This algorithm, which is kirchhoffbased, uses a common velocity model to migrate the two data sets to a single output grid, eliminating the need for splicing the vsp section into the surface seismic image. Use of prestack depth migration for improving the accuracy. Panorama technologies chapter 6 prestacktimeanddepth migration prestackmigrationalgorithmsarerelativelysimplevariantsofthepoststack methodologies. A general formulation of prestack depth migration based on imaging mapping incident and scattered wave. The simple answer to your question is computer speed migration is a relatively computationally expensive process, and while kirchhoff prestack migration techniques are mathematically pretty old, the sheer brute computer power to make them practical on 3d datasets didnt really emerge until the first largescale parallel linux clusters. Its effectiveness can become limited, however, when complex velocity structure causes multipathing of seismic energy. Summary multioffset vsp and surface seismic data from the rocky mountain foothills of southern alberta, canada, has been used to. Anisotropic prestack depth migration cseg recorder. In previous editions, the emphasis has been on migration techniques based on the oneway wave equations. Prestack kirchhoff depth migration of shallow seismic data. Migration parameters such as aperture, dip limits and antialiasing. The algorithm is implemented as a kirchhofftype migration, in which the migrated image is generated by weighted summation along diffraction surfaces through the shot record section.
Prestack depth migration psdm is typically aimed at improv ing image quality in areas of complex geology, such as below salt. Exploring and producing unconventional reservoirs generates different challenges. Specifically, by migrating each of the nmo and dmocorrected common. Pdf imaging conditions for prestack reversetime migration. Parallel 3d prestack depth migration using recursive. Poststack depth migration is often performed for reasons of economy but prestack depth migration is almost always required since it is almost impossible to define an accurate velocity model using purely poststack processing. Raybased prestack depth migration for orthorhombic media. Prestack depth migration an ultimate aspiration for.
Prestack depth migration earth signal processing ltd. Lawton and 2scott cheadle 1university of calgary, 2veritas dgc inc. 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. Unmigrated is wrong because there are inherent velocity assumptions which makes the image incorrect. Among all other methods for seismic prestack depth migration, grt is unique by. The motivation behind this study was to locate an underground building buried in a waste disposal. Introduction to the traveltime tomography and prestack migration for. The results show fault lines and saltbody, but some geological interfaces of the lower parts of saltbody is uncelear. Seismic prestackdepth migration grt fraunhofer itwm. Practical aspects of prestack depth migration with finite. In addition to velocity model workflows, it should be noted. The robust alternative in practice is to apply nmo and dmo corrections followed by poststack time migration. Migration in our approach, prestack depth migration may be decomposed into the following steps claerbout, 1971. Our implementation images arrivals that propagate at 90 and higher angles as turning waves.
Finally, the velocity model from the inversion was used to perform a prestack depth migration on the seismic dataset after carrying out the noise suppression procedures. The advantage and significance of prestack migration cseg. Prestack depth migration an ultimate aspiration for subsurface imaging in geologically complex area. An alternative residualcurvature velocity updating method. Most current trueamplitude migrations correct only for geometric spreading. Migration can be applied to the unstacked data socalled prestack migration so that the data need not be reduced to an approximation to zero offset before migration. We had introduced a concept of flexi depth iterations while depth migrating data in parallel imaging space. Implementation of kirchhoff prestack depth migration on gpu. Prestack depth migration presdm is a robust method for obtaining proper image of complex subsurface.
The traveltime tomography allows to build a velocity model from the first arrival traveltimes. It is a fast and accurate wave equation prestack depth migration that can provide users with results the next day. This paper presents an overview of the results obtained from a 3d prestack depth migration of the is0893d data set. Prestack migration by equivalent offsets and csp gathers. Therefore, to get the best possible image, as predicated by the data set in figures 8. Marc langlois abstract we have designed and implemented a parallel 3d prestack depth migration algorithm. Imaging conditions for prestack reversetime migration article pdf available in geophysics 733 may 2008 with 546 reads how we measure reads. Introduction to the traveltime tomography and prestack. Integrated prestack depth migration of vsp and surface seismic data in order to test the new, integrated prestack depth migration algorithm, a numerical model was developed based on the interpretation of the field data.
Seismic migration download ebook pdf, epub, tuebl, mobi. Details of the model at the target level are shown in figure 3a. A validity check is performed on each computed a i for. It can be divided ray and wave equationbased method. Finitedifference, prestack, depth migrations offers significant improvements over kirchhoff methods in imaging near or under salt structures. Of course, we used the actual migration velocities to perform the prestack depth migration but, in general, we must estimate those velocities somehow. Depth migration, tomography, velocity model, depth conversion. Seismic prestackdepth migration grt the project on g eneralized r adon t ransform grt depth migration excellently demonstrates how the unified competence in the fields of geophysics, mathematics, and informatics of the department hpc could be used for the successful development of a tailormade product according to clients particular. The results of 3d prestack depth migration at xline 1540 m, 5320 m, 7540 m, and from top to bottom8640 m. The multireceiver extension of this formula is suitable for an automated prestack amplitudeversusangle ava elastic inversion of. Sourcereceiver prestack depth migration using dreamlets.
From this image, correlation of different events with depth values can be made. Performing prestack depth migration shown in figure lc has, in addition to clearing up the small amount of residual noise present on the time migrated section, solved the depth conversion problem. In our previous work, an efficient parallel poststack and prestack 3d kirchhoff depth migration algorithm had been successfully demonstrated on current class of multicore systems rastogi et al. Apr 17, 2001 kirchhoff migration is the most popular method of threedimensional prestack depth migration because of its flexibility and efficiency. The unconformity, which is commonly occur in prestack time migration pstm section, can be removed by providing an accurate velocity model. The processing sequence of the prestack migration is simplified significantly as compared to standard common cmp data processing. Set the correct plot settings both for the migrated section and the tomogram and save them within the fileheader. Prestack depth migration earth signal maintains an ongoing partnership with data modelling inc. Prestack, and poststack migration refer to different points in the processing flow at which you decided to migrate the data. Compared to a cpu only version of the same algorithm, thenew approach delivers a significantly greater efficiency.
An alternative residualcurvature velocity updating method for prestack depth migration hongbo zhou, jiuying guo and jerry young, veritas dgc inc. Wu, 2007, imaging steep salt flanks by superwide angle oneway method, 77th annual international meeting, seg, expanded abstracts. We present a new prestack depthmigration method that uses the framework of reversetime migration to compensate for. Sourcereceiver prestack depth migration using dreamlets 2 cos ij j i j j bt b t t t t 2 and 1 i 2 j i t. 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. Generalized radon transform grt depth migration excellently demonstrates how the unified competence in the fields of geophysics, mathematics, and informatics of the department hpc could be used for the successful development of a tailormade product according to clients particular needs. Simultaneous anisotropic prestack depth migration of ps. Many competing algorithms have been proposed by various authors. Prestack depth migration velocity model building in complex carpathians geology krzysztof karol sliz agh university of science and technology faculty of geology, geophysics and environmental protection al. The migration step can, however, be moved up to precede cmp stacking. Kirchhoff prestack depth and time migration schlumberger. Prestack migration by equivalent offsets crewes research report volume 7 1995 231 prestack migration by equivalent offsets and csp gathers.
Promax depthcharge velocity modeling and depth imaging. 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. The author assumed that correct model can be built when the lateral resolution of. Integrated prestack depth migration of vsp and surface. Kirchhoff migration is the most popular method of threedimensional prestack depth migration because of its flexibility and efficiency.
Calgary, alberta, canada t2p 5e9 introduction in western canada there is only a small percentage of seismic data processed with prestack migration. Parallel migration research crewes research report s volume 14 2002 1 parallel 3d prestack depth migration using recursive kirchhoff extrapolation hugh d. That is, an energy source is used to generate a pulse of acoustic energy and direct it into the ground. In this paper, 3d parallel shotgather prestack depth migration with hybrid is developed and implemented. Historically the development of time migration proceeded in advance of depth migration mainly because of computer technology. Mickiewicza 30, 30059 krakow, poland geofizyka krakow ltd. 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. For this purpose you must perform the following steps. A commonshot prestack depth migration is assumed since it is the most natural con.
The result of the psdm overlaid with the velocity field is shown in figure 3. Image quality is further improved by the ability to honor both vertical and tilted transverse isotropy vti and tti. Foltinek abstract a method of prestack time migration is presented that is simpler, faster, and. The goal of prestack depth migration is to reconstruct an image of the subsurface with the highest possible resolution. Part i true amplitude propagator and seismic migration imaging.
This is the third edition of part a of seismic migration now widely recognized as an authoritative, thorough treatment of seismic migration theory and methods. Pdf psdm is increasingly becoming rule rather than exception in near surface seismic imaging when the goal is to get detailed subsurface. Prestack depth migration from topography landmark solutions. As stated early in the chapter, the rigorous solution to the problem of conflicting dips with different stacking velocities is prestack time migration. The image quality of the finitedifference scheme has been investigated and suggested improvements are discussed. If the physical sample increment is 5 m or 15 ft, and if we. If the data is read in properly then note the correct and reasonable values.
Raypath distortions can be so severe in areas of complex velocity variations that conventional poststack processing often. Feb 14, 2014 the simple answer to your question is computer speed migration is a relatively computationally expensive process, and while kirchhoff prestack migration techniques are mathematically pretty old, the sheer brute computer power to make them practical on 3d datasets didnt really emerge until the first largescale parallel linux clusters. This exhibits the flexibility of the algorithm in terms of the number of iterations which are decided depending upon the data to be migrated and available node memory. Local image matrix and local ava, 73rd annual international meeting, seg, expanded abstracts, 973.
Similarly, prestack time migration can be conceptualized either by way of semielliptical superposition using equation or diffraction summation over the traveltime surface described by equation. Prestack depth migration for seismic reflection data is commonly used tool for imaging complex geological structures such as salt domes, faults, thrust belts, and stratigraphic structures. Data preparation for prestack depth migration crewes. Our results show that incorporation of higher order anisotropy under certain geology improves migration of wide azimuth waz acquisition data, and produces focused migration images to be used in. Hence, migration is carried out in 8 depth iterations with 25 as ttl for poststack, and in 14 depth iterations with 14 as ttl for prestack. Summary residualcurvature analysis of prestack depth migrated common image gathers cigs is widely used for updating the whole velocity model in areas of complex geology.
Prestack gaussianbeam depth migration geoscienceworld. In the foothills, prestack depth migration is interpretive. The traveltime surface, which is shown in figure 5. Prestack time migration and post stack depth migration. Prestack depth migration is essential to seismic reflection imaging in areas where steeply dipping structures or extreme lateral velocity variations exist in the subsurface, such as along the flanks of salt domes or in strikeslip fault zones. Part i true amplitude propagator and seismic migration.
We present a new prestack depth migration method that uses the framework of reversetime migration to compensate for. Analysis on presatck depth migration psdm has been applied to nirmala field seismic data which has complex structure and strong lateral velocity variation. Nevertheless, the real bottleneck in 3d prestack processes is the sheer amount of input and output data. The authors have implemented a finitedifference prestack depth migration algorithm for use on massively parallel computers which is discussed. 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.
This book also obtains a formulated forward modeling and migration theory by introducing the. Phase shift plus interpolation pspi algorithm is a useful tool to directly solve a wave equation and the results have natural properties of the wave equation. Prestack depth migration of synthetic data set using the known velocity model. The data were first migrated isotropically, with a velocity model built using the constant fast velocity of the thrust sheet and its actual spatial location, for the migration. The improvement in imaging of steep reflectors by this approach, however, is bought at the price of a great increase in the amount of computation required for the migration.
Prestack depth migration is a useful tool for understanding complex structures in the north sea and elsewhere around the. Prestack time and depth migration panorama technologies. 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. Model velocities were assigned from sonic logs from the vsp well. Following the drilling of the paktoa c60 well, applied geophysical services used their proprietary beam algorithm to image very steeply. 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. This process is necessary to overcome the limitations of geophysical methods imposed by areas of complex geology. A mixture of target lines and full data cubes were processed in this way. An actual production run with field data reveals the extent of the improvements. This unique partnership allows dmi to remotely run their proprietary velocity modelling and migration.
Note that prestack depth migration produces an image that is free of the distortions observed on the image produced by poststack depth migration. Trueamplitude prestack depth migration request pdf. Pdf prestack depth migration of ultrashallow seismic data. Simultaneous anisotropic prestack depth migration crewes research report s volume 12 2000 depth image, which may contain more information and better resolution than either section alone. What then is an appropriate algorithm for 3d prestack depth migration kirchhoffsummation, finitedifference, or frequencywavenumber. The primary difference lies not in the mathematical theory but in.
Converting prestack gathers between segy and aaspi. This involves generating travel times through the model and subsequent summation of contributing input data to the specified output locations. Prestack depth migration in angledomain using beamlet decomposition. Prestack migration algorithms are relatively simple variants of the poststack methodologies. Migrating the data, moves reflections to their correct spots. Seismic migration based on ray methods such as kirchhoff gray and may,1994. This integrated migration can then be used for a new pass of migration velocity analysis to determine a better depthvelocity model for remigration of both. Wu, 2007, imaging steep salt flanks by superwide angle oneway method, 77th annual international meeting, seg, expanded abstracts, 22652269. Prestack kirchhoff time migration of 3d coal seismic data. We demonstrate the capability of our algorithm for orthorhombic anisotropy using synthetic and real data examples from the gulf of mexico. Tests of a kirchoff prestack depth migration psdm algorithm prior to drilling had resulted in no significant improvement.
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