this cross-disciplinary approach through two different applications on two real seismic data sets.
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Airborne EM Modelling for an Anisotropic Earth Using Spectral Element Method
More LessSummaryThough the anisotropy exists popularly in the earth, it is frequently neglected both in geophysical data interpretation and in modelling. However, negligence of the electrical anisotropy can have a serious influence on near-surface prospecting, like airborne electromagnetic (AEM), especially in areas where the underground bears well-developed stratification. In this paper, we first put forward a modelling algorithm, named spectral element method (SEM), for airborne EM modelling for a three-axis anisotropic earth. SEM is a technique based on weighted residual method. The latter uses a polynomial basis function for SEM, which can achieve a high accuracy when increasing the polynomial order. We take as example a horizontal coplanar coil (HCP) of an AEM system to check the accuracy of our algorithm for anisotropic models and we compare the 3rd and 4th order SEM modelling results with 1-D semi-analytical solution for a half-space or layered-earth model. To study the anisotropic effect on AEM responses, we calculate and compare the responses for both isotropic and anisotropic abnormal bodies using 3rd to 5th order SEM. Finally, we analyse the influence of the order of SEM interpolation functions on the AEM responses.
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Fast Simulation of 2.5D LWD Resistivity Tools
Authors A. Rodríguez-Rozas, D. Pardo and C. Torres-VerdínSummaryWe are developing a general one-dimensional (1D), 1.5D, 2D, 2.5D, and 3D Finite Element (FE) library for the fast simulation of borehole resistivity measurements. The library enables to combine problems with different spatial dimensionality and solve them using a single software. As a first step towards the fast inversion of geophysical data, in this work we focus on the rapid simulations of 2.5D logging-while-drilling (LWD) borehole resistivity measurements. Given a commercial logging instrument configuration, we calibrate the FE method offline with respect to (i) the element sizes via non-uniform tensor product grids; (ii) the arbitrary polynomial order of approximation on each element; and (iii) the interpolation of certain Fourier modes. This leads to the design of proper FE discretizations to simulate measurements acquired in an arbitrary 2D formation.Numerical results show that we accurately simulate on a sequential computer any field component at a rate faster than one second per logging position. In parallel, it is expected that the CPU time can be further reduced to below 0.1 seconds per logging position in a modest 128-core for all components of a tri-axial logging instrument. Derivatives (sensitivity functions) needed by gradient-based inverse methods are easily and rapidly computed using an adjoint-based formulation.
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Stress Distribution Around Complex Salt Structures: a New Approach Using Fast 3D Boundary Element Method
Authors L. Maerten, F. Maerten and P. CornardSummaryDuring the last decade geologists and engineers have used the Finite Element Method (FEM) with elasto-plastic or visco-plastic behavior to simulate salt in order to gain a better understanding of the in-situ stress distribution. However, building such FEM models can become time consuming and challenging, especially when complex geometry is involved, and modeling elaborated non-linear salt behavior can take hours to days to process. We have developed a different approach using a fast 3D Boundary Element Method (BEM) and which allows fast model construction and computation (few minutes). Instead of using non-linear mechanical behavior of salt, we use the assumption that salt can be viewed as a pressurized cavity for which unknown parameters like the far field stress and salt pressure gradient are inverted using available fracture, stress or deformation data associated to past or actual deformation around salt. To verify this approach, BEM results have been validated against known 3D analytical solution for pressurized spherical cavity and compared to published, more complex, 3D FEM salt models. The efficiency of this new approach, in terms of model construction and mechanical simulation, is demonstrated through a natural example of faults associated to salt diapirs in the Gulf of Mexico.
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Acoustic VTI Full-waveform Inversion with 3-D Free-surface Topography
Authors M.J. Huiskes, R.-É. Plessix and W.A. MulderSummaryIn land applications, topography may impact the imaging if not taken into account. With low-frequency and wide-aperture data, the long-to-intermediate wavelength components of the velocity model can be recovered by full-waveform inversion. Standard static corrections to handle the topography do not work satisfactorily on long-offset data. We present a method to handle 3-D free-surface topography for acoustic FWI by directly modelling the effect of the topography with an immersed-boundary finite-difference scheme. The numerical scheme is aimed specifically at first-order wave equations discretized on standard staggered grids, using high-order derivative operators that are modified based on their relative position to the free surface. We extend the approach to VTI media to be able to model velocity anisotropy required in long-offset inversions. We then investigate the topography artefacts seen on real land full-waveform inversions in relatively simple synthetic experiments, allowing us to quantify the effect of elevation variation on the inversion accuracy. The experiments demonstrate that elevation variations in the order of 1/4 wavelength or somewhat smaller can already create artefacts in the inversion results if ignored.
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Global Visco-Acoustic Full Waveform Inversion
Authors N.V. da Silva, G. Yao, M. Warner, A. Umpleby and H. DebensSummaryFull Waveform Inversion aims to determine parameters of the subsurface by minimising the misfit between the simulated and recorded seismic data. The quality of such fit depends on many different aspects, as for example, the inversion algorithm and the accuracy of the constitutive laws. The latter is particularly important as if there are factors that are not taken into account in the seismic simulation then the inversion algorithm will compensate for their existence in the parameter(s) being estimated. One of such factors is attenuation. Here we introduce an approach that jointly estimates velocity and attenuation using a combination of Quantum Particle Swarm Optimisation with the conventional gradient descent method. This hybrid approach takes advantage of the fact that it is sufficient to estimate smooth models of Q and for this reason these can be represented with a sparse support, thus decreasing substantially the number of weights of the basis functions that have to be estimated and making the use of global algorithms practical. We demonstrate that the proposed method mitigates cross-talk between velocity and attenuation, while allowing the convergence towards accurate models of attenuation and velocity, thus being an effective method for velocity model building and consequently for seismic imaging.
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Addressing Viscous Effects in Acoustic Full-waveform Inversion
Authors O. Calderon Agudo, N. Vieira da Silva, M. Warner and J. MorganSummarySeismic waves are attenuated and dispersed as they travel through the subsurface given that part of the energy is lost into heat. These effects are visible on the recorded seismic data but are commonly ignored when performing acoustic full-waveform inversion (FWI). As a result, the recovered P-wave velocity models are not as well resolved and are quantitatively less accurate. Here we analyse the impact of viscous effects in acoustic FWI of visco-acoustic synthetic data and we propose and apply a method to mitigate attenuation effects while still performing acoustic FWI, which is based on matching filters. We show that only a smooth model of attenuation is required to successfully improve the recovered P-wave velocity model, even when applied to a noisy synthetic dataset.
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Mitigating Cycle Skipping in Full Waveform Inversion by Using a Scaled-Sobolev Objective Function
Authors M.A.H. Zuberi and R.G. PrattSummaryCycle skipping in the conventional full waveform inversion (FWI) objective function depends on the frequency content of the data, and on the error in the background velocity. The error in background velocity that can be tolerated without skipping cycles is determined by the half cycle criterion. However, the half cycle criterion is offset dependant so that far offsets in the data are more prone to cycle skipping than near offsets. This offset dependence of the half cycle criterion implies that the differentials of residuals with offset can be used as additional constraints in the objective function. In this study we introduce the scaled-Sobolev objective (SSO) that seeks to minimize a smooth version of the data residuals in addition to their derivatives in all data domain dimensions. The smoothing of the data is done using the scaled-Sobolev inner product (SSIP) in the data domain, resulting in an edge-preserving smoothing operator. In the absence of low frequencies, increasing the maximum order of derivatives in SSO is more important than the zeroth order scale factor. Initial results with synthetic data using the Marmousi model show that SSO can overcome a bulk shift in velocity of 30%, with a lowest frequency of 8 Hz.
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Sparse frequencies data inversion and the role of multi-scattered energy
More LessSummaryIn trying to extract a broad spectrum of model wavenumbers from the data, necessary to build a plausible model of the Earth, we are, in theory, bounded at the high end by the diffraction resolution limit, which is proportional to the highest usable frequency in the data. At the low end, and courtesy of our multi-dimensional acquisition, the principles behind diffraction tomography theoretically extend our range to zero-wavenumbers, mainly provided by transmissions like diving waves. Within certain regions of the subsurface (i.e. deep), we face the prospective of having a model wavenumber gap in representing the velocity. Here, I demonstrate that inverting for multi scattered energy, we can recover additional wavenumbers not provided by single scattering gradients, that may feed the high and low ends of the model wavenumber spectrum, as well as help us fill in the infamous intermediate wavenumber gap. Thus, I outline a scenario in which we acquire dedicated sparse frequency data, allowing for more time to inject more energy of those frequencies at a reduced cost. Such additional energy is necessary to the recording of more multi-scattered events. The objective of this new paradigm is a high resolution model of the Earth.
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Full Waveform Inversion for Elastic Waves: Macrovelocity Reconstruction with Realistic Frequency Bandwidth
Authors K. Gadylshin, G. Chavent and V. TcheverdaSummaryThe paper develops a reliable numerical method to solve inverse dynamic problem for elastic waves equation on the base of nonlinear least-squares formulation which is widely known as Full Waveform Inversion (FWI). The key issue on this way is correct reconstruction of macrovelocity component of the model with input seismic data without time frequencies less than 5–7Hz and reasonable source-recievers offsets. To provide correct macrovelocity reconstruction we introduce modified elastic FWI formulation which is sensitive to smooth space variations of both Vp- and Vs-velocity distributions
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Towards High Resolution Localised Elastic Full Waveform Inversion
Authors S. Yuan, N. Fuji, S. Singh and D. BorisovSummaryWe present a methodology to invert seismic data for a localised area by combining source-side wavefield injection and receiver-side extrapolation method. Despite the high resolving power of seismic full waveform inversion (FWI), the computational cost for practical scale elastic FWI remains a heavy burden. This can be much more severe for time-lapse surveys, which require real-time seismic imaging on a daily or weekly basis. Besides, structure changes during time-lapse surveys are likely to occur in a small area rather than the whole region, such as oil reservoir. We thus propose an approach that allows to image effectively the localised structure changes far deep from both source and receiver arrays. We perform both forward and back propagation only inside the target region. We present 2D elastic numerical examples of the proposed method and quantitatively evaluate the inversion errors, in comparison to those of conventional full-model inversions. The results show that the proposed localised waveform inversion is not only efficient and robust but also accurate even under the existence of errors in baseline models. Besides, the proposed strategy has the potentiality in determining highresolution imaging of reservoir by inverting higher frequencies (above 30 Hz) at relatively low computational cost.
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A Case Study of Monitoring Steam Flood Projects in Thin Vertically Stacked Reservoirs Using 3DVSP Technology
Authors A. Al-Mutairi, Z.B. Ren, J.R. Tinnin and S. RandazzoSummaryKuwait Oil Company (KOC) is undertaking an EOR project on a heavy oil field. This 3DVSP project was designed to monitor a 30-day steam injection into two reservoir sands which are separated by thin shale and top sealed by a thicker shale.
The goals of this project include creating a repeatable baseline survey for future 4DVSP purposes, acquiring high resolution data so individual thin reservoirs can be imaged, reservoir characterization analysis, and estimation of the steam chamber size after a 30-day CSS injection. Obtaining the highest possible frequencies was identified as a critical success factor for achieving these goals.
Extensive modelling and innovative customization of the acquisition design resulted in high resolution 3D seismic which provided surveillance and steam monitoring of thin vertically stacked reservoirs. The results demonstrated the steam flow direction was complex rather than a simple radial pattern. Reservoir characterization helped explain some of the complexity of the Cyclic Steam Stimulation program. Understanding the reservoirs, barriers, and effectiveness the steam floods will help determine where infill producer or injection wells need to be drilled to optimize production.
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Walkaway VIVSP - A Case Study Offshore UKCS for 2D Structural Omaging and Quantitative Interpretation
More LessSummaryThis paper is intended to demonstrate that a new approach to the acquisition of Vertical Incidence VSPs in deviated wells can provide significantly better results with little impact on acquisition times. We designed a fitfor-purpose 2D VSP walk above acquisition using the so called “walk-along vertical incidence VSP” (WAVI-VSP) technique to deliver the key borehole seismic objectives to reduce our current subsurface uncertainties:
- Seismic time-depth calibration
- A high resolution “vertical incidence” image below the wellbore
A deviated exploration well in the Central North Sea encountered hydrocarbons in a thin Palaeocene sandstone reservoir and was side tracked to find the OWC. The well was drilled based on seismic amplitude direct hydrocarbon indicator (DHI) and the reservoir is below the resolution of conventional seismic. A VSP is a direct approach to achieving the broadest seismic bandwidth and can guide the optimisation of the surface seismic to resolve the reservoir.
Key questions to address:
- Can the sand be resolved?
- How do we best image it to guide field development decisions?
- Is the DHI information consistent with the OWC in the well?
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Deep Structural Exploration in Zagros, SW Iran, Using Oriented 3-component VSP and Resistivity Borehole Wall Imager
Authors C. Naville, K. Kazemi and I. Abdollahie FardSummaryA deep exploration well was drilled down to 5300 m on the top of a surface fold in the mountainous Zagros in order to encounter a deep anticline at the top of Permian reservoir formation expected in the area. Due to poor surface seismic, geological and practical considerations were used for locating the well. The structural interpretation was refined during the drilling operation, using: well logs, borehole resistivity imaging, geological data, a 2D surface seismic and an intermediate VSP recorded using a three component (3C) sensor tool implemented with a Relative Bearing / Roll angle sensor.
The VSP data was processed before drilling the deep interval 5300m to 6130m Total Depth (TD), with the intention to predict any reflection below the intermediate 5300m drilled depth.
Next, the whole borehole data was further analyzed after reaching TD. The main focus was on independent extraction of dip/azimuth information from oriented 3C VSP data and from borehole wall resistivity measurements.
The highly folded structure encountered by the well and the absence of high energy seismic reflectors with substantial lateral extension detected by the VSP are coherent with the blurred results on the 2D surface seismic section in the well vicinity.
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Hard Rock VSP - The Case of the Missing P-wave
Authors M. Humphries and G. CampbellSummaryPrevious published examples have mentioned the lack of usable P-to-P-wave reflection image (PP-up) compared to the usable P-to-S-wave reflection image (PS-up) for hard rock platinum mining 3D Vertical Seismic Profiles (VSPs) in the South African Bushveld complex. We investigate the lack of PP-up amplitude in a rig source VSP acquired in an area of the Bushveld complex where the economic zone occurs with significant dip. The VSP clearly illustrates the problem of missing PP reflections in all types of VSP surveys and surface seismic far gathers in such hard rock areas. It is also a reminder that what might seem like a simple VSP still requires careful planning, processing and interpretation of all three components.
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Estimation of Intrinsic Q in Finely-Layered Media by Wavefield Inversion of VSP Data — Australian North West Shelf Case-Study
Authors A. Pirogova, B. Gurevich, R. Pevzner and S.M. GlubokovskikhSummarySeismic waves propagating through attenuative subsurface exhibit amplitude loss and distortion of frequency spectra. Proper description of attenuation process is required to compensate for these effects. Moreover, inelastic attenuation contains information on rock properties and could be utilized in attribute analysis for subsurface characterization. We propose to quantify inelastic (intrinsic) attenuation in horizontally-layered media by wavefield inversion of VSP data with respect to effective interval Q-factors. Impact of short-path multiples in finely-layered subsurface, i.e. scattering at stratigraphic boundaries, and other interference effects are taken into account by forward simulation over a high-resolution elastic model acquired from the well logs (resolution of 1.5m). We present a case study of approximate-zero-offset vertical seismic profile data from Wheatstone offshore site (Northern Shelf of Western Australia). First we describe the algorithm of 1D waveform Q-inversion. Then we validate it on the full-wave synthetics computed for the field survey geometry using a Global Matrix approach (OASES MIT code). Finally, we discuss the results of the Q-inversion application to the field ZVSP dataset versus Q-estimates by Centroid Frequency Shift method.
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Noise Sources in Fiber-Optic Distributed Acoustic Sensing VSP Data
Authors A. Ellmauthaler, M.E. Willis, X. Wu and M. LeBlancSummaryThis abstract details the three major noise sources affecting DAS VSP data and describes mitigation methods for each. The first noise source is fading, which occurs over spatiotemporally varying regions in the VSP records with extremely large amplitude values. It is caused by destructive interference of the backscattered light that changes with time. Acquiring repeated shot records and applying weighted stacking can mitigate this issue. Common-mode noise is the second noise source; it is caused by sound and vibration in the vicinity of the interrogator simultaneously imprinting on all data channels. This can be mitigated by extracting the signal that is common to all channels and subtracting it from each one. Temperature changes in the deployed fiber-optic cable or in the interrogator resulting in a low-frequency drift of the measured relative strain data is the third source of noise. While it is possible to low-pass filter the relative strain data, an easier approach is to convert the data to strain rate, which is less susceptible to temperature effects. This study shows that excellent quality DAS VSP data can be obtained by using an appropriate acquisition system, as well as by removing the effects of optical noise using simple processing algorithms.
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An Adaptive Filtering Approach to Noise Estimates for Use in Diversity Stacks for DAS Vsps
Authors M.J. Williams, J.H. Le Calvez, T. Cuny and A. HartogSummaryWe have investigated noise estimation in distributed acoustic sensing (DAS). We used an adaptive Wiener filtering method to construct noise maps. The resulting noise maps can be stored together with the images themselves and used in diversity stacks, which provide an uplift in time-lapse repeatability over linear stacking. We found that relatively large gains in VSP repeatability can be made from simple techniques.
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Borehole Seismic while Sampling Using FO Technology
Authors T. Kimura and K. GalybinSummaryThe combination of the hDVS/DAS technology and the high-strength hybrid heptacable technology is now enabling to record borehole seismic data while formation sampling operation called the “borehole seismic while sampling” method, which is the new way to minimize the rig time and the costs. This setup allows us to record borehole seismic data without adding dedicated operation time or rig time, which would be called “zero operation time borehole seismic acquisition”.
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Accuracy of Optimally Blended Methods for Wave Propagation
Authors V. Puzyrev and V. CaloSummaryWe investigate the optimal blending in the finite element method and isogeometric analysis for wave propagation problems. These techniques lead to more cost-effective schemes with much smaller phase errors and two additional orders of convergence. The proposed blending methods are equivalent to the use of nonstandard quadrature rules and hence they can be efficiently implemented by replacing the standard Gaussian quadrature by a nonstandard rule. Numerical examples demonstrate the superior accuracy of the optimally-blended schemes compared with the classical methods.
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Calibration of Frequency Decomposition Colour Blends Using Forward Modelling - Examples from the Scarborough Gas Field
Authors C. Han and P. SzafianSummaryThis study investigates using a combination of seismic forward modelling with frequency decomposition (FD) and colour blending analysis with the aim of better understanding what the major controlling factors on the frequency response are and how this impacts the spectral interference colour patterns observed in FD colour blends. Examples are provided using data from the Scarborough giant gas accumulation, offshore Northwest Australia. Forward modelling of reflectivity is common practice in the oil and gas industry, generally used to provide information on amplitude and phase changes which may occur in response to changes in a model. By incorporating frequency decomposition and red-green-blue (RGB) colour blending into the workflow there may be potential to detect subtle changes within the data, since the interplay between three band-restricted frequency volumes produces a colour blend which is extremely sensitive to frequency change and can often highlight features or trends not seen in full frequency or bandpass volumes. Increasing understanding of FD colour blends may aid in supporting or disproving interpretations made using other lines of evidence, as well as potentially allowing additional geological insights to be made, such as identification of facies, fluids, thicknesses and other changes in reservoir characteristics based on frequency response.
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Augmented Full Wavefield Modeling: An Iterative Directional Modeling Scheme for Inhomogeneous Media
Authors H.I. Hammad and D.J. VerschuurSummaryWe derive a representation theorem for modeling directional wavefields using reciprocity theorem of the convolution-type. A Neumann series expansion of the representation yields a series that is similar to that of Bremmer. A generalized Neumann series is also derived similar to that used for solving the non-directional Lippmann-Schwinger representation. An example shows how the series can model each scattering order separately for inhomogeneous media. This could potentially be useful in imaging and inverse problems.
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High-Order Leapfrog and Rapid Expansion Time Integrations On Staggered Finite Difference Wave Simulations
Authors O.J. Rojas, C. Spa and J. de la PuenteSummaryThis work is an exploratory study of coupling high-order time integrations to a finite-difference (FD) spatial discretization of the 1-D wave equation that combines eigth-order differencing at grid interior, with lateral formulas of order sixth and fourthat boundary neighborhood. This reduction of spatial accuracy at the grid vecinity of free surfaces is a known stability limitation of FD methods, when coupled to the two-step Leap-frog (LF) time stepping, which is widely used on seismic modeling. We first implement LF time integrations with an arbitrary accuracy order, as given from a standard Lax-Wendroff procedure, and compare results from the fourth-, sixth-, and twelfth order schemes, against the popular second-order LF. Our emphirical analyses establish the CFL stability constraints for propagation on an homogeneous medium, as first results, and then consider velocity heterogeneities when assessing dispersion and dissipation anomalies. Finally, we use a rapid expansion method (REM) to approximate the exponential of the semidiscrete FD discretization operator by a truncated Chebyshev matrix expansion. Althougth, REM has been previouslly applied to peudospectral (PS) wave simulations, this REM-FD scheme is the first reported in the technical literature according to our knowledge.
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Modelling of Time-varying Rough Sea Surface Ghosts and Source Deghosting by Integral Inversion
Authors E. Cecconello, E.G. Asgedom, O.C. Orji and W. SöllnerSummaryA major impediment to the full understanding of the data acquired in marine seismic is the restricting assumption of a flat and stationary sea surface used in certain pre-processing tools. A first step towards removing this assumption is to accurately account for the sea state (time varying free surface) in the deghosting process. On the receiver side, this is handled properly by using dual-sensor streamer. In this work, we present an integral approach to model the source side ghost effects from time-varying rough sea surfaces and show that the interaction with time-varying sea surfaces affect the subsurface reflections and may have a significant impact on seismic repeatability. We then continue with a theoretical derivation where we develop deghosting operator based on an integral inversion of the modeling operator. This formulation for source deghosting can account for the time-variation of rough sea surfaces.
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2D Wideline Feasibility Study — A Synthetic Example in Foothills
Authors J.M. Mougenot, A. Lafram, S. Tlalka, M. Appe and H. PuntousSummaryElastic feasibility study was performed on a foothills synthetic model. A special focus was put on signal to noise ratio of the modelled data to mimic real shots as much as possible. Blind processing sequence was performed leading to PSTM sections. True velocity model was used for PSDM imaging. Results show gain for wider and denser acquisition patterns. The replacement of dense crossline sampling by CRS seams questionable.
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Performance and Convergence of the Non-Periodic Homogenization for the 3D Elastic Wave Equation
Authors P. Cupillard and Y. CapdevilleSummarySeismic waves propagating in the Earth are affected by different sizes of heterogeneities. When modelling these waves using numerical methods, taking into account small heterogeneities is a challenge because it often requires important meshing efforts and leads to high, sometimes prohibitive, numerical costs. In the recent years, this problem has been overcome by applying the so-called homogenization technique to the elastic wave equation in non-periodic media. This technique allows to upscale the small heterogeneities and yields a smooth effective medium. In the present paper, we describe a 3D implementation of the method and we show that it can handle large and highly heterogeneous models with an acceptable speed and a good accuracy. This development opens the path to the correct account of the effect of small scale structures on the seismic wave propagation in complex 3D models of the subsurface.
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Directional Full-Wave Scatter Source Modelling and Dip-Sensitive Target-Oriented RTM
Authors M. Verschuren and M. Araya-PoloSummaryReverse Time Migration is now the dominant method to image complex geology. Nevertheless, illumination studies are still mostly done with ray-based methods, because wave-equation methods generally do not generate directional information, or only at considerable computational cost.
We introduce a simple way to numerically restrict the directional aperture of a full-wave source without distortion of the resulting wave front. At the location of the scatter source, a damping mask with chosen angular aperture, such as critical reflection angle, and direction, such as normal to structural dip, is applied in forward modelling time following a sine function that peaks at a small number of periods of the source wavelet.
The resulting scatter energy measured at the acquisition surface may be used in the same way as ray counts in myriad applications, such as in directional illumination or visibility analysis for survey design, and in target-oriented RTM shot selection. The main advantages of the proposed method are: implementation simplicity, computing efficiency, fidelity to the physics of wave propagation in complex geology, and stability across rugose velocity contrasts.
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Innovative and Interactive Methods Emphasizing Geological Events through Spectral Decomposition New Zealand Case Study
Authors B. Durot, M.M. Mangue, B.L. Luquet, J.P.A. Adam and N.D. DaynacSummaryThis paper presents how an interactive method in spectral decomposition can facilitate and improve processes in exploration. This study focuses on the Maui field, located offshore New Zealand, in the Taranaki basin. Its aim is to emphasize specific geological features by interactively performing spectral decomposition at different locations on surfaces generated from a Relative Geological Time (RGT) model. This model is obtained thanks to seismic interpretation based on horizon auto-tracking trough a grid (Pauget et al., 2009) and its refinement. It provides a new way to achieve a strata-slicing into the seismic data and allowing a quick and interactive navigation throughout the surfaces. By combining this workflow with the analysis of frequency variations along geological events, it is possible to get an enhanced spectral decomposition of geological features from their averaged spectral signature (low, medium and high frequencies). Each one of these key frequencies was mapped on surfaces and blended into a Red-Green-Blue (RGB) viewer. Such a technique allows the interpreter to better highlight turbidite channels which were then extracted as geobodies with a high rate of confidence.
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Seismic Spectral Decomposition for Reservoir Prediction In Glaciogenic Reservoirs
Authors F.J. Bataller Torre, A. Moscariello and N. McDougallSummaryThe present paper will focus on how to use Seismic Spectral Decomposition and RGB blending applied to a glaciogenic reservoir in Norht Africa aimed to obtain reservoir de-risking maps by calibrating and performing supervised classifications to Spectral Decomp outputs in order to be able to reduce uncertainties regarding the prediction of reservoir lithology, specifically in the case of non-reservoir, sub-seismic formations, which are not easy to predict.
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Interpretational Aspects of Multispectral Coherence
By K.J. MarfurtSummarySeismic coherence volumes are routinely used to delineate geologic features that might otherwise be overlooked on conventional amplitude volumes. In general, the quality of a coherence image is a direct function of the quality of the input seismic amplitude data. However, even after careful processing, certain spectral components will better illuminate a given feature than others. For this reason, one may wish to not only examine coherence computed from different filter banks, but somehow combine them into a single composite image. I do so by summing structure-oriented covariance matrices computed from spectral voices prior to computing coherence. I show that multispectral coherence images are superior to traditional broadband coherence images, even if the seismic amplitude data have been previously spectrally balanced. While much of this improvement can also be found in RGB blended volumes, multispectral coherence provides several advantages: (1) one can combine the information content of more than three coherence volumes, (2) there is only one rather than three volumes to be loaded into the workstation, and (3) the resulting grey-scale images can be co-rendered with other attributes of interest plotted against a polychromatic colour bar, such as P-impedance vs. Poisson’s ratio or SOM cluster results.
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