Prestack depth migration, velocity model building, seismic tomo. For example, the woodford formation in the anadarko basin in oklahoma has an average thickness of 300 ft at an estimated depth of 11,000 ft and exhibits a large drop in velocity, from approximately 18,000. Anisotropic depth migration and highresolution tomography. After the migration, reflector dips in the crossline and inline directions are estimated from thedepth migrated. Artificial intelligence, reservoir characterization, information, velocity model, prestack depth migration, psdm, velocity field, velocity. All data was located in a mature area of the central gulf of mexico with many complex surface. Results from the prestack depth migrations was quite significant with improved imaging. Workflow used for velocity model building with structurally constrained tomography.
Imaging complex structures inside the earth requires reasonable velocities that can be provided by applying prestack depth migration to multichannel s. The velocity model was used to perform a kirchhoff prestack depth migration of the synthetic shot gathers. Broadband velocity model building and imaging using. Initial depth model building using robust timemigration velocity. Depth processing enhances the image of the subsurface in areas where both the vertical and lateral velocity models are changing. The advent of velocity sensitive depth imaging techniques such as prestack depth migration has created a demand for more accuracy in velocity model building. A modeling and migration study of fault shadows in seismic. The dashed box shows processes iterated to obtain the best model.
The method was tested on two different datasets acquired in the polish carpathians. Building the velocity model in a highly structural setting is a very different beast fig. Case history imaging complex structure in shallow seismic. Complex model building using objective construction of. We observed a confined section of the footwall was poorly illuminated. Application of a tomographic velocity model to the. In this example, the model is colourcoded to represent the low velocity v0. Anisotropic pre stack depth migration in the absence of well control. Velocity inversions over small depth intervals cannot be corrected for and lead to incorrect layer thickness of the lower velocity interval. Pdf prestack depth migration velocity model building in complex. Use of prestack depth migration for improving the accuracy of.
Pdf improvements in seismic imaging and migrationvelocity. Prestack depth migration is an effective method for determining velocities because of the sensitivity of the migrated image to the velocity model liu, 1997. Velocity inversions over small depth intervals cannot be corrected for and lead. Details of the model at the target level are shown in figure 3a. Estimating subsurface parameter fields for seismic migration. Prestack depth migration psdm is one of the most reliable seismic techniques for imaging subsurface structures because. Feb 16, 2015 depth imaging, on the other hand, needs many passes of migration velocity model building and migration before proceeding through post migration processing. Anisotropic prestack depth migration of complex geological. 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.
From this image, correlation of different events with depth values can be made. Prestack depth migration and velocity model building for. Application of a tomographic velocity model to the prestack. Strong refraction of waves in the migration velocity model introduces kinematic artifacts.
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. 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 advent of velocity sensitive depth imaging techniques such as pre stack depth migration has created a demand for more accuracy in velocity model building. An integrated prestack depth migration workflow using model. Anisotropic model building with structurally constrained. Use of prestack depth migration for improving the accuracy. In the last decade or two, large strides have been made in seismic processing, especially in prestack depth migration. The course guides the student through paradigms recommended basic time to depth velocity analysis workflows using geodepth and time to depth migrations. Psdm velocity models for a complex geological setting. Cram is a resource intensive process, hence kirchhoffs algorithm has been used for velocity model building and refinement and cram has been used for imaging. Complex structural velocity model building for depth imaging. Tomographic velocity analysis and waveequation depth. The rms velocity volume used for earlier pre stack time migration was used for deriving initial interval velocity model in depth. A series of tomography tests was used to determine the spatial resolution limits of the velocity model.
It is a very tedious effort that requires iterative updates and remigrations. Velocity model building and seismic imaging in a complex. Calibrating prestack depth migration volumes with well. Model building prestack depth migration velocity estimation. Pdf kinematic artifacts in prestack depth migration. Figure 5 is the result of a prestack depth migration using a vertically updated velocity model. Shallow velocity model building considerations for prestack. The autoimager prestack time migration result is shown in.
Fmd will outperform kirchhoff migration in image quality in case of complex geology, and may also be used as an alternative in the iterative velocity model building due to. Prestack depth migration and velocity model building. A typical anisotropic migration velocity model made up of a set of polygons. It is thus of great interest to convert the time migration velocity to the depth domain in order to unravel inherent distortions in timedomain images and to provide a reasonable starting model for building depth imaging velocities 3. Complex structural velocity model building for depth. Pdf on sep 9, 2016, maya grigorova published comparison. It is thus of great interest to convert the time migration velocity to the depth domain in order to unravel inherent distortions in timedomain images and to provide a reasonable starting model for building depth. In areas of rapid velocity changes, energy is dispersed in such a way that. Velocity model based on tomography solution has proven itself to create detailed. Jul 22, 2019 at the same time as these advances are unfolding, prestack depth migration is beginning to see widespread use in many north american unconventional shale plays rauchdavies et al. Hereinafter the velocity model will be used for the psdm pre stack depth migration process. Weihong fei, duryodhan epili, jing xie, and young kim, tgsnopec geophysical company. Examples of application of the velocity analysis for depth prestack migration are shown.
Anisotropic depth migration and highresolution tomography in. In contrast, the velocity model for depth migration attempts to approximate the true layerbylayer interval velocities with ray bending and kinking at each abrupt change in the velocity depth model gray et al. An integrated pre stack depth migration workflow using model based velocity estimation and refinement andy furniss abstract. Further modification of the velocitymodelbuilding tools allow the creation of anisotropic velocity models for depth migration. We applied it to the 3 d segeage salt velocity model. To minimize the required iteration of depth migration, we first perform a demigration. During the past decade, a radical change has taken place in the way seismic processing delivers a subsurface image. Although we used the true velocity depth model, time migration produced the incorrect image of the basesalt boundary and the subsalt region. Integrated prestack depth migration of vsp and surface. The true utility of the shallow velocity model can only be gauged by using it in a prestack depth migration.
Figure 1 shows a structural time map for a reflection from a late cretaceous formation and the locations of the four wells in the area. This course will teach you how to use velocity information and structural inputs to build a consistent velocity model andor calibrate ones that have been created during seismic data processing. Each will be discussed in detail in the following sub. Anisotropic prestack depth migration algorithms were employed to better tie the seismic events to the well markers. Moreover, in the velocity model building of complex media, 3d prestack kirchhoff depth migration is still the working horse, due to its computational attractiveness. The strength of prestack time migration is that the imaging is kept in the time domain where insensitivity to errors in the migration velocity field result in a small loss of focusing that. Figure 8a, with the rms migration velocity field overlain. Building velocity models for steepdip prestack depth. Management david kessler, president, seismiccity, inc dr. Geodepth 3d depth velocity model building and depth imaging. Tomographic velocity model building for prestack depth migration. Hundreds of checkshots were used as a starting point for building the initial velocity model. Kinematic time migration and demigration of reflections in. Anisotropic velocity analysis, prestack depth migration and velocity model building, ian f.
Nov 15, 2008 in prestack depth migration and velocity model building brings together works published since the early 1980s, striking a balance between algorithm development and estimation of subsurface velocity and anisotropy parameters. This evolution initially began in structurally complex areas and the problems with incorrect geologic models and associated velocity fields in precise subsurface imaging. For an overview regarding velocity model building in time or depth, see robein 2003 and jones 2010. This can help build a better initial model for depth migration. In that time span, a radical change has occurred in the way seismic processing has delivered a subsurface image. Pdf carpathians geology is very complex and seismic horizons are highly deformed by tectonic movements, existence of thrusts, numerous faults and. In prestack depth migration and velocity model building seg geophysics reprint series no. Pre stack time migration pstm, pre stack depth migration. Figure 8b, but now with the interval velocity overlain calculated with the structural constraint applied. Large lateral impedance contrasts across the faults are believed to be one of the main causes for the poor seismic imaging at the rotliegend objective. Once satisfied with the refraction tomography output results, the model is further updated in a global fashion iteratively with prestack depth migration and reflection tomography algorithm for optimum results. Estimating subsurface parameter fields for seismic. Pdf divingwave refraction tomography and reflection. Kessler serves as the president of seismiccity since its incorporation in early 2000.
Shallow velocity model building considerations for. Fast velocity model building using kinematic demigration. 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 senior research. An interpreters guide to successful prestack depth. Recent approaches to estimate the time migration velocity model can be found in, for example, fomel 2003, 2007, cooke et al. Changes in the migration velocity model as it is re. Complex model building using objective construction of curve. 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. An interpreters guide to successful prestack depth imaging. 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.
Specifics of complex velocity model building for psdm hall et al. It is now commonly accepted that prestack depth migration is the best method available for accurate imaging. In time migration, the imaging velocity model often begins with the rootmeansquare rms velocity com. Figure 6 shows the migrated image after updating the model using tomography. Estimated velocity model and the corresponding image rays. An integrated prestack depth migration workflow using model based velocity estimation and refinement andy furniss abstract. In a strict theoretical sense, in the presence of lateral velocity variations, you need to image the subsurface by migration of seismic data in depth, before stack and in three dimensions. Prestack kirchhoff depth migration psdm is a robust method for obtaining proper image of complex subsurface. We present a case study of an anisotropic prestack depth migration apsdm project which used highresolution, shallow tomography and anisotropic model building for a large depth migration project in the gulf of mexico. Generic model building loop for raybased tomography. An integrated prestack depth migration workflow using. Model velocities were assigned from sonic logs from the vsp well. Because individual bins are migrated independently, the migration has no access to the bin component of slowness.
An accurate time velocity model can be of great use in the construction of an initial depth velocity model, from which a highquality depth image can be produced. We must remind ourselves that an accurate image from depth migration is attainable only when the velocity depth model is correctly defined, independent of the input data type zerooffset, stack, or prestack. Second, the automated picking takes advantage of the. An ultimate validation should come from prestack depth migration velocity analysis, which is significantly more expensive. Depth migration is a key issue for obtaining high resolution data, used for more confident and reliable structural interpretation. In the depth migrated images, they occurred as anticlines and synclines which may be false or real. The velocity model building required the integration and. The results have to be calibrated against well tops and horizons. Mickiewicza 30, 30059 krakow, poland geofizyka krakow ltd. For better migration precise velocity model is needed. Prestack depth migration presdm versus traditional poststack time migration has become a common method for seismic velocity model building and imaging. Anisotropic prestack depth migration in the absence of well control.
We conducted a numerical model test to verify prestack depth migration by the 3d pspi. Methods of velocity estimation include tomography, gatherflattening techniques, and scans on velocity perturbed stacks. When the velocity model is correct, data migrated in different. The result of the psdm overlaid with the velocity field is shown in figure 3. Prestack depth migration an ultimate aspiration for.
Imaging below dipping anisotropic strata thrust belt. In rojano et al 2005 we described an iterative approach to velocitymodel building oriented towards the integration of seismic and well data in mature fields. Fast velocity model building using kinematic demigration and migration. The first iteration of prestack depth migration uses this initial velocity model to obtain depth migrated gathers or stacks for further iterative velocity analysis and model building. The subsurface structure was sufficiently reconstructed that the velocity model could be refined through migration velocity analysis.
The processing operations applied to the data prior to prestack migration velocity model building included preprocessing, radon demultiple, and an initial velocity analysis on a 500 x 500 m grid. The velocity model time anomalies are the results of the truncation of. Prestack depth migration and velocity model building geophysics. To confirm the veracity of the interval velocity model, prestack depth migration was used. Velocity model building and pre stack depth imaging using. Fast velocity model building using kinematic demigration and. Prestack depth migrated sections with varying migration velocity. Threedimensional prestack depth migration psdm seismic processing using hardlayer model updating was applied to the data in 2000. This training manual covers basic workflows in geodepth 3d and offers students two alternatives for building the initial model, a structure independent grid based and a layer based model. Field data example of interval velocity estimation. However, all of the different model building methods rely on an existing reflection image with a. Here, we illustrate the performance of the algorithm outlined in the preceding section. Jan 01, 2005 one of nams rotliegend prospects is situated at c.
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