A method of seismic shot-record migration includes the steps of generating seismic or acoustic waves into an earth formation from one or more sources with the sources being spaced some finite distance from each other. Next, one or more spaced receivers receive a seismic signal after the signal reflects or diffracts off of a subterranean feature. Next, a source location and a receiver location is arbitrarily selected. Finally, input data is mapped or migrated according to one of two equations, or both equations, to produce output data. The output data is then suitable for further processing by other seismic analysis techniques.

System and method of seismic shot-record migration

Among the reasons for considering optional seismic processes such as dip moveout (DMO) or prestack migration is the fact that two reflections with the same arrival time may require different stacking velocities in order to produce an acceptable image. For example, inline dip tends to increase the required stacking velocity, and DMO can be applied to correct this effect. Crossline dip has no direct effect on stacking velocity, but, because average velocity tends to increase with depth, a dipping reflection broadside to a seismic line will tend to require a lower stacking velocity than an in-plane reflection with the same time of arrival. This problem is not addressed by DMO, but it can be handled by what I call "crossline prestack migration."

Kinematics of crossline prestack migration

The focus of this project is direct detection of DNAPLs, specifically chlorinated solvents, via material property estimation from multi-fold surface ground-penetrating radar (GPR) data. We combine state-of-the-art GPR processing methodology with quantitative attribute analysis and material property estimation to determine the location and extent of residual and/or pooled DNAPL in both the vadose and saturated zones. An important byproduct of our research is state-of-the-art imaging which allows us to pinpoint attribute anomalies, characterize stratigraphy, identify fracture zones, and locate buried objects.

/pdf/material-property-estimation-for-direct-detection-of-dnapl-1q8c7kd0l2.pdf

Material Property Estimation for Direct Detection of DNAPL using Integrated Ground-Penetrating Radar Velocity, Imaging and Attribute Analysis

The two-dimensional (2D) cross-hole seismic computed tomography (CT) imaging acquisition method has the potential to characterize the target zone optimally compared to surface seismic surveys. It has wide applications in oil and gas exploration, engineering geology, etc. Limited to 2D hole velocity profiling, this method cannot acquire three-dimensional (3D) information on lateral geological structures outside the profile. Additionally, the sensor data received by cross-hole seismic exploration constitute responses from geological bodies in 3D space and are potentially affected by objects outside the well profiles, distorting the imaging results and geological interpretation. This paper proposes a 3D cross-hole acoustic wave reverse-time migration imaging method to capture 3D cross-hole geological structures using sensor settings in multi-cross-hole seismic research. Based on the analysis of resulting 3D cross-hole images under varying sensor settings, optimizing the observation system can aid in the cost-efficient obtainment of the 3D underground structure distribution. To verify this method’s effectiveness on 3D cross-hole structure imaging, numerical simulations were conducted on four typical geological models regarding layers, local high-velocity zones, large dip angles, and faults. The results verify the model’s superiority in providing more reliable and accurate 3D geological information for cross-hole seismic exploration, presenting a theoretical basis for processing and interpreting cross-hole data.

3D Reverse-Time Migration Imaging for Multiple Cross-Hole Research and Multiple Sensor Settings of Cross-Hole Seismic Exploration

In a viscoacoustic medium, intrinsic attenuation causes seismic wavefields to attenuate in amplitude and become dispersed in phase, leading to distorted structural imaging and inaccurate migrated amplitudes. To address this problem, viscoacoustic RTMs correct for dispersion and amplitude attenuation effects in wavefield propagation in both forward and backward directions. To provide a parallel alternative approach, we solve the time fractional derivative viscoacoustic wave equation within the depth domain and establish a Q-compensated wavefield depth extrapolation scheme to compensate for viscoacoustic effects during recursive wavefield depth extrapolation. This approach decouples the amplitude attenuation and phase dispersion effects from the viscoacoustic vertical wavenumber. To suppress high wavenumber components and address the problem of amplitude exponential growth during wavefield depth extrapolation, we limit the imaginary part of the vertical wavenumber in the frequency wavenumber domain and employ an adaptive stabilization solution. Numerical experiments of impulse responses in an isotropic medium demonstrate that our proposed scheme can observe wavefields with amplitude attenuation and phase dispersion effects in comparison to wavefields of the acoustic medium. We also demonstrate the capability of our proposed scheme in recovering imaging amplitudes through a variety of numerical experiments, including imaging of three-layer, Marmousi, and BP gas reservoir models. The results show that our proposed scheme can recover amplitude attenuation and phase dispersion effects correctly compared with the results of acoustic migration. We also use marine seismic data featuring natural gas hydrates to show that our proposed Q-compensated scheme can generate an enhanced imaging result, especially for the bottom simulating reflectors (BSRs), compared with the conventional imaging algorithm without considering Q-compensation.

Q-compensated wavefield depth extrapolation based migration using a viscoacoustic wave equation

In two-way wave equation depth migration by either time-extrapolation or depth-extrapolation, an efficient wavefield separation scheme (to separate two-way wavefields to their one-way counterparts: down- and up-going waves) is typically required for high quality imaging. For a depth extrapolation scheme, this wavefield separation is conventionally accomplished by utilizing two wavefields, the pressure p and its derivative p z. However, that wavefield separation scheme presents a significant challenge in both the accuracy and the computational cost for two-way wave equation based depth migration. To address this challenge, we propose a new wavefield separation algorithm for two-way wave equation depth extrapolation scheme, in which a new pressure wavefield q is introduced to replace the pressure derivative wavefield p z in boundary conditions and propagator of the conventional formulation. Since the pressure wavefield p represents sum of down- and up-going waves, while the pressure wavefield q denotes difference of down- and up-going waves, wavefield separation in the new algorithm becomes very simple and efficient - a summation and subtraction operation only at each depth step. The performance of our proposed algorithm for wavefield separation is verified and demonstrated by numerical experiments conducted on a number of synthetic models. These experiments include examples of wavefield separation of both the source and the receiver, migration tests on the 2D SEG/EAGE salt model (regarding one-way vs. two-way depth extrapolation, and comparison of evanescent wave suppression methods), and turning wave migration tests on three complex velocity models: the step model, the salt dome model, and the BP salt model.

Efficient wavefield separation by reformulation of two-way wave-equation depth-extrapolation scheme

Conventional two‐pass 3-D time migration is exactly equivalent to full 3-D time migration in a homogeneous medium. For vertically inhomogeneous media representing typical earth velocities, however, conventional two‐pass 3-D migration fails to correctly image dips beyond about 45 degrees. This failure is the result of an inherent velocity error incurred during the first pass of a two‐pass 3-D migration. For a vertically inhomogeneous medium, the theory of residual migration can be combined with the results for homogeneous media to derive a series of successive two‐pass migration stages which are equivalent to a full 3-D migration. Each stage of this generalized two‐pass 3-D migration is implemented using an appropriate constant migration velocity. In practice, the required number of two‐pass stages can be reduced to a computationally manageable few; and the I/O can be reduced by one‐third to one‐half of that required using a straightforward application of repeated two‐pass migrations. This procedure allows...

Generalized two‐pass three‐dimensional migration for imaging steep dips in vertically inhomogeneous media

Three-dimensional filter operations, such as migration, dip filtering, and dip enhancement can require large computational resources and programming efforts. For many such processes, the 3-D filtering can be accomplished efficiently by 1) decomposing the data into its true-dip components, 2) applying 2-D (or even 1-D) filter operations, and 3) reconstructing the 3-D volume from the filtered true-dip components. In this paper, we show how to efficiently do true-dip component decomposition by applying Radon transforms on time slices. The result of applying this technique to a 3-D data volume is a series of radial sections, where each section contains only true-dip information. To spatially sample the volume sufficiently, the number of radial lines is typically on the order of the sum of the number of in-lines and cross-lines. Any 2-D standard filtering technique, such as time migration, dip filtering, dip enhancement, and dip dependent deconvolution can be applied to each radial section without suffering 3-D dip-azimuth effects. An inverse Radon transform on time slices reconstructs (back-projects) the truedip 2-D components from radial lines to its corresponding 3-D structure.

Efficient 3‐D filtering using projected 2‐D true‐dip Sections

In this paper we develop a new approach for seismic imaging which can accomplish exact 2-D prestack migration in a vertically inhomogeneous medium. The elegance of this method is that it avoids the usual timeconsuming procedures of recursive wave field extrapolation or ray tracing. The new migration algorithm is based on using double pz transforms. The double p-z transform defined in the midpointoffset-time domain is a natural extension of the single p-t transform. 2-D prestack migration for vertically inhomogeneous media can be exactly accomplished by a forward plus a modified inverse double p-z transform. The modified inverse p-T transform involves a scaling of the intercept ime We refer to the new method as a nonrecursive p-z prestack migration. Although the double p-t transforms can be implemented in either the wavenumber-frequency or space-time domain, the modified inverse double p-T transform is best performed in the space-time domain due to its time-variant characteristics. Since the final calculation is implemented point by point in the spacetimedomain, this method easily accommodates moderate lateral velocity variation. Moreover, the migration result can be calculated at any selected trace and timesample making it suitable for efficient migration velocity analysis. The migration algorithm is tested on synthetic data to demonstrate its accuracy and performance.

Nonrecursive Approach For Exact 2-D Prestack Migration In Vertically Inhomogeneous Media Via Double P-Tau Transforms

Exact Two-Pass Full Dip (> 90°) 3-D Migration For Vertically Inhomogeneous Media

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