Summary multioffset vsp and surface seismic data from the rocky mountain foothills of southern alberta, canada, has been used to obtain the. Prestack depth migration an ultimate aspiration for subsurface imaging in geologically complex area. Prestack depth migration for easy unconventional plays. Optimization methods for prestack and poststack migration. Improved imaging through anisotropic depth migration and. Use of prestack depth migration for improving the accuracy. Kessler serves as the president of seismiccity since its incorporation in early 2000. Why prestack depth migration is worth its salt offshore. Introduction prestack depth migration psdm is typically aimed at improv ing image quality in areas of complex geology, such as below salt or faults, and has traditionally been applied only in the presence of such challenges. Integrated prestack depth migration of vsp and surface. First off, all reflection seismic data is recorded in time whether onshore or offshore.
Each shot record in a physical model data set is inverted separately with a common shot, prestack inversion routine with a laterally and depth. Prestack depth migration by 3d reflection tomography in the north sea. Gray2, and yu zhang3 abstract prestack depth migration is the most glamorous step of seismic processing because it transforms mere data into an image, and that image is considered to be an accurate structuraldescriptionoftheearth. Pdf prestack depth migration for 2d crooked line surveys. Prestack depth migration of primary and surfacerelated. Panorama technologies chapter 6 prestacktimeanddepth migration prestackmigrationalgorithmsarerelativelysimplevariantsofthepoststack methodologies. Kirchhoff prestack depth migration ion geophysical. Prestack depth migration of shot profiles by downward continuation is a practical imaging algorithm that is especially costeffective for sparseshot wideazimuth geometries. Through the use of abundant checkshot velocity information 539 checkshots and anisotropic parameter estimation, wellcalibrated velocities could be used for migration. Seismic migration is the process by which seismic events are geometrically relocated in either space or time to the location the event occurred in the subsurface rather than the location that it was recorded at the surface, thereby creating a more accurate image of the subsurface. In time migration, the major impact of velocity is to focus or defocus reflectors and diffractors with some lateral movements. Its effectiveness can become limited, however, when complex velocity structure causes multipathing of seismic energy.
Prestack depth migration by 3d tomographic inversion of reflected and refracted arrivals. The advantage and significance of prestack migration cseg. In prestack migration analysis, velocities are computed in order to optimize some property such as focusing, or the offset consistency of depth migrations. Lawton and 2scott cheadle 1university of calgary, 2veritas dgc inc. Normal moveout nmo and stacking of csp gathers is performed to complete the prestack migration process. Nevertheless, the real bottleneck in 3d prestack processes is the sheer amount of input and output data. Migration on 3d seismic data using kirchhoff prestack depth migration kirchhoff psdm method at nirmala field north west java basin analysis on presatck depth migration psdm has been applied to nirmala field seismic data which has complex structure and strong lateral velocity variation. Kirchhoff depth migration in the sense that the amplitude of the imaged reflections is proportional to the reflection coefficient. An overview of depth imaging in exploration geophysics john etgen1, samuel h. Geiger summary the goal of prestack depth migration is to reconstruct an image of the subsurface with the highest possible resolution. Once data are spatially regularized so that the resulting prestack data have uniform fold of coverage and have been corrected for sourcereceiver azimuth, then, in principle, any of the three categories of migration algorithms kirchhoffsummation, finitedifference, or frequencywavenumber, can be used to perform 3d prestack depth migration. In its simplest form, then, seismic migration is the process that converts information as a function of recording time to features in subsurface depth. As expected, due to the large velocity contrast at the steep top salt interface, the time migration is incapable of producing a.
He started his industrial career as a research geophysicist developing algorithms for velocity estimation, model building and prestack depth migration and held a senior research scientist position for landmarkita 19911994 and a. Rather than simply stretching the vertical axes of. Prestack kirchho time migration for complex media tariq alkhalifah1 keywords. Many competing algorithms have been proposed by various authors. However, the more complex the geology, the more difficult it is to find an accurate velocity model zelt et al. It gives an overview on the goals and techniques utilized in imaging of seismic data. Prestack time migration and post stack depth migration. In depth migration, these features are also moved laterally and vertically. Depth imaging using primary and multiple reflections dipmr involves decomposing the datainto upgoing and downgoing wave constituents, followed by downward extrapolation. To accomplish these goals, all available well information was used to calibrate the seismic velocity model from prior. A method of prestack time migration based on the principles of prestack kirchhoff time migration that can be applied to both 2d and 3d data. These algorithms map the recorded seismic reflection energy from a surface location to a subsurface. The final velocity model, constrained by seismic data, also.
B prestack depth migration compared to the prestack time migration, the final prestack depth migrated section showed a significantly enhanced definition of the main structures, as well as improved continuity of the reflectors. The sdgs central reference to migration is made in target 10. Kirchhoff migration is the most popular method of threedimensional prestack depth migration because of its flexibility and efficiency. Depth migration, on the other hand, images these two reflectors, accurately, if the velocity depth model input to depth migration is the true model as in the case of figure 8. Calgary, alberta, canada t2p 5e9 introduction in western canada there is only a small percentage of seismic data processed with prestack migration. Management david kessler, president, seismiccity, inc dr. Data preparation for prestack migration crewes research report volume 16 2004 1 data preparation for prestack depth migration hugh d.
An overview of depth imaging in exploration geophysics. Pdf offset and angledomain common imagepoint gathers. Common scatter point csp gathers are created as an intermediate step for each output migrated trace. Enhanced anisotropic model building methodology and. To solve this problem and improve the quality of imaging in complicated media, we propose a prestack depth migration operator with coefficient optimized paraxial wave equation on the common shot gathers. Prestack migration reservoir characterization schlumberger. Overview on the fundamentals of imaging cseg recorder. Attributes assisted seismic interpretation in prestack. Pdf prestack depth migration by 3d tomographic inversion. Seismic migration is a process to turn the reflectors on the stack image into true geological interface. We present a prestack depth migration method that allows primary and multiple reflections to be imaged simultaneously. This analysis is in the context of building velocity depth models for 3d prestack depth migration presdm, but i do not address the specific limitations of individual migration algorithms, other than to mention some scalelength assumptions made by raybased methods. Introduction to the traveltime tomography and prestack migration for boreholedata within reflexw in the following the use of the traveltime tomography and the prestack migration for different types of borehole data is described. Prestack gaussianbeam depth migration geoscienceworld.
Prestack depth migration velocity model 315 low resolution of stacking velocities, fast lateral velocity changes and sparse coverage of well information, strong influence of noise and steep horizons for estimated velocities, problems with assigning a single gradient function for a given zone. That is, an energy source is used to generate a pulse of acoustic energy and direct it into the ground. Whitmore and garing 1993 describe an ingenious plane wave prestack depth migration which uses the criterion that depth migrations should not depend on angles of plane wave sources. Dai and others published an adaptive phase shift and ssfpi method for prestack depth migration find, read and cite all the research you need on researchgate. Kirchhoff prestack depth and time migration the most widely used migration algorithm in the industry accommodate a range of geological settings and acquisition geometries with flexible, amplitudepreserving implementation. Although we used the true velocity depth model, time migration produced the incorrect image of the basesalt boundary and the subsalt region. The goals of this large scale project were accurate event placement and improved imaging of steep dips, salt boundaries, and subsalt events. The interpretation of offset as the displacement between the downwardpropagating shot wavefield and upwardpropagating receiver wavefield enables us to extract offsetdomain common. Until the migration step, seismic data are merely recorded traces of echoes, waves that have been reflected from anomalies in the subsurface. When one considers the milestones in the application of seismic methods to further oil and gas exploration over the last 20 years, one usually thinks first of the progression from 2d to 3d and now 4d timelapse seismic. The author assumed that correct model can be built when the lateral resolution of.
The migration algorithms presented are based in the gulf of mexico but are applicable throughout the world. Request pdf accelerating kirchhoff prestack depth migration on a gpu by overlapping ray tracing and imaging kirchhoffbased depth migration is in great demand for imaging at large scales and. Prestack depth migration an ultimate aspiration for. Accelerating kirchhoff prestack depth migration on a gpu. It is intended for those who are unfamiliar with seismic imaging or are not. Given that seismic data is bandlimited, the ideal response. Prestack crewes research report volume 2001 555 cos rms stk v v. Download as ppt, pdf, txt or read online from scribd.
Kirchhoff prestack depth and time migration schlumberger. Prestack depth migration has been an industrial imaging standard for decades, starting from the adoption of kirchhoff migration in the early nineties to the emergence of reversetime migration rtm in the late 2000s. The author assumed that correct model can be built when the lateral. Image quality is further improved by the ability to honor both vertical and tilted transverse isotropy vti and tti. Pdf on jan 1, 2003, hideo saito and others published prestack depth migration for 2d crooked line surveys find, read and cite all the research you need on researchgate. If the velocity model is inaccurate, depth migration may be inferior to time migration. Summary over the last decade, it is predominantly perceived that there have been significant evolutions in prestack depth imaging consisting of both velocity depth model building and. Introduction to the traveltime tomography and prestack. There are many methods used in industry to construct velocity models for prestack depth migration, including interval. It can be divided ray and wave equationbased method. The other key enhancement to the previous processing flow was the use of anisotropic prestack depth migration. The traveltime tomography allows to build a velocity model from the first arrival traveltimes.
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