Method and principle for seismic migration and imaging. Migration is a process by which reflection events in. Because diffraction energy is generally weak in seismic data and particularly in prestack data, noise attenuation and edge enhancement methods are applied on the instantaneous phase of the seismic. Input data include the stacked seismic data and well log information. Prestack kirchhoff migration is based on the scatterpoint principle that assumes reflectors may be defined by scatterpoints, and that prestack seismic data becomes the superposition of the. Seismic data is bandlimited, reducing resolution and quality. The continuation operator is only one part of the prestack migration. In the coming months we will begin to populate this sourceforge project with pure java code for reading and writing prestack seismic data.
Similarly, seismic attributes generated on noisecontaminated data. Calgary, alberta, canada t2p 5e9 introduction in western canada there is only a small percentage of seismic data processed with prestack migration. For all 3d and 2d data the following datasets were created and output in segy format. Our gaussian packet migration gpm with full imagegather output offers a new migration approach in terms of speed, frequency content, and underlying algorithm. Prestack depth migration an ultimate aspiration of subsurface imaging in geologically complex area 2 imaging to meet the exploration objectives which were much more difficult to decipher using time data.
The traveltime tomography allows to build a velocity model from the first arrival traveltimes. Figure e2 shows a sketch of a nonzerooffset raypath in a constantvelocity medium. Too coarse a spatial sampling, that is, too large a geophone group interval, may preclude high resolution imaging of steep reflectors by any migration. The prestack gathers are only about 6 gbytes, making it an excellent dataset for training and demonstrations.
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. 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. Prestack depth migration an ultimate aspiration for. The successful execution of every depth imaging project lies at the core of our services. Wellto seismic match, zerophasing of data in zone of interest and extraction of the wavelet. In order to obtain maximum value from your recorded seismic, you need to condition it suitably. Many excellent manuscripts have recently been written about the estimation of seismic interval velocities by optimizing prestack depth migration. The best approach to use varies depending on the goal model building, migration, avo and stacking all have different requirements for the input data. Only the seismic velocity must be known which, unfortunately, is no small feat in. This is 2d and 3d seismic reflection data from utah forge phase 2c.
The 2016 seismic data release packages together with well data and other geological information are available for download via the uk national data repository new, openlyavailable seismic and well data. Lawton abstract a general prestack depth migration algorithm has been developed to investigate combined depth imaging of vsp and surface seismic data. Another advantage of prestack kirchhoff migration is its ability to accommodate irregular topography. Prestack, and poststack migration refer to different points in the processing flow at which you decided to migrate the data. A prestack migration to obtain image gathers is preferred before the avo analysis, especially in areas of complex subsurface geology. Exercise in prestack migration under the born approximation.
Our results show that incorporation of higher order anisotropy under certain geology improves migration of wide azimuth waz acquisition data, and produces focused migration. Prestack event interpretation uses a true 4d tracker, seeded from gather picks and horizons. Factors affecting avo analysis of prestack migrated gathers. We demonstrate the capability of our algorithm for orthorhombic anisotropy using synthetic and real data examples from the gulf of mexico. Migration of seismic data university of california, davis. Seismic data are usually contaminated with two common types of noise, namely random and coherence. 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. Smallscale geologic features such as thin channels, or subtle faults, etc. In this paper, we demonstrate for the pamberi area of the columbus basin of eastern offshore trinidad, that further to the improvement over the conventional 3d towedstreamer time imaging from 4c anisotropic prestack time migration johns et al. Kirchhoff prestack time migration kpstm is an excellent tool that accurately images geological settings characterized by complex structure with relatively gentle velocity gradients. To understand the distinction between impedance and reflectivity, refer to figure 1, which shows the different ways in which geologists and geophysicists look at their data. Recently its application has expanded to include generating migrated gathers for avo analysis. To download this file you first sign in to your schlumberger. In the following, we first describe the involved coordinates of the recording and time migration domains of the seismic data, the principles of pre stack time migration, the properties of the diffractiontime function, the underlying time migration velocity model, and the reflectiontime parameters in the two data.
When the reflector geometries that give rise to this problem have a 3d behavior, it is necessary to image the subsurface using 3d prestack time migration. 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. As stated early in the chapter, the rigorous solution to the problem of conflicting dips with different stacking velocities is prestack time migration. Depth imaging proccessing and software seismiccity inc. To extend the frequency band available, lowfrequency data is derived from log data, pre stack depth or time migrated velocities andor a. Prestack depth migration of wideangle seismic data represents an extension of traditional imaging with nearvertical incidence data because it includ. He has developed software for the seismic processing industry and has specialized in the areas of static analysis, velocity estimation, and seismic migration. Seg does not own or maintain all the data listed on this page. Prestack and poststack migration of crookedline seismic reflection data. Prestack gaussianbeam depth migration geoscienceworld. The boundary conditions and imaging conditions are of the same importance. Prestack partial migration geophysics geoscienceworld. Introduction to the traveltime tomography and prestack migration for borehole data within reflexw in the following the use of the traveltime tomography and the prestack migration for different types of borehole data is described.
Available dataset used for this study include a full 3d prestack time migration prestm seismic volume and suites of wire line log comprising gamma ray, densityneutron, resistivity, shear and compressional velocity from nine wells as shown in table 2. He started his industrial career as a research geophysicist developing algorithms for velocity estimation, model building and prestack depth migration. Migration is the process of correcting these dip and positioning errors as an automatic digital procedure. Pdf seismic inversion methods and some of their constraints. This is a good line to start experimenting with open data and su because there is a full processing sequence including data download, reformat, header loading, gain, prestack fk filter, brute velocity estimation, brute stack, residual statics, final velocity analysis, final stack, and two types of post stack migration. Our services include the three components required for successful execution of a depth imaging project.
Unprocessed shot records with geometry loaded in trace headers a time window of processed prestack gathers with moveout applied a final image vsp data well logs inversion results to download, see instructions below. The most important rule in preconditioning of seismic data for avo analysis is to preserve the relative amplitude information during each individual processing step. Citeseerx document details isaac councill, lee giles, pradeep teregowda. The domain studied in the prestack wave migration is the lower half space, i. Kinematic time migration and demigration of reflections in. In pre stack migration, seismic data is adjusted before stacking sequence occurs. Statoil integrates pre and poststack seismic data prosource seismic improves data access, quality, and.
Pdf prestack and poststack migration of crookedline. Another resource for seismic processing algorithms actually a full seismic processing system is the colorado school of mines seismic unix system. Prestack kirchhoff depth migration of shallow seismic data. Application of crossplot and prestack seismicbased. Figure 5 shows the improvement in imaging of the steep flank of a salt dome achieved by poststack migration when applied to dmoprocessed data. This is not possible with prestack stolt migration which generates a volume of prestack migrated data. Migration is an inverse process, in which the recorded waves are propagated back to the corresponding reflector locations. Bancroft published in the cseg recorder november 2001 abstract the kinematics of prestack data considers an arbitrary offset between the source and receiver. Poststack processing steps for preconditioning seismic data. Prestack migration has become a standard component of seismic data imaging. However, the prestack partial migration provides the interpreter with a highquality common midpoint cmp stacked section which can be subsequently migrated. Citeseerx prestack imaging of compressed seismic data.
Obtaining highresolution images of the underground geological structures using seismic reflection data in prestack or poststack domain is crucial for exploration of oil and gas deposits. This workflow combines the advantages of pre stack time migration and pre. 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. A case study from the south portuguese zone fold belt, southwestern iberia. Us20060062083a1 method for depth migrating seismic data.
The robust alternative in practice is to apply nmo and dmo corrections followed by poststack time migration. The first few 3d seismic surveys were acquired in the late 1970s, but it took until 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. This paper presents a 2d and 3d prestack depth migration in anisotropic media for pwaves. The prestm seismic volume and three wells a, c and ag002xx were qualitychecked qc and prepared for seismic. In order for images produced from seismic data to correspond accurately to the spatial distribution of subsurface structures and compositional changes in the earths subsurface, techniques known generally as time migration and depth migration are performed on the seismic data. The advantage and significance of prestack migration cseg. The plan involved migrating all of statoils seismic data to prosource seismic software, and improving quality management with a new data tracking and reporting portal.
Prestack migration reservoir characterization schlumberger. Details of the model at the target level are shown in figure 3a. The readme file containing an explanation of the data including data formats, software that can be used, processing, and projection and datum used. Prestack migration is always superior if there is dip involved. Simultaneous anisotropic prestack depth migration of ps vsp and surface seismic data m. Geological background of the study area the envisaged area under study falls to the south west of. Case study data management highlevel seismic data flow and process. Normal moveout nmo and stacking of csp gathers is performed to complete the prestack migration.
Model velocities were assigned from sonic logs from the vsp well. Simultaneous anisotropic prestack depth migration of ps vsp. This paper presents a prestack gaussian beam migration method that operates on commonoffset gathers. In particular, the recent research of etgen 1990, stork 1992 and whitmore and garing 1993 illustrate data. Integrated prestack depth migration of vsp and surface. A library of matlab code for analysing post migration prestack seismic data. The effect of 3d prestack seismic migration on seismic coherence and amplitude variability walter e. In the process of seismic data acquisi tion the upward traveling waves are recorded at the surface. In kinematic time migration one maps the time, slope and curvature characteristics of seismic reflection events, referred to as reflectiontime parameters, from the recording domain of the seismic data to the time migration domain.
The method is efficient because the computation of beam superposition isolates summations that do not depend on the seismic data. Migration of seismic data can move dipping events to their correct positions, collapse diffractions and increase spatial resolution. Geomages kpstm is a full kirchhoff diffraction summation algorithm that includes advanced antialiasing filters and is capable of imaging extremely large. Marfurt abstract we compare the effect of 3d poststack versus 3d prestack imaging on seismic coherence, seismic amplitude, and seismic amplitude variation. The first few 3d seismic surveys were acquired in the late 1970s, but it took until the early 1990s before they gained general acceptance throughout the industry.
Common scatter point csp gathers are created as an intermediate step for each output migrated trace. Kirchhoff prestack depth and time migration the most widely used migration algorithm in the industry. Bancroft published in the cseg recorder november 2001 abstract the kinematics of prestack data. The motivation behind this study was to locate an underground building buried in a waste disposal. Post stack data, just tells you that rock changed to a different rock type, roughly here. The goal is to learn how to compute prestack migration images under the born approximation for prestack data. Using matlab beyond the geophysicists sandbox highlights charles jones and james selvage, bg group within the seismic geophysics community, matlab is generally considered a useful tool for developing prototype algorithms, but not for scaling to production. After thorough pre stack processing and accurate model building, optimally migrate your seismic to obtain the best images of the subsurface. The surface of the earth at z 0 acts as a mirror in reflection wave propagation, producing a correction term to the integral in eqn 5. Flow diagram of a method for optimizing seismic poststack migration by use of well log information. The additional accuracy of either dmo or prestack migration over that of conventional poststack migration demands special care in the field acquisition of seismic data.
Prestack migration an overview sciencedirect topics. Bg group plc or any of its respective subsidiaries, affiliates and associated companies or by any of their respective officers, employees or agents makes no representation or warranty, express or implied, in respect to the quality, accuracy or usefulness of this repository. The concept of migration can be summarized in the following terms. Compensation for absorption and dispersion in prestack. As outlined by figure 1, our optimization methodology for poststack migration involves the steps of data input, initialization, migration, and inversion. Raybased prestack depth migration for orthorhombic media. Westerngeco has an extensive range of prestack migration algorithms to handle all geological complexities and seismic acquisition environments and designs, including the latest fullazimuth surveys. Jul 19, 2016 by joanne wang prestack seismic data is applied routinely in the process of quantitative seismic interpretation qsi to generate varieties of seismic attributes, in order to estimate reservoir. For that reason it is common to create a new velocity field after pre stack time migration, and, in some cases, run a second iteration of the pre stack time migration with that new velocity model. Our range of algorithms includes kirchhoff, beam, controlled beam migration cbm and reverse time migration. Achieve a trueazimuth internal multiple model utilizing both seismic data and interpreted horizons. Open data on the seg wiki is a catalog of available open geophysical data online. 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. In prestack time migration, we discussed 2d prestack time migration as the rigorous solution to the problem of conflicting dips with different stacking velocities.
Unprocessed shot records with geometry loaded in trace headers a time window of processed prestack gathers with moveout applied a final image vsp data well logs inversion results to download. The prestack migration tool automatically controls the correct geometry. He continues to develop a fast prestack migration for conventional and converted wave data, prestack migrated statics analysis, and prestack migration of vertical array data. However, like the other prestack migration methods, kirchhoff prestack time migration also suffers from the angledependent stretching effect, which narrows the amplitude spectra of seismic data.
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. Kirchhoff prestack depth and time migration schlumberger. Kessler serves as the president of seismiccity since its incorporation in early 2000. The theory of prestack partial migration is based on the double squareroot equation, which describes seismic. Such noise, if not tackled appropriately, prevents their accurate imaging.
This page documents geophysical data that is readily available for download from the internet, via mail, or through special request. We use our proprietary prestack kirchhoff time migration algorithm, pstm3d, to image both pp and ps data for both 2d and 3d datasets. Introduction prestack depth migration algorithms are usually divided into two classes. The petrel prestack seismic interpretation plugin enables prestack seismic visualization, interpretation, and interactive processing to bridge the gap between prestack and poststack interpretation workflows. Optimization methods for prestack and poststack migration. Bg group plc or any of its respective subsidiaries, affiliates and associated companies or by any of. Threedimensional 3d seismic surveys have become a major tool in the exploration and exploitation of hydrocarbons. Assuming an acoustic vti medium, the double square root dsr equation becomes dependent only on the migration velocity field and the parameter. Quality control and preconditioning of the input data. Use broadband 2d seismic data to enhance prospectivity of frontier basins and plays offshore sri lanka. The flexibility of the kirchhoff algorithm in terms of ordering and density of input and output makes it ideal for the migration of land seismic data. Migrating the data, moves reflections to their correct spots. Prestack depth migration of dense wideangle seismic data.
Prestack kirchhoff depth migration is applied successfully to shallow seismic data from a waste disposal site near arnstadt in thuringia, germany. Anisotropic pp and psv prestack depth migration of 4c obc. 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. Management david kessler, president, seismiccity, inc dr. The effect of 3d prestack seismic migration on seismic. Introduction to the traveltime tomography and prestack.
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