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79th EAGE Conference and Exhibition 2017
- Conference date: June 12-15, 2017
- Location: Paris, France
- Published: 12 June 2017
1 - 100 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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Using Wigner-Ville Distribution Properties for Thin Bed Identification
By C.J. StotterSummaryIn the search for ever more subtle reservoirs we often deal with hydrocarbon deposits, where the thickness of individual layers is below the seismic tuning thickness. Several methods were developed in the time and frequency domain to circumvent or go below this fundamental limitation of the seismic method. In this paper we investigate properties of the Wigner-Ville (WVD) time-frequency distribution, and especially of the cross-terms. We start with the mathematical definition of the WVD and investigate cross-term properties for two Gaussian time signals. We then examine the WVD of a wedge model and find that the cross-term shows variations even if the wedge thickness is below the tuning limit. We concentrate on the time location of the first-order minimum of the WVD cross-term which indicates the centre of the wedge even below the tuning thickness. Subsequently we apply this property for thin layer identification in a real seismic example. We conclude that tracking the location of the first-order minimum of the WVD cross-term can indicate the existence of layers below the tuning thickness in seismic data, and locate the mid-point between the top and base of the tuned layer.
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Multiscale Fusion for Improved Instantaneous Attribute Analysis
Authors M. Alfarraj, H. Di and G. AlRegibSummaryIn this abstract, we propose a multiscale approach for enhancing the resolution of instantaneous attributes, such as cosine of phase and phase dip, both of which tend to be highly sensitive to noise in seismic data. In particular, we use a multiscale representation, namely the Gaussian pyramid, to exploit seismic features at different resolutions followed by multiscale fusion to enhance both the quality and reduce noise sensitivity of these attributes. The value of the proposed technique is demonstrated through application on the Netherlands offshore F3 block, indicating its potential for improving more seismic attributes, such as coherence and curvature.
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Two Improved RGB Blend Methods Based on PCA and Brovey Transform
More LessSummaryWith the characteristics of effectively improving the limitations of single attribute analysis and making the results of reservoir description more reliable, seismic attribute fusion technology has been widely used in attribute analysis for years. RGB blend method fits well with the attribute interpretation and reservoir identification for combining various information of different frequency together. In this paper, we introduce two methods to improve the visual effect of the RGB attribute with the purpose of analyzing the attribute better and identifying the reservoir more easily. The two methods are both based on the RGB attribute, but better than it in effect, which is proved by the real data. The participation of full-frequency attribute and the intensity compensation in HSI colour space may be the main reasons.
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Generalized Spectral Decomposition and Its Use in Spectral Balancing
Authors W. Weinzierl, V. Aarre and S. CourtadeSummaryA new spectral balancing method based on a continuous wavelet transform is introduced. A hybrid spectral decomposition method, customizable to behave either as a short time Fourier or continuous wavelet transform, is used to decompose the input into its constituent frequencies. Anelastic attenuation processes are accounted for by construction of mother wavelets, being scaled and dilated. This new method is true-amplitude, lifting weaker amplitude frequencies to the same level as the amplitude of the strongest frequency band. The improvements within an interpretation context are evident when comparing the input and spectrally enhanced output. We test the new spectral balancing method on a 3D onshore survey acquired across the Teapot Dome structure, Wyoming. Previously unresolved features in the original amplitude are resolved on the spectrally balanced output. Spectral balancing provides additional information which often is obscured or masked by the limited bandwidth in conventional post-stack data.
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Continuous Coverage of Recent High Resolution Seismic and Magnetic Data gives New Insight into the Early Development of the Gulf of Mexico
Authors I. Deighton and F. WinterSummaryExtensive coverage of the entire Mexican Gulf of Mexico (MGoM) by long offset 2D marine seismic data, processed in time and depth, along with gravity and magnetic shipborne data were acquired on an evenly space survey grid during 2015–16 and enable a better understanding of the deep structure of the entire GoM. A correction of the GoM oceanic spreading transform fault locations, previously only diffusely identifiable on a Vertical Derivative version of the Sandwell Free Air Anomaly Map was carried out and a refinement of existing models of the extinct Jurassic-Early Cretaceous GoM spreading ridge locations was undertaken by coupling the above with gravity and magnetic grids and profile plots of seismic depth of top oceanic crust vs. distance. Due to thick sediment (up to 13 km) overlying the oceanic crust in the GoM, the magnetic anomaly signal and, therefore, the spreading anomaly pattern are more difficult to identify than those in younger and wider oceanic basins. Nonetheless, the location of the magnetic isochrons are readily identifiable by forward modelling of transform parallel transects within each spreading segment, and we are able to review existing models of oceanic opening time, rotation poles and spreading rates.
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Research of Seismoelectrical Effect
Authors S. Riabova and A.A. SpivakSummaryResearch of electric field variations in the propagation of seismic waves is of considerable interest for development of new techniques and methods to describe the structure of the crust and diagnosis of its geodynamic state. The intensity of the energy transformation of medium fluctuations in the electric field energy is largely determined by the properties of the environment and characteristics of its stress-strain state. It means that the response of environment on seismic influence as induced electrical signals contains information about the properties of the medium, stress operating in medium, and origin of its strains. We carried out a comparative analysis of amplitude variations in the field of seismic oscillations (waves of earthquakes, different types of local events, etc.) and synchronous with them variations in the electric field. The data analysis show the presence of seismoelectric effect in times of the seismic waves, which is well recorded in the absence of strong disturbances induced by other sources (the passage of atmospheric fronts, thunderstorms, strong winds, etc.). For the first time we obtained a quantitative relationship between the amplitude of the seismic and induced electric signal in certain conditions.
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Kinematics of a Silica Particle in the Deposition to Piping of Geothermal Power Plant
By M. IwataSummaryThe buildup of silica scale inside geothermal pipes and wells has serious impacts on the power generation efficiency in geothermal systems. There have been a large number of studies on controlling silica scale. However, silica deposition estimated by simple chemical kinetics cannot give a rational explanation of the complicated features empirically observed in laboratory and field experiments. The aim of this research is to investigate physical effects on silica particles and calculate scale precipitation rate quantitatively with a method of numerical simulation. We regarded silica scale as colloidal particles and analyzed the particle behavior by solving the motion equation of a particle. In this process, we computed the time required for the particle diffusion to the vicinity of wall surface by considering various physical reactions including hydrodynamic process, Brownian motion, particle-wall interaction, particle size, etc. In addition, we calculated the probability of particle re-entrainment from wall surface, which can be applied to CFD (Computational Fluid Dynamics). Our simulation results showed good agreement with an experimental data. Concerning the quantitative prediction of silica deposition, we emphasize the importance of physical effects on silica scaling.
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Appraising Structural Interpretations Using Seismic Data Misfit Functionals
Authors M. Irakarama, P. Cupillard, G. Caumon and P. SavaSummaryStructural interpretation can be challenging because of complex wave interactions and limited seismic bandwidth. A single seismic image can lead to multiple structural interpretations, reflecting structural interpretation uncertainties. Typically, this uncertainty is captured by generating several possible structural geometries. However, a quantitative assessment of the different possible structural interpretations is often difficult. In this paper we propose a methodology for assessing structural interpretations using seismic data misfit functions. We first develop a conceptual framework for solving such a problem before applying the method to a carefully designed synthetic study. Our results suggest that it is possible to appraise structural interpretation using seismic data if an appropriate misfit function is used.
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Estimating Detectability of Microseismicity with a Surface Monitoring Array Using Downhole Monitoring Array
Authors P. Wandycz, E. Święch, L. Eisner, D. Anikiev, A. Pasternacki and T. MaćkowskiSummaryWe analyze detectability of microseismic events by surface array using simultaneously deployed downhole array. We show that the detectability of the perforation shots on surface array can be assessed by the observations of the signals on the downhole array. Furthermore, we show that microseismic events weaker than the two detected perforation shots were not detected by the surface monitoring array and we show that later and stronger events would be potentially detectable if the surface array was not dismantled. This analysis allows us to determine the parameters of the surface array needed to carry out microseismic monitoring in this area of Poland.
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Non-double Couple Microseismic Events - Evidence from the Laboratory
Authors I.A. Vera Rodriguez and S. StanchitsSummarySource mechanism is an attribute of interest in acoustic emission (AE) analysis which has been used to determine the nature of failure during laboratory experiments. In this abstract, we present the results of the moment tensor inversion of AEs recorded during the hydraulic fracturing of a Colton sandstone block at triaxial stress conditions. The source geometries given by the biaxial decomposition of the moment tensor solutions contain a family of auxiliary planes lying parallel to the orientation of the main hydraulic fracture’s plane. During fracture propagation, most AEs were concentrated near the edge of the fracture, reflecting a tensile stress regime with opening angles mostly around 30 degrees. After breakdown, the pumps were reversed to withdraw fluid from the borehole. At this point, the stress field became compressive with AEs distributed across the complete face of the hydraulic fracture showing source mechanisms that reflected the closing of the fracture’s plane. Closing angles were in general lower in magnitude than opening angles.
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Evaluation of Nonlinear Approaches for Surface Microseismic Processing
Authors G.C. Michaud, C. Fliedner, A. Gendrin, T. Probert and A. OzbekSummaryIn the context of surface microseismic processing, a nonlinear stack method, the phase weighted nth root stack, was evaluated and benchmarked against linear stack. From a synthetic analysis, the parameter choice was evaluated to improve the detectability of small amplitude microseismic events. The choice and impact of small exponent values for the nonlinear stack method were confirmed on one stage of a multiwell, multistage hydraulic fracturing in the Marcellus shale formation. Compared to the linear stack, up to 30 % more events were detected and located for this data example.
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Reconstruction of the Near-Offset Gap in Marine Seismic Acquisition Using Radon-Domain Interferometric Interpolation
More LessSummaryWe demonstrate that interferometric interpolation implemented in the Radon domain can be used to fill the missing near-offset traces in marine data. We demonstrate the effectiveness of this method on synthetic data and a real towed marine dataset from the Baltic Sea. We compare the results obtained by Radon-domain interferometric interpolation with those from conventional interferometric interpolation. It is clear from this comparison that Radon-domain interferometric interpolation performs better than the conventional interferometric interpolation method when the acquisition geometry is irregular and the source-receiver aperture is limited.
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Resolving and Understanding Observed Azimuthal Anisotropy — A Case Study
Authors C.L. Smith, P. Reddy, A. Glushchenko, P. Vasilyev, P. Bilsby, A. Maycock, J.E. Vargas, Y.P. Utami and D. SturkoSummaryThis case study demonstrates that the regularization of single-sensor, single-source (S4) seismic data along discrete azimuth directions with regular source-detector distance intervals (radial domain gathers) can provide enhanced imaging through azimuthal velocity analysis, and deliver inversion-ready datasets with improved noise attenuation. A holistic workflow is presented that is tailored both to improve the final image quality, and to enable azimuthal amplitude variation with offset and azimuth (AVO/AVOAz) analyses, leading to the derivation of intrinsic rock property attributes leading to better reservoir management decisions & drilling plans. A prestack depth migration approach provides compensation for the overburden effect and improves resolution at the zone of interest by removing the effects of heterogeneities in the velocity field, which can be misinterpreted as azimuthal anisotropy.
The 2016 processing sequence of a dense, broadband 3D land seismic survey in Abu Dhabi supports the understanding that azimuth-rich S4 acquisition geometries can provide advantages over conventional techniques (such as the use of receiver arrays or narrow-azimuth surveys) for the imaging, fracture characterization, and reservoir management of very subtle low-relief structures, in particular shedding light on the complex geological environments of carbonate reservoirs in the Middle East.
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Frequency-dependent Azimuthal Effects on P-Wave Reflections from a Thin Layer
Authors Z. Jin, M. Chapman, X. Wu and G. PapageorgiouSummaryThis paper examines the impact of anisotropic dispersion on P-wave reflections. We show a modest effect on the amplitude and large effect on the phase, the latter of which could be mistaken for azimuthal velocity variations. We present a Bayesian inversion based on a forward modelling technique aimed at recovering layer thickness, fracture density, and fracture length in a thin-layer example. Our results show that the large-scale fractures can be clearly distinguished from microcracks despite the presence of interfering reflections, provided we have a sufficiently accurate background velocity model.
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A Study on the Regularization of OVG Data and the 3D Visualization Method
More LessSummaryOVG (Offset vector gathers) data is unable to be used for interpretation directly, although it is generated from wide-azimuth high-density acquisition through OVT (offset vector tile) migration and contains the anisotropic information. For getting visual 3D gather display and randomly extracting gather profiles and slices on the basis of OVT migration data, an offset-azimuth domain 5D interpolation method is proposed in this paper. By interpolating through rectangular rotation data regularization (RRDR) firstly instead of the conventional fan-shaped data regularization, it overcomes the shortage of the uneven folds between far and near offsets, improves the fidelity of data before and after the regularization, achieves the cylindrical display of OVG gather as well as the random extraction and display of the common offset gather, common azimuthal gather and time slices. It lays a good foundation for prestack anisotropy interpretation.
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Hysical Modeling Study of Seismic Responses of Fractured Zones With Varied Fracture Densities and Fracture Swarms
More LessSummaryThe seismic response characteristics caused by fracture parameters are the basis for fracture prediction and further analysis of tight fractured reservoir, and must be given great weigh and analyzed precisely. We mainly analyzes the seismic responses of fractures on post-stack sections in different azumuths, and the fractures include fracture swarms and fractures zones with varied fracture densities. The size of fractured zones and fracture swarms we simulate here is from dozens of meters to hundreds of meters which is unusual in physical modeling. The conclusions are as follows: The fractured zones with obvious boundaries have strong response of string of beads on the blank geological background of the thick bed. Fracture swarms piercing through multi-layers have characteristics of scrambled reflection, energy attenuation, wider events, the distortion and fault of events, most of these characteristics are weak reflection, these characteristics are azimuthal.
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MCMC Inversion of Offshore West Africa AVA Data
Authors G.M. Hoversten, A. Royle, J. Chen and D. MyerSummaryWe define the Bayesian posterior probability distribution in terms of the data likelihood, the prior distributions of unknown parameters, the prior distribution of lithology indexes and the prior distribution of data signal to noise. The prior distribution of lithology indexes is represented as a 3D Markov random field where the cell to cell coupling is parameterized using 3D Kriging parameters of angles and ranges. We show that the resulting PDFs of the geophysical parameters (Acoustic Impedance, Vp/Vs, and density) can be non-Gaussian (multi-modal).
We compare the MCMC inversion predictions of oil in place (OIP) and net-to-gross (NTG) to an industry standard work flow of simultaneous (SI) elastic joint inversion followed by Bayesian inference for porosity prediction. For the data set considered, which is representative of most West Africa data sets, the sampling based MCMC algorithm provides superior prediction of lithology and porosity, the two parameters that drive drilling decisions. Comparisons at two blind wells show that the MCMC NTG and OIP predictions are ∼ 5x better, in terms of % error, than the SI workflow. In this example an industry standard SI algorithm and workflow would significantly underestimate the OIP, which could have significant impact on a prospect’s viability.
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Application of a Markov Chain Monte Carlo-AVA Inversion Algorithm for Reservoir Characterization in Offshore Nile Delta
Authors M. Aleardi, F. Ciabarri and B. GarceaSummaryWe propose a formulation of Amplitude Versus Angle (AVA) inversion in terms of a Markov Chain Monte Carlo (MCMC) algorithm, and we show its application for reservoir characterization and litho-fluid facies prediction in a gas-saturated reservoir in offshore Nile Delta. A linear empirical rock physics model is used to link the petrophysical characteristics (porosity, water saturation and shaliness) to the elastic attributes (P-wave velocity, S-wave velocity and density), whereas the non-linear exact Zoeppritz equations are used to relate such elastic properties to the observed AVA responses. The exact Zoeppritz equations allow us to take advantage of the long offset seismic acquisition and thus to consider a wide range of incidence angles (between 0 and 60 degrees) in the inversion. The proposed algorithm, at the expense of a relatively high computational cost, reliably estimates the posterior probability distributions of the sought parameters, taking into consideration the uncertainties in the prior information, the uncertainties in the estimated rock-physics model and the errors affecting the observed AVA responses. The match between the predicted properties and the well log information demonstrates the applicability of the proposed method and the reliability of the results.
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Uncertainty Estimation of Inverted Elastic Parameters in Shale Reservoirs - A Case Study of Vaca Muerta Formation
Authors A.P. Kautyian Ziyisyian and F.G.E. SpäthSummaryIn shale formations, elastic characterization is key in deriving petrophysical and geomechanical properties, and the estimation of lateral variations in elastic parameters allow to identify good reservoir conditions for hydrocarbon production (sweet spots). To measure the lateral heterogeneity in the Vaca Muerta formation (VM), well logs were analyzed in the central part of the basin. This study shows that the lateral variation in Zp and Zs is about 28% and 24% respectevily, while the change observed in Vp/Vs and rho is less than 5%. The methodology to estimate the uncertainty in the inversion process involves synthetic seismic modeling and inversion for Zp, Vp/Vs and rho. Inverted parameters are compared to the model. To establish the dependandce of the inversion result with the quality of seismic data, different factors are tested: S/N, Angle Range and the number of partial stacks. Zp has the smallest relative error (less than 15%) and the highest correlation (above 0.9) for the entire Angle Range tested. The inversion of Vp/Vs has an acceptable relative error (less than 20%) when the angle range is above 40° and the S/N is higher than 9dB, for 3 stacks. For an angle range below 50° rho is not inverted.
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Well Tie Challenges in Southern Chad
Authors J. Wanstall and C. SandanayakeSummaryThis paper explores the impact of near surface noise on the ability to perform synthetic well ties to 3D land seismic data over a producing field.We conclude it is essential to understand the content of a seismic stack before embarking on well ties. Even more critical when poor quality data allows for a multitude of plausible tie solutions. If a single reflection boundary dominates ones well tie, one must be very sure its angle dependent characteristics are understood. Far from being an academic exercise, the product of this work included substantially altered time-depth functions utilised in time-depth conversion. It subtly changed the assignation of many critical surfaces in a field that consists of multiple stacked producing units. It altered our understanding of the phase of the seismic data. It also set hard limits on which reservoir properties could plausibly be derived from the seismic data in its current form whilst hinting that if the near surface induced noise could be effectively treated, lithological characterisation from seismic data is technically possible.
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Using AVO to Evaluate a Thin Pay - A Norwegian Case Study - An Update
Authors B. Paternoster, P.-O. Lys, V. Marlot and M. VedvikSummaryRecent progresses in seismic acquisition have paved the way for renewed prospect evaluations. In this paper, we present the example of a Palaeocene-aged prospect offshore Norway. It was identified several years ago but seen as non-economical.
A new broadband seismic dataset was used to re-interpret the prospect. AVO-based methods helped tackle the main difficulty associated to the poorly constrained geometry of this low relief prospect. Presumably, the seismic response of the prospective pay-interval results from the interference between a top hydrocarbon sand and an interpreted fluid contact within the massive sand body.
Nominally, this interval is thinner than seismic resolution. Taking advantage of the different AVA behaviors of these interfaces, top and base pay could be picked independently. Top reservoir was revisited shallower than previously and thickness estimated clear of tuning. Furthermore, the way amplitudes at a selected angle tune as a function of un-tuned thickness allowed de-risking the nature of the fluid fill in comparison with nearby oil and gas fields.
Finally, the well that was subsequently drilled proved the picking strategy right. The discovery confirmed the interpreted oil fill. This paper is an update of the original paper presented at the 76th Conference in Amsterdam.
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Avaz Analysis for Weak Azimuthal Anisotropy and Thin Layers: Case Study From the Lower Paleozoic Shale Play in Northern Poland
Authors M. Cyz and M. MalinowskiSummaryWe present application of Amplitude versus Azimuth analysis (AVAz) for weak anisotropy (1–2 %) and thin layers (up to 25 m) case for Lower Paleozoic shale play in Northern Poland. Feasibility study using synthetic AVAz response indicated that we could expect detectable azimuthal signature given the expected low crack density only in the wet case (fluid-filled fractures), but luckily liquid phase is observed is studied area. We applied AVAz analysis on large, wide-azimuth 3D seismic survey after full-azimuth (non-sectored) pre-stack depth migration. AVAz results were then compared with volumetric seismic attributes giving correlation in major fault zones. Furthermore results were corroborated by available well data: XRMI image logs giving confirmation of acquired AVAz azimuths and by cross-dipole sonic logs confirming anisotropy level.
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Stress Prediction Technology Based on AVAZ Inverison and its Application in Sichuan Basin of China
More LessSummaryIn this paper, we mainly talk about stress prediction technology, it has proven to be important and effective for shale gas evaluation and development. We use pre-stack AVAZ inversion to predict stress field, it is carried on pre-stack azimuthal gathers with constrained wells. A slight modification was made on the basis of Shaw’s (2004) equation in order to obtain elastic parameters such as P-wave impedance, S-wave impedance and fracture weakness from inversion. The stress indicator like DHSR (Differential Horizontal Stress Ratio) can be further estimated with P-wave impedance, S-wave impedance and fracture weakness. This work could help geophysicists and engineers better understand where engineer “sweet spot” is and guide well deployment. This method is applied in real data of Sichuan Basin, it shows that the result of stress prediction is effective and reasonable.
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A Robust FWI Method for Model Updating in High Contrast Bodies
Authors T. Martin, G. Pendred, J. Vermeulen, M. Bell and P. MellarSummaryWe present a robust method for Full Waveform Inversion (FWI), enabling the recovery of long-wavelength features of a velocity model. By using both transmitted and reflected waves the dynamically weighted FWI gradient enables high-resolution model building deeper than those achieved by diving waves alone. This reduces the dependency on long offset data acquisition.
The FWI approach uses a sophisticated regularization scheme to stabilize the inversion space. This methodology, which forms an extra constraint on the objective function, overcomes some of the limitations of the inversion in the presence of high contrast bodies. The implementation uses the split Bregman method, making it efficient and accurate.
We demonstrate the benefits of using the new gradient and regularization scheme by presenting the results on an intra-volcanic reservoir velocity model build from the Faroes-Shetland Basin.
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Application of Advanced Velocity Model Building and Migration Technology On Offshore North Africa Marine Dataset
Authors M. Pouget, C. Beigbeder, F. Gamar-Sadat, H. Prigent, M. Drubigny, L. Zerrouki and J.-M. MaillartSummaryIn recent years there has been tremendous progress made on the seismic migration and velocity model-updating technology to achieve better resolution and higher positioning accuracy, thus providing more valuable information to reduce exploration risk. In a dataset from offshore North Africa, the velocity model building is challenging due to a highly faulted geological setting and the presence of gas hydrates in the shallow overburden. Furthermore the image resolution beneath these diffracting and absorptive bodies is poor if we do not compensate for the resulting attenuation. This case study illustrates how a combination of sophisticated velocity update technologies, such as full waveform inversion and the latest tomography developments, together with Q-prestack depth migration, can achieve high quality seismic imaging.
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Risk Reduction On the Ivory Prospect Via Geologically Constrained Non-Parametric Inversion and Bayesian Uncertainty Estimation On a Fault-Bounded Reservoir
Authors J. Raffle, T. Earnshaw, J. Fruehn, S. Greenwood, J. Singh, C. Hagen, R. Felicio, D. Sassen, Z. Luo, S.I. Forsund, M. Ackers, L. Aamodt and I.F. JonesSummaryThe Ivory discovery lies within the Nyk High, located in the north-eastern part of the Vøring Basin, which has been tectonically active in several phases. The main challenge in mapping the extent of the Ivory discovery has been seismic imaging at the crest of structures bound by major faults (e.g. fault shadow effects), together with depth conversion uncertainty and a poor well to seismic tie. To address the uncertainties associated with these issues, a new Pre-Stack Depth Migration was run using a dataset re-processed with the latest demultiple and deghosting technology. From this final migrated volume, structural uncertainty was then estimated using a Bayesian statistical analysis of the tomographic resolution matrices in conjunction with prior uncertainty estimates.
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Multiphysics Earth Model Building Via Simultaneous Joint Inversion of Seismic and Gravity Data for Faulted Thrust-Belt Imaging Challenges
Authors M. Speziali, A. Pawson, M. Mantovani and L. MasnaghettiSummaryThe integration of independent geophysical data sets allows reducing the risk and increasing the confidence when exploring complex geological settings, therefore maximizing the return on acquisition investment. In this context, gravity data are a successful candidate for the integration with seismic data, because of the limited acquisition cost and the excellent petrophysical similarity observed between velocity and density.
The maximization of the benefits attainable from combining multiple geophysical data sets is achieved when a quantitative approach, such as the simultaneous joint inversion (SJI), is implemented. Moreover, the integrated approach should be consistently applied throughout the whole geophysical processing and imaging sequence, encompassing time processing, near surface characterization and depth imaging.
The fulfillment of both the aforementioned conditions is desirable for solving complex geophysical challenges, such as faulted thrust-belt imaging, as discussed based on a case study from southeast Asia.
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Reconstruction Chronostratigraphy in Carbonate Reservoirs Surrounding Wrench Fault Zone of RMKS, Sakala Subbasin, East Java Basin, Indonesia
Authors M.S. Indah, M. Natsir, D. Kadar and J. SetyowiyotoSummary- Complex carbonat and Kujung contain oil and gas for exploration show at exploration well
- Complex Kujung reservoir domain for reservoir characterisation based on fossil absolute, vuggy & fracturing, and sedimen structure data core
- oil and gas prospective resources finding for 1 TCF and 1,68 BBOE
- System Track including for TST 1, HST 1, TST 2, HST 2, TST 3, HST 3
- Marker chronostratigraphy inclusing SB 0/34 MA, MFS 0/33 MA, SB 1/32 MA, MFS 1/30,5 MA, SB 2/28 MA, MFS 2/26 MA, SB 3/23 MA, MFS 3/ 22.3, SB 4 /21,5 MA
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Sequence Stratigraphy, Depositional Environment and Numerical Stratigraphic Modelling of the Orphan Basin (NL, Canada)
Authors P. Jermannaud, E. Le Guerroué, J. Pitz, T. Pichot, D. McCallum, I. Atkinson, V. Mitchell and R. WrightSummaryA sequence stratigraphic analysis coupled with a 3D forward stratigraphic model was performed in the Orphan Basin (NL, Canada). It aimed at understanding the sedimentary and stratigraphic infill of the basin and to define potential plays.
The basin sequence stratigraphic architecture was initially defined using two composite 2D seismic sections. This stratigraphic framework was then applied in 3D space using the complete seismic and well dataset to create eight (8) conceptual Gross Depositional Environment (GDE) maps.
The conceptual GDE were then numerically tested using the 4D forward stratigraphic modelling tool DionisosFlow™. The model allowed the paleoenvironment interpretation to be greatly refined, and the lateral and vertical extension of potential reservoirs on the shelf margin and within large turbiditic complexes to be identified. Transgressive intervals were highlighted to be favorable to the deposition and preservation of organic-rich sediments.
The 3D stratigraphic grid results were used to assess the exploration geological risk, considering reservoir/seal presence and effectiveness. Sand and shale distribution in the 3D stratigraphic model is available laterally and vertically in terms of Net sand, Net to Gross and as a minimum continuous thickness. Reservoir / seal couplets, defining plays, were risked (Common Risk Segment mapping) with accurate spatial definition.
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Albian Clastic Prograding System in the Dunga Field (Western Kazakhstan) From Regional Understanding to Prospectivity
Authors M. Dujoncquoy, A. Arvidsen and P. HillockSummaryThe Lower Cretaceous series of the Mangyshlak Basin in Western Kazakhstan mainly consists of clastic sediments characterizing continental to marine depositional environments. The overall basin records at that time a large wavelength subsidence without major faulting, involving eustasy as the main controlling factor on sedimentation. The lower to middle Albian interval in the Dunga license is characterized in seismic by a set of well-imaged clinoform geometries prograding from East to West at the base, passing upwards to more sub-parallel and horizontal reflections. The clinoform sequence in the lower section is interpreted to represent a shoreface/delta environment. The upper interval is interpreted as an extensive aggrading offshore to shoreface environment. The complex stratigraphic architecture of this clinoform system creates lateral and horizontal facies changes, increasing the chance of stratigraphic traps with internal reservoir-seal pairs. The Albian play has initially been proved by Maersk Oil in 2012, and further prospectivity is supported by the indications of hydrocarbons identified on wireline logs and mudlog data. A geological model has been constructed based on seismic interpretation of geometries, facies analysis from multiple wells and core data in order to better understand the remaining prospectivity within this sedimentary system.
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High-Resolution Reservoir Architecture Modelling of Thin-Bedded Fluvial Terminal-Splay Sandstone in the Rotliegend Feather-Edge Area
SummaryRotliegend aeolian and fluvial sandstones are prolific gas reservoirs throughout the Southern Permian Basin (SPB). Exploration and research efforts concentrated on the sand-dominated southern flank of the SPB, where the major gas fields are located. The reservoir potential of the Rotliegend feather edge in the central part of the SPB, i.e. the area where the south-derived sands pinch out towards the Silver Pit salt lake, has long been underestimated. The sand-starved, claystone-dominated and evaporite-bearing lithology in the central part of the basin hampered the detectability of thin-bedded, potential reservoir sandstones with conventional well logs. The present study uses high-resolution well correlations in a sequence-stratigraphic framework. The employed methodology is a combination of pattern analysis (trends and trend changes) in gamma-ray (GR) logs, and maximum entropy-based (MEM-based) spectral trend curves of GR to graphically evaluate the validity of the pattern analysis. This allowed for the correlation of at least twelve individual thin-bedded sheets (1–2m thick) a 20–25m thick reservoir interval over distances larger than 20km. Core analysis has identified the sheets as unconfined fluvial terminal-splay sandstone. The facies characteristics and sedimentary architecture were corroborated in an outcrop analogue study of a present-day river system in the Altiplano Basin (Bolivia).
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Multidimensional Gravity Gradient Modeling for 3D Salt Delineation in the Nordkapp Basin
Authors S. Panepinto, I. Guerra, M. Mantovani and L. MasnaghettiSummaryWe present an alternative and cost-effective approach for 3D salt delineation in frontier exploration areas. Our integrated multi-physics workflow combines the vertical tensor components of FTG data, anomaly enhancement techniques, interactive interpretive 2D modeling and 3D forward modeling for salt mapping. The benefit of the proposed approach is the ability to build a first-order 3D salt distribution over a wide area to assess salt volumes. The method was applied to a large FTG survey acquired in the Nordkapp Basin, Norway. Finally, the integrated multi-physics solution can be exploited for 1) Defining the sediment vs. salt ratio in salt basins, 2) Delineating areas of particular interest in terms of exploration prospectivity, 3) Identifying areas of broad salt overhangs, and 4) Ranking salt volumes for more refined 3D seismic acquisitions.
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Gravity Inversion By The MHODE Method: Application To A Salt Dome Case
Authors M.S. Chauhan, M. Fedi and M.K. SenSummaryWe present a new method involving the inversion of the scaling function, a quantity that is calculated along the ridges in 3D space. The inversion is based on the Multi-HOmogeneity Depth Estimation (MHODE, Fedi et al., 2015 ) and enjoys the important feature of not being dependant on density, but only on the source geometry. In order to perform the inversion, it is necessary first to compute the scaling function directly from the data in 3D space along the ridges ( Fedi et al., 2009 ; Florio and Fedi, 2014 ) and this step can be done by computing the field at different levels. We used 2D Talwani’s formula as forward problem ( Talwani et al., 1959 ). A set of non-linear equations is then formed, where the unknown quantities are the source coordinates. We used the Very Fast Simulated Annealing (VFSA) algorithm ( Ingber, 1989 ; Sen and Stoffa, 2013 ) to solve such a system. We will show the application of our approach to the synthetic example of a salt dome like structure having an inhomogeneous density contrast and a real case of the Mors salt dome (Denmark).
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Estimating the Curie Point Depth Using Magnetic Field Data to Assess the Geothermal Potential
Authors J. Drolet, B. Giroux and C. BouligandSummaryNew technologies that allow geothermal energy production in colder conditions result in interest for geothermal exploration in low heat flux regions. The Province of Québec, eastern Canada, is such a case. Mapping the Curie point depth (CPD) is appealing as an exploration tool due to the scarcity of the direct data. We have revisited a methodology to estimate the CPD using a fractal source distribution model and aeromagnetic data. Our methodology relies on a statistical model of crustal magnetization having a constant magnetization direction and random magnetization amplitude. The shape of the radial average of the logarithm of the power spectrum of magnetic anomalies is predicted using this model. The model parameters (thickness and depth to the top of the magnetic layer, the fractal exponent β and the constant C’) are obtained by calculating the best fit between the theoretical and observed radial power spectra using a non-linear least-square algorithm. Rather than using a constant value for the fractal exponent β, we propose a new calibration workflow based on heat flux measurements and lithology. This workflow includes the use of normal kriging of heat flux data. Mapping the CPD will help identifying potential areas for further detailed exploration programs.
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3D Potential Field Data Using L0 Norm Constraint Via Compressive Sensing
More LessSummaryI introduce sparse constraints into potential field data inversion to obtain the sparse inversion results. The sparse constraints have now been used in many types of geophysical domains, such as geophysical data processes. The new stabilized is a common practice, which should be minimized in the inversion method. This new inversion method mainly obtains the sub-surface nonzero density contrast, and the gravity data produced by the nonzero density contrast must fit the observed residual gravity data. Emphasizing L0 norm sparse constraints ensures that the inverse results are simple, and no unnecessary structures are expected as required by the potential field data. Minimizing the quasi-norm tends to penalize smooth variations, and it promotes a more blocky character in the solution. It is well known that the minimization of the L0 norm is an NP-complex problem in combinatorial optimization, which indicates that optimization algorithms solving the problem cannot be completed in polynomial terms. There are several methods to solve this NP-complex problem. In this paper, this sparse-constraints norm has been imposed on the gravity data inverse problems to obtain the density contrast distribution.
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SOM Clustering Analysis in the Discrete Wavelet Transform Domain for Filtering Noisy Magnetotelluric Data
Authors R. Carbonari, L. D’Auria, R. Di Maio and Z. PetrilloSummaryDespite the magnetotelluric method (MT) is one of the most prominent geophysical technique for deep subsoil exploration, it is not yet completely reliable when applied in urban or industrialized areas due to the presence of anthropic electromagnetic noise. The latter, indeed, may severely affect the MT recordings and, as a consequence, the impedance tensor estimates, which allow to retrieve the apparent resistivity values describing the underground electrical behaviour. In this work, a new filtering approach for MT data denoising is proposed. The procedure is based on the clustering of the impedance tensor estimates by using the Self-Organizing Map (SOM) neural network model. The clustering is performed in the time-frequency domain by a discrete wavelet transformation of the MT signals. In addition, a criterion for selecting, in each wavelet scale, the clusters that lead to the most reliable apparent resistivity estimates has been suggested. The application of the proposed filtering approach to synthetic MT signals has shown that the SOM clustering is very sensitive to the presence of noise and that it is possible to get consistent apparent resistivity curves.
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Controlled Source Boat-Towed Radio-Magnetotellurics for Site Investigation At Äspö Hard Rock Laboratory, Southeastern Sweden
Authors S. Wang, M. Bastani, T. Kalscheuer, A. Malehmir and L. DynesiusSummaryThe radio-magnetotelluric (RMT) method has traditionally been used for land investigations. However, with the development of the boat-towed RMT system, this method is used on shallow water. The lowest frequency of the RMT method is about 14 kHz and in addition water resistivity is quite low in some cases, therefore controlled source measurements is naturally considered for data acquisition. In order to resolve a fracture zone under a brackish water body, the controlled source boat-towed RMT (CSRMT) approach was tested. CSRMT and RMT one-dimensional inversions were carried out separately to analyze galvanic distortions and source effects in our dataset. Serious distortions observed in both inversions as well as the two-dimensional (2D) structure observed in our previous study made us consider 2D inversion for modeling the data. Due to the sufficiently large distance between transmitter and receivers, the CSRMT data were inverted using a 2D inversion code originally designed for plane-wave RMT data. Occam and damped Occam schemes were used in our 2D inversions for CSRMT and RMT data. The results show that CSRMT can better resolve the fracture zone than RMT. This study further illustrates the use of the boat-towed RMT system and particularly when combined with controlled source.
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First CSEM Surveys with a Newly Designed Receiver
Authors S.L. Helwig, W. Wood and Ø. FrafjordSummaryA new receiver design for marine CSEM, mainly intended to be used in vertical-vertical CSEM, where both the transmitter and the main receiver component are oriented vertically, was operated in two field surveys for the first time. The design differs strongly from other CSEM receivers and is based on a central vertical pole hinged in a tripod frame. It overcomes previous restrictions in receiver count and operational efficiency in vertical-vertical CSEM.
In combination with a vertical 5000A source dipole, 3D data acquisition with 72 receiver positions and 77 pulse positions was performed.
Noise levels from acquisition in the Barents Sea and in the Norwegian Sea were close to each other with a slight advantage in the Norwegian Sea. Data from the Barents Sea shows a stronger 12h noise period in the frequency range from 3 to 4Hz. This is in agreement with stronger tidal motions in the Barents Sea.
As more receivers are used at the same time the new data sets benefit from additional longer offset data not available in previous data sets. It allows for new ways of processing. Influences from induced polarization for example are offset dependent and can be analyzed in more detail.
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The Next Generation Electromagnetic Acquisition System
Authors A.K. Nguyen, P. Hanssen, R. Mittet, H.R. Jensen, L.T.T. Fogelin, M. Skarø, M. Rosenquist and P. van der SmanSummaryWe have compared field test data from a next generation node based CSEM acquisition system with data from a reference conventional system in a shallow water environment. The next generation system with much higher transmitter dipole moment and more sensitive receivers provides a step change improvement in the data quality, with clean data for all source frequencies out to 20 km offset compared to around 10 km offset for the reference system. The high data quality also provides clear improvements in the inversion results. This was demonstrated by improved imaging of a hydrocarbon accumulation under challenging conditions. We expect a maximal imaging depth, relative to the seabed, of up to 4500 m in future surveys with a commercial version of the next generation acquisition system.
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Why You Should Take Caution in Using Rock Physics Model Approximations for Time-lapse Analysis
More LessSummaryRock physics models are used as a method of modelling the influence of production-related stress change on seismic velocities. Many different models exist, however, almost all require either stress-velocity core data or complex laboratory techniques (e.g. X-ray diffraction) to calibrate. This becomes an issue when core data is not available, which is often the case for non-reservoir rocks. In these circumstances, approximate rock physics models may be applied, which use simplified formulae derived from best-fit parameters to constrained core datasets. However, in this study we show why you should take caution in using such relationships. Although they may provide good approximations of the absolute magnitude of the rock velocity, they are limited in predicting time-lapse changes in seismic velocity due to stress. This is because of the difficulty in relating parameters that govern the shape/curvature of the nonlinear relationship to best-fit constants or abundant rock properties. Although we use only simple isotropic relationships in this study, the conclusions remain applicable to all models, including anisotropic ones. This study also demonstrates the important of an accurate rock physics model in time-lapse monitoring scenarios. We show that just small discrepancies in model parameters can lead to large differences in predicted time-lapse velocities.
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Pressure Effects on the Joint Elastic-electrical Properties of Shaly Sandstones Based on Clay Distribution
Authors N. Aladwani, L.J. North and A.I. BestSummaryThe effect of pressure was tested on to a joint ultrasonic and resistivity datasets for 67 shaly reservoir sandstones classified into four groups according to clay distribution. We investigated the role of pore-filling and load-bearing clay on the pressure-sensitivity of the relationships between resistivity and velocity (G1), resistivity and attenuation (G2), and velocity and attenuation (G3).The results give useful information for joint property model development for improved hydrocarbon reservoir characterization.
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Dispersions and Attenuations Phenomena on Sandstones Poisson’s Ratio
Authors L. Pimienta, J. Fortin and Y. GuéguenSummaryWhen acquiring and interpreting seismic data at the field scale, one aims to gain insights on the rocks travelled through as well as the saturating fluid. One interesting property for such studies is the Vp/Vs ratio that allows insights independently of the density effects. Assuming the media to be isotropic, this ratio directly relates to Poisson’s ratio, an intrinsic property of the rock. Over the last decades, dispersion and attenuation effects were shown to occur on Vp and Vs, but Poisson’s ratio is often assumed to be independent of the measuring frequency.
In this study, provided that dissipation phenomena are observed on the elastic constants, it is shown theoretically that the same is expected for Poisson’s ratio. Moreover, measurements on a viscoelastic material and a poroelastic rock confirm this observation. For the rock sample, the measured dispersion/attenuation phenomena are large when fluid pressure is high or confining pressure is low. At the field scale, Vp/Vs ratio would indeed be a clear proxy of a high fluid pressure, and the ratio in attenuations could be a very interesting asset.
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Effect of Incident Angle on Wave Scattering in Fractured Media - A Numerical Experiment Using an Integral-based Approach
Authors H. Liu, M.K.S. Sen and K.T.S. SpikesSummaryIn this work, we numerically simulate seismic wave propagation in realistic fractured media to investigate characteristic scattering patterns. The linear slip model is used to describe the displacement discontinuity across the fracture. An integral approach, based on an element-level of discretization, is implemented to simulate elastic wave propagation. We used two typical incident angles, 0 and 90 degrees, to investigate their effects on scattering patterns, quantified by their scattering indices. The results show significant variations in wave scattering with different incident angles. More specifically, scattering indices are symmetric for both incident angles. However, the scattering index for the 90-degree incident angle displays a much more spatially distributed pattern than does the index for 0 degrees.
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Experimental Investigation of Clay Content on Brittleness of Synthetic Shale
More LessSummaryIt is important to understand that the brittleness of shale is a combined response of minerals composition, pores, fluids in pores, and micro-structure of rock at certain temperature and pressure. However, clay content as a key parameter that affect the brittleness of shale, has not yet been well studied and understood. In this paper, we focus on impact of clay content on the brittleness of synthetic shale with different clay content. To reduce the number of unknown factors caused by multiple minerals, we made 8 samples each with a different weight percent of mineral: 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, instead of natural shale. The results indicate that with the higher clay content, samples show higher Young’s modulus, higher brittleness and lower Poisson’s ratio, which may be attributed to the increase of amount soft component (clay mineral). Besides, bedding plane has a significant impact on mechanical properties, E11 is always larger than E33 and B11 is always larger than B33. For the anisotropy of mechanical properties, ΔE and ΔB increase with the increase of clay content, contrarily, Δv decrease with the increase of clay content.
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Optimization of Brittleness Estimation Using Rock Physics Templates
More LessSummaryThe absence of a universally accepted definition and measurement of brittleness in shale gas plays has led to various methods or models for its quantification. To enhance the reliability of brittleness for evaluating reservoir quality, the paper proposes to optimize the brittleness estimation using rock physics templates. It begins with constructing a rock physics workflow to link the elastic properties of shales to complex constituents and specific microstructure attributes, followed by calibration with well log data, the constructed rock physics template could be used for geophysical prediction of porosity and lithology. Last, the brittleness index defined in terms of mineralogy and different geomechanical parameters based on the template is investigated. Consistent with the well-derived brittleness analysis, the constructed templates show great potential for deciding a better brittleness indicator in practice and enhancing the applicability of well log and seismic data for the estimation of brittleness.
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Estimating Anisotropic Brittleness of Shale Based On a New Rock Physics Model
More LessSummaryIt is widely known that shale often shows high anisotropic property. Ignoring shale anisotropy can induce errors in brittleness estimation. However, in oil industry, the common way to evaluate the brittleness of shale is based on using isotropic parameter (i.e. Young’s moduli and Poisson’s ratios), since it can be easily calculated based on measured elastic wave velocity from geophysical data. Anisotropic shale rock physics modeling offer us a new way to estimate the brittleness of shale from anisotropic aspect. Our studies firstly introduce a new rock physic model for shale. Based on our anisotropic shale model. The relationship between physical properties (like pore geometry, TOC, shale lamination and dip angle of shale formation) and elastic parameters (like anisotropic YM and PR) are established. Our modeling results coincide with the real data points of shale. The prediction shows the vertical/horizontal YM always below 1 while the vertical/horizontal PR can be either over or below 1. We find different extent of shale lamination may be the reason to explain the random distribution of Vani. And the brittleness of shale can vary significantly while drilling due to the strong anisotropy of shale formation.
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Random Noise Attenuation by Planar Mathematical Morphological Filtering
More LessSummaryImprovement of the signal-to-noise ratio (S/N) of seismic data is necessary in many seismic exploration areas. The attenuation of random noise is an important subject in improving the S/N. Geophysicists usually utilize the difference between signal and random noise in certain attributes, such as frequency, wave number, or correlation. In this paper, we have proposed a novel method utilizing the planar morphological attribute of seismic data to separate signal and random noise. The extraction of the morphological attribute is implemented by the planar morphological operations. The attenuation of random noise is achieved by removing the energy in the smaller morphological scales. We have named our proposed method planar mathematical morphological filtering (PMMF). Application of PMMF on synthetic and field seismic data demonstrates superior performance compared with the 2D median filtering and the singular spectrum analysis (SSA) method.
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Adaptive Seismic Random Noise Attenuation Using Curvelet Transform
More LessSummaryThe sparse inversion based random noise elimination methods utilize the soft threshold operation to realize denoising on the basis that seismic signals have sparsity expression in a transformed domain. The threshold values are very crucial for the final inversion results, they should match the energy of noise. However, the energy of noise is hard to achieve, the popular method to get proper threshold values is try many times manually which will cost much computation resource and labor. This paper proposed an adaptive random noise elimination method without any a priori information using the curvelet transform as the sparse transform, the inner relation between the sparsity of solution and residual with the iteration can be used to decide a proper threshold value, thus suitable denoising results can be provide based on this idea. Numerical experiment demonstrate that the proposed method can protect valid signal, eliminate random noise, render the events clear and improve signal-noise-ratio and resolution of seismic data.
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Curvelet-transform-based Random Noise Attenuation Using Energy Mean Scanning in f-k Domain
More LessSummaryThe curvelet denoising method has been successfully applied to seismic random noise attenuation. However, The conventional curvelet denoising method based on thresholding algorithm fails to preserve weak reflected signals in seismic events which have complex geometric structure. In this paper,we propose a novel curvelet denosing algorithm that applies the curvelet transform to 2D Fourier-transformed data in the fk domain instead of original data in the tx domain. In f-k domain in which the energy of the events with similar moveouts and diverse amplitude is located closely. Thus, we can take advantage of the energetic aggregation to preserve the weak reflected signals. Furthermore, an energy mean scanning algorithm based on the energetic statistical difference between effective signal and noise is proposed to perserve effective signal. The application on synthetic shot record and real imagration data demonstrates the feasibility and effectiveness of our proposed method.
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Adaptive Empirical Wavelet Transform for Seismic Noise Reduction
More LessSummaryDenoising is of great importance in seismic data processing. A variety of denoising methods have been proposed in the past several decades. However, it remains a longstanding problem to effectively separate noise and useful signal in the 2D/3D data set. In addition, seismic denoising is often performed trace by trace and the lateral continuity is usually not taken into consideration. To solve these two problems, we propose a novel method named adaptive empirical wavelet transform (AEWT) for seismic random noise reduction. In the AEWT, we take advantage of the outstanding denoising performance of EWT and the lateral continuity of multidimensional seismic data. When dealing with 2D data sets, the AEWT considers the spatial lateral continuity between the traces using the dominant frequency criterion (DFC) method, which selects the intrinsic mode functions by adaptively judging the dominant frequency of each trace. Both 2D synthetic and field data examples show successful performance of the proposed AEWT.
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