A natural advantage of depth migration is that the output image is displayed in depth and therefore can directly be utilized for geologic interpretation. Raybased prestack depth migration for orthorhombic media. The impact of gradiometer technology on model driven seismic imaging, first results in the southern. Gravity gradients for derisking prestack depth migration, e. A sampling of depth gathers resulting from the migration in figure 15. Practical aspects of prestack depth migration with finite.
Note that the basal reflector is located in the correct depth location under the thrust sheet and the residual structure has been eliminated. Kirchhoff prestack depth and time migration schlumberger. Geiger summary the goal of prestack depth migration is to reconstruct an image of the subsurface with the highest possible resolution. We see that the amplitude balance and image quality have been improved. 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. Summary multioffset vsp and surface seismic data from the rocky mountain foothills of southern alberta, canada, has been used to. The theory of extrapolation of nonzerooffset wavefields is provided in wavefield extrapolation and migration, while the stationaryphase traveltime trajectory associated with nonzerooffset wave propagation is given in nonzerooffset traveltime equation. 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 velocity model building in complex carpathians geology krzysztof karol sliz agh university of science and technology faculty of geology, geophysics and environmental protection al. Analysis on presatck depth migration psdm has been applied to nirmala field seismic data which has complex structure and strong lateral velocity variation. We applied it to the 3 d segeage salt velocity model. The conventional approach using prestack time migration pstm and prestack depth migration psdm results in a strong reflection at the top of the shuaiba, but without details of internal structure within this 100 m thick layer. Prestack depth migration presdm is a robust method for obtaining proper image of complex subsurface. Migration can be carried out in prestack or poststack domain.
It is a fast and accurate wave equation prestack depth migration that can provide users with results the next day. An overview of depth imaging in exploration geophysics cgg. Marc langlois abstract we have designed and implemented a parallel 3d prestack depth migration algorithm. Our series of prestack depth migration algorithms are built to answer imaging requirements of any geological setting. Postdm2d 2d kirchoff poststack depth migration postdm3d 3d kirchoff poststack depth migration presdm prestack kirchhoff depth migration singlecpu psmig phaseshift migration with turning rays psmig25 2.
Given that seismic data is bandlimited, the ideal response. The author assumed that correct model can be built when the lateral resolution of. Migration in our approach, prestack depth migration may be decomposed into the following steps claerbout, 1971. How to optimize the obtaining the required ray travel time data is very important to the efficiency of parallel processing the prestack depth migration. Pdf from prestack migration to migration to zerooffset.
Resolving fault shadow problems in irian jaya indonesia. This diagram shows the difference between the raypaths for a common midpoint cmp from source to receiver for a flat layer green, and those for a dipping layer near and far o. An actual production run with field data reveals the extent of the improvements. The traveltime tomography allows to build a velocity model from the first arrival traveltimes. Reverse time imaging of groundpenetrating radar and sh. Parsimonious 3d prestack kirchhoff depthm igration.
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. Qcompensation in complex media s raybased and wavefield. The authors have implemented a finitedifference prestack depth migration algorithm for use on massively parallel computers which is discussed. Deriving and refining the velocity model is an iterative process, requiring numerous preliminary migrations and analysis cycles. We conducted a numerical model test to verify prestack depth migration by the 3d pspi. What then is an appropriate algorithm for 3d prestack depth migration kirchhoffsummation, finitedifference, or frequencywavenumber. Current anisotropic imaging techniques routinely handle wave propagation in transverse isotropic ti media, either with a vertical symmetry axis. Finitedifference, prestack, depth migrations offers significant improvements over kirchhoff methods in imaging near or under salt structures. Depth migration compensates for ray bending, lateral velocity pullups and structure. Parallel migration research crewes research report s volume 14 2002 1 parallel 3d prestack depth migration using recursive kirchhoff extrapolation hugh d.
Prestack migration is always superior if there is dip involved. Image quality is further improved by the ability to honor both vertical and tilted transverse isotropy vti and tti. During the imaging processing, it needs a large of ray travel time data. Smit, eage 63rd conference and technical exhibition, amsterdam, the netherlands, 1115 june 2001.
Ps 2d seismic lines reprocessing using prestack time migration. Integrated prestack depth migration of vsp and surface. Ions kirchhoff prestack depth migration algorithm is amplitude preserving, making it the premier choice for providing gathers for avo studies. In this paper, 3d parallel shotgather prestack depth migration with hybrid is developed and implemented. Anisotropic prestack depth migration cseg recorder. Comparison of prestack time and depthmigration data. Many competing algorithms have been proposed by various authors. Gpu implementation subsalt illumination depth imaging. Among all other methods for seismic prestack depth migration, grt is unique by. Kinematic artifacts in prestack depth migration university of. Figure e2 shows a sketch of a nonzerooffset raypath in a constantvelocity medium. The migration takes into account arbitrary shotreceiver offsets in contrast to the other migration methods within reflexw which need zero offset data as input. Raypath distortions can be so severe in areas of complex velocity variations that conventional poststack processing often.
Lawton and 2scott cheadle 1university of calgary, 2veritas dgc inc. Mickiewicza 30, 30059 krakow, poland geofizyka krakow ltd. Prestack time migration and post stack depth migration. Introduction to the traveltime tomography and prestack. A numerical implementation of kirchhoff prestack depth migration for the offset and. Traditionally, prestack depth migration psdm was considered an exotic technology, applicable only for imaging complex geology. Therefore, to get the best possible image, as predicated by the data set in figures 8. Nevertheless, kirchhoff depth migration can be efficiently run on a massively parallel computer van trier, 1991.
If the data are not evenly sampled, as in 3d surveys, implementing a kirchhoff migration algorithm would become even more complicated. Unmigrated is wrong because there are inherent velocity assumptions which makes the image incorrect. Prestack depth migration is the most glamorous step of. 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. Depth migration using kirchhoff method, akpsdm, was taken up to get a realistic depth model of the area for reservoir characterization. Data preparation for prestack migration crewes research report volume 16 2004 1 data preparation for prestack depth migration hugh d. Request pdf parsimonious 3d prestack kirchhoff depthm igration hua, b. One multilevel data acquisition strategy for parallel pre. Migrating the data, moves reflections to their correct spots. The objective of the depth migration is to improve the accuracy of the lateral positioning of the target below these. In both fields, an automatic volumetric depth residual moveout picking was used, followed by 3d gridbased tomography to derive the sediment velocity updates. Seismic prestackdepth migration grt fraunhofer itwm.
The unconformity, which is commonly occur in prestack time migration pstm section, can be removed by providing an accurate velocity model. In areas of rapid lateral and vertical velocity changes, energy is dispersed in such a way that conventional stacking with hyperbolic moveout dimin ishes both noise and signal. Because of this, depth migration is expensive compared to other data processing procedures. Promax depthcharge velocity modeling and depth imaging. A kirchhoff prestack depth migration was then run to generate offset gathers, which were then converted to angle gathers. A case study peter harris, nicholas chazalnoel, cgg americas summary the latimer county, oklahoma, area is characterised by severe thrust faulting producing dipping sediment packets. To overcome the above difficulties, i use pswave prestack depth migration of the kirchhoff type and migration. The insert highlights the zone of interest, including the unconformity and the apparent rollover and major fault. 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. Parallel 3d prestack depth migration using recursive.
Implementation of kirchhoff prestack depth migration on gpu. Delineation of karsts, a new approach using seismic. Prestack depth migration presdm is a robust method for obtaining proper image of complex. A simplified process flow for the velocity model building.
Nevertheless, the real bottleneck in 3d prestack processes is the sheer amount of input and output data. Qcompensation in complex media raybased and wavefield extrapolation approaches. Our implementation images arrivals that propagate at 90 and higher angles as turning waves. Pdf prestack depth migration of ultrashallow seismic data. Calgary, alberta, canada t2p 5e9 introduction in western canada there is only a small percentage of seismic data processed with prestack migration.
Compared to a cpu only version of the same algorithm, thenew approach delivers a significantly greater efficiency. Panorama technologies chapter 6 prestacktimeanddepth migration prestackmigrationalgorithmsarerelativelysimplevariantsofthepoststack methodologies. 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. Introduction to the traveltime tomography and prestack migration for boreholedata within reflexw in the following the use of the traveltime tomography and the prestackmigration for different types of borehole data is described.
Rtm algorithm, and ray based kirchhoff summation algorithms using the wave front reconstruction method for calculation of travel times. 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. Maud cavalca, robin fletcher and marko riedel, westerngeco. The advantage and significance of prestack migration cseg. This process is necessary to overcome the limitations of geophysical methods imposed by areas of complex geology. The final velocity model used for the final prestack depth migration. The detailed structure of the karst features at the surface and inside the shuaiba limestone was picked and inserted. Comparison of different schemes of image amplitude.
The dsr prestack migration equation, though defined for depth variable velocity, can be used to image media with strong velocity variations using a phaseshift plus interpolation pspi or split. Prestack depth migration, with a correct model, can improve the stacked image. Prestack, and poststack migration refer to different points in the processing flow at which you decided to migrate the data. Resultant anisotropic, prestack depth migration using distinctly dipping sections in the thrust sheet. 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. Parsimonious 3d prestack kirchhoff depth migration. The prestack migration allows to trace back the wavefield of single shots or constant offset data to their source. The anisotropic prestack depth migration gives better imaging and show depth of the sequences more accurately compared to, generally used, isotropic pre. Over the past two decades, there have been many prestack depth migration studies using oneway frequencydomain wave equation to compensate for attenuation and dispersion effects for the downgoing and upgoing waves dai and west, 1994. In addition to velocity model workflows, it should be noted. 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. Prestack depth migration and velocity model building geophysics. Comparison of different schemes of image amplitude correction in prestack depth migration spatially varying agc, which extends the vertical agc to include the laterally variation of acquisition and propagation effects.
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