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**File Type**

3D general surface multiple prediction (GSMP) is an accurate and flexible implementation of 3D surface-related multiple elimination (SRME). We use a case history from the Northwest Shelf to demonstrate the effectiveness of the algorithm. A feasibility study explores the utility of reprocessing the existing data with 3D SRME, and improvement in velocity model delineation is predicted. Assuming that all traces have source-to-detector azimuths aligned with the nominal grid is an approximation exploitable when designing 3D SRME algorithms in order to simplify implementation and reduce cost. One of the major advantages of 3D GSMP over such methods is its ability to predict multiples corresponding to the true acquisition geometry. A comparison of results corresponding to multiples predicted with nominal- and true-azimuth geometries clearly shows the improvement in demultiple performance for the latter case. Compute cost is a concern for all 3D SRME algorithms, and is related to the sampling and aperture used for the multiple contribution gathers. We show how these parameters may be optimized to control the compute cost without degrading results. A substantial improvement in image quality is obtained following reprocessing with 3D GSMP, even where the multiples are not strong compared to the signal.

SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)

Sourbier, Florent (Géosciences Azur CNRS) | Operto, Stéphane (Géosciences Azur CNRS) | Haidar, Azzam (CERFACS) | Giraud, Luc (ENSEEIHT-IRIT) | Virieux, Jean (University Joseph Fourier of Grenoble)

We present a parallel domain decomposition method for frequency-domain modeling of wave propagation. The domain decomposition method, based on the Schur complement method, uses an hybrid direct-iterative solver. The main interest of mixing solvers is to overcome the huge memory complexity of direct solvers while partially preserving the efficiency of multi-RHS simulations and mitigate the iteration count in iterative solvers. To improve the convergence rate of the iterative solver, a preconditioning provided by the local assembled Schur complement is used. Discretization of the time-harmonic wave equation (Helmholtz equation) is based on a parsimonious staggered finite-difference grid method but the domain decomposition method could apply to any numerical scheme such as finite-element or finite-volume methods. We developed this method as a tool for frequency-domain fullwaveform inversion.

Frequency-domain full-waveform inversion (FWI) has been extensively developed during last decade to build high-resolution velocity models (Pratt, 2004). One advantage of the frequency domain is that inversion of a few frequencies are enough to build velocity models from wide-aperture acquisitions. Multisource frequency-domain wave modeling requires resolution of a large sparse system of linear equations with multiple righthand side (RHS). In 2D, the method of choice for solving these systems relies on direct solver because multi-RHS solutions can be efficiently computed once the LU factorization of the matrix was computed. In 3D or for very large 2D problems, the memory requirements of direct solvers precludes applications involving hundred millions of unknowns. To overcome this limitation, we investigate a domain decomposition method based on the Schur complement approach for 2D/3D frequency-domain acoustic wave modeling. The method relies on a hybrid direct-iterative solver. Direct solver is applied to sparse impedance matrices assembled on each sub-domain, hence, reducing the memory requirement of the overall simulation. Iterative solver based on a preconditioned Krylov method is used to solve the interface nodes between adjacent domains. A possible drawback of the hybrid approach is that the time complexity of the iterative part linearly increases with the number of RHS, if single-RHS Krylov subspace method is sequentially applied to each RHS.We mention that block-Krylov techniques or deflation techniques can be used in that case to partially overcome this effect. In the following, we introduce the domain decomposition method before illustrating its features with 2D and 3D simulations.

The domain decomposition consists of splitting the computational domain into sub-domains without overlap. Each subdomain shares interface nodes with its adjacent sub-domains. Such decomposition is referred as sub-structuring schemes (Saad, 2003; Smith et al., 1996).

We applied both the direct and the hybrid approaches to the 2D Marmousi II model available on http://www.agl.uh.edu/. The model, covering an area of 17 x 3.5km

decomposition, frequency-domain full-waveform modeling, full-waveform inversion, Giraud, hybrid direct-iterative solver, list, menu, parallel domain decomposition method, preconditioner, Reservoir Characterization, reservoir description and dynamics, scientific computing, seg las vegas, seismic modeling, seismic processing and interpretation, technical report tr pa, tomography, tool, Upstream Oil & Gas

SPE Disciplines:

We present a new stochastic tomography method for automatic background velocity estimation based on the local beam semblance of common-shot or commonreceiver gathers and the very fast simulated annealing (VFSA) global optimization method. The data space is the local beam semblance which is calculated using the local slant stacks for overlapping offset windows, i.e. beam windows, of the original common-shot or common-receiver gathers. On each beam semblance panel, the first coherency peak represents the first-arrival energy which can now be located with a particular ray parameter and traveltime and associated with the offset at the center of each beam window. The forward problem can be solved with an eikonal solver with/without ray tracing or beam method to find these first coherency peaks. Our inversion scheme uses VFSA to find the maximum a posteriori (MAP) solution and estimate the uncertainty by the application of Bayesian analysis to all the samples which are based on an optimal model parameterization. This integration of automatic local semblance evaluations instead of first-arrival picking, optimal model parameterization estimation and fast ray tracing or beam forward modeling method through VFSA makes our stochastic tomography robust, efficient and accurate.

analysis, Artificial Intelligence, automatic background velocity estimation, beam, beam semblance, function, inversion, local slant stack, method, model, optimal model parameterization, optimization problem, parameterization, position, ray, Reservoir Characterization, reservoir description and dynamics, seismic processing and interpretation, semblance, tomography, traveltime, Traveltime Tomography, Upstream Oil & Gas, VFSA

SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)

Technology: Information Technology > Artificial Intelligence > Representation & Reasoning > Optimization (1.00)

Zhou, Chaoguang (Petroleum Geo- Services) | Martínez, Jaime Ramos (Petroleum Geo- Services) | Lin, Sonny (Petroleum Geo- Services) | Jiao, Junru (Petroleum Geo- Services) | Dahl, Sverre Brandsberg (Petroleum Geo- Services)

Tomography has been widely employed for velocity model building. The typical work flow starts with the migration of an initial velocity model. This is followed by picking residual moveouts and then updating the velocity through tomography. The migration process provides common image gathers and a stack. At the tomography stage, a ray tracer is used to trace specular rays from the image points to the surface to set up the system of linear equations for the tomographic inversion by linking valid ray pairs to their corresponding residuals. For narrow azimuth (NAZ) surveys, searching for valid ray pairs is usually limited to a narrow azimuth band. Since neither the gathers nor the stack contain acquisition geometry information, the selected specular ray pairs may not reflect the true ray paths, resulting in inaccurate rays being used in the inversion process. In addition to the problem of "which rays to choose", we also have the problem of "how many rays to choose". These problems are even more difficult to handle with acquisition configurations other than NAZ, such as the wide azimuth towed-streamer (WATS) surveys, multi-azimuth (MAZ) surveys, and ocean bottom cable (OBC) surveys. To overcome these problems, we propose a tomography method that incorporates the acquisition geometry information and uses vector offsets to account for both offsets and azimuths. To address the ill-posed nature of the system of equations, we developed an anisotropic Laplacian regularization operator that allows different smoothing along different directions. We validate the method with tests on both synthetic and field data with a WATS geometry.

acquisition, acquisition geometry information, anisotropic regularization, building, direction, gather, geometry, information, migration, model, pair, ray, regularization, Reservoir Characterization, reservoir description and dynamics, residual moveout, seismic processing and interpretation, specular, survey, tomography, true geometry tomography, Upstream Oil & Gas

SPE Disciplines: Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)

**Summary**

Wide azimuth towed streamer surveys (WATS) have recently proven quite successful at improving illumination and attenuating multiple energy in difficult subsalt imaging environments. However, they present new challenges in terms of survey design, acquisition and processing methodology and operations. In particular, the sheer volume of data acquired requires pragmatic approaches to data processing. A 2007 deepwater Gulf of Mexico WATS survey of exploration scale (10,000 km2) illustrates these challenges and demonstrates the need for increased fold and cross-line offset.

acquisition, crystal, exploration-scale wide azimuth towed, gather, image, Imaging, radon, Reservoir Characterization, reservoir description and dynamics, seismic processing and interpretation, sequence, source, source line, source vessel, streamer, survey, tomography, towed streamer case study, Upstream Oil & Gas, vessel, WAT

Tomostatics using first breaks is a popular way to estimate near-surface statics due to the presence of low-velocity weathering zone. However, it is difficult to constrain the geometry of the base boundary of the weathering zone using first breaks, because the corresponding raypaths tend to be parallel with this boundary, traversing on top of the basement layer. We devise here a method of first-break deformable-layer tomostatics with constrains on the depth range of the base boundary of the weathering zone using reflections. Initial test of the method is conducted using a 2D field data set from western China. Comparison between the unconstrained and constrained tomographic models shows a similar geometry of the model layers, but the constrained portion of the base boundary of the weathering zone tends to have a sharper velocity contrast and laterally smoother than that of the unconstrained model. At many places greater than 10 ms difference exists in one-way vertical traveltimes over the weathering zone of the two models, meaning large difference in their static corrections.

base boundary, basement, boundary, constraint, correction, DLT model, geophysics, iteration, layer, model, reflection, Reservoir Characterization, reservoir description and dynamics, seg las vegas, seismic processing and interpretation, shallow reflection, shot, solution, Thickness, tomography, unconstrained dlt, Upstream Oil & Gas

The past couple of years have seen a tremendous increase in the acquisition of wide azimuth (WAZ) surveys that provide improved subsalt imaging. We have seen a step change improvement in image quality compared to conventional narrow azimuth (NAZ) surveys, even when using minimal processing and existing, conventional-survey velocity models. The improvement in image quality is taken to the next level when the wide and rich azimuth data are combined with other seismic and non-seismic measurements to build ever more highly constrained models, and then more accurately migrated with two-way wave-equation methods.

Over the past decade, the majority of deep water blocks in the Gulf of Mexico have been covered multiple times with seismic data from narrow-azimuth, towed-streamer acquisition (NAZ). In complex subsalt areas, each NAZ dataset provides unique subsurface illumination benefits. Multiple-azimuth data are now frequently integrated to provide extended subsurface coverage and for better imaging of complex subsalt structures. Multiple-azimuth seismic data, with shot and receiver locations covering a large portion of the two dimensional surface, presents a new challenge for deriving a single velocity model that satisfies both datasets.

Velocity variation with azimuth is observed in an orthogonal dual-azimuth streamer dataset in Deep Water Gulf of Mexico. This paper presents the benefit of tilted transversely isotropic (TTI) tomography to yield an anisotropy model that flattens gathers for all azimuths as well as improves focusing and spatial positioning of steeply-dipping salt flanks.

anisotropy, azimuth, basin, cig gather, dataset, dual azimuth, ew survey, gather, Imaging, las vegas, migration, model, Reservoir Characterization, reservoir description and dynamics, salt flank, seismic processing and interpretation, semblance, survey, tomography, TTI tomography, Upstream Oil & Gas

Seismic imaging in depth is limited by the accuracy of velocity model estimation. Slope tomography uses the slowness components and traveltimes of picked reflection or diffraction events for velocity model building. The unavoidable data incompleteness requires additional information to assure stability to inversion. One natural constraint for ray based tomography is a smooth velocity model. We propose a new, reflectionangle- based kind of smoothness constraint as regularization in slope tomography and compare its effects to three other, more conventional constraints. The effect of these constraints are evaluated through comparison of the inverted velocity models as well as the corresponding migrated images. We find the smoothness constraints to have a distinct effect on the velocity model but a weaker effect on the migrated data. In numerical tests on synthetic data, the new constraint leads to geologically more consistent models.

Slope tomography is one of the many methods that try to determine a macrovelocity model for time or depth imaging. It uses slowness vector components to improve and stabilize the traveltime inversion. Slope tomography was initially proposed by Billette and Lambaré (1998) as a robust tomographic method for estimating velocity macro models from seismic reflection data. They had recognized the potential efficiency of traveltime tomography (Bishop et al., 1985; Farra and Madariaga, 1988) but also the difficulties associated with a highly interpretative picking. The selected events have to be tracked over a large extent of the pre-stack data cube, which is quite difficult for noisy or complex data. The idea is to use locally coherent events characterized by their slopes in the pre-stack data volume. Such events can be interpreted as pairs of ray segments and provide independent information about the velocity model.

However, the data for slope tomography are incomplete (Bishop et al., 1985). This causes depth and velocity ambiguities that depend strongly on the size of the acquisition aperture (Bube et al., 2005). Therefore, stability and convergence can only be achieved if additional information is prescribed. This additional information contains desirable properties for the solution, reducing ambiguity (Menke, 1989). It can be shown that stability is obtained only if we try to determine a smooth model of the subsurface (Delprat-Jannaud and Lailly, 1992, 1993). Moreover, for ray based inversion, smoothness is a requirement, because rough models cause the forward problem to break down during linear iterations. The use of combined smoothness constraints enables an interpretation-oriented inversion while keeping solutions consistent with the data.

We investigate the effect of different kinds of smoothness constraints in slope tomography, prescribing lateral, vertical and isotropic smoothing constraints in different combinations. Moreover, we propose a structurally motivated smoothing constraint in the direction of a potential reflector. This regularization is based on information that is contained in the data, in contrast to standard regularizations that impose global smoothness constraints. We test the different regularizations on the Marmousoft data set (Billette et al., 2003).

Slope tomography differs from conventional reflection tomography by the data that are used for the inversion (Billette et al., 2003).

Billette, constraint, coverage, difference, direction, gradient, image, information, inversion, model, reflection, reflector, regularization, Reservoir Characterization, reservoir description and dynamics, seg las vegas, seismic processing and interpretation, slope tomography, smoothness constraint, tomography, traveltime, Upstream Oil & Gas

Checkshot survey and sonic measurement are used to pursue perfect seismic-well tie. The prime purpose of these in-situ surveys is to find a time-depth curve that matches best with velocity model.

It is widely believed that sonic wave always travels faster than seismic wave based on the dispersive effect (Wuenschel, 1965), so travel time at any depth measured by checkshot should be greater than sonic log integrated time. However, some observations show opposite results. Figure 1 displays a real well log survey. The right curve shows the result of subtracting checkshot travel time (left) by sonic integrated time (middle). The negative result means seismic wave travels faster than sonic wave. Such observation is supposed to be caused by heterogeneity effect of checkshot survey, such as a horizontal variant velocity formation. To resolve the horizontal variant velocity in such a narrow space, cell tomography method (Stork and Clayton, 1991) is applied to derive 2D velocity model. The dispersion effect is ignored in this study.

The ray tracing approach (Stork and Clayton, 1992) is used to model the checkshot survey to detect the influence of heterogeneity on the travel time. Figure 2(a) display a pseudo velocity model with the velocities increasing steadily with depth.

Checkshot measurements are modeled by shooting on the surface with offset as 50m and the downgoing direct wave. Figure 2(a) shows a synthetic velocity model and ray paths. As shown in 2(a) , ray paths always bend into curves instead of straight line because of depth variant velocities.

Ray paths in Figure 2(a) model the checkshot survey by ray tracing method. Time-depth curve calculated from integrated inverse vertical velocity (modeling the sonic measurement) is shown in black curve in Figure 2(b) and time-depth curve from ray tracing is shown in yellow curve in Figure 2(b). Two curves appear very small deviation that means horizontally homogeneous media does not cause much difference between checkshot and sonic measurement. Then lets go on to the real data. Figure 3(a) shows a real sonic log data; (b) is the layer velocity model expanded horizontally from the sonic data and the modeled ray path of checkshot survey through the formation; (c) blue curve is the time-depth curve from real checkshot data and yellow curve is modeled time-depth curve from the ray path in (b). As shown in the Figure 3(c), modeled travel time is larger than real measurement at deeper formation that demonstrates the presence of heterogeneity at deeper part. I will derive the 2D horizontally variant velocity from the checkshot survey based on the sonic measurement by means of tomography.

Cell tomography is kind of traveltime tomography (Stork and Clayton, 1991). By this means, the velocity field is parameterized as an effective continuum of desired accuracy. This parameterization places no inherent restrictions on the structure the velocity field can take on. Three common methods for representing a continuum are with two-dimensional (2-D) splines, wavenumbers, or a grid of cells. I here use cells model.

borehole imaging, cell, checkshot, checkshot survey, checkshot-sonic microscale tomography, deviation, formation evaluation, geophysics, model, production control, production monitoring, ray, ray path, raypath, Reservoir Characterization, reservoir description and dynamics, Reservoir Surveillance, seg las vegas, slowness, time-depth curve, tomography, traveltime, Upstream Oil & Gas, wellbore seismic

Thank you!