Nmo to true zerooffset locations and reflection times, irrespective. Ddmo is computed using features extracted from figure 3a and highlighted in figure 3b. I will refer to this type of moveout for a dipping reflector as dip dependent moveout ddmo. In practice this is often a tedious manual process, and it needs to be done. Discrimination and enhancement of fracture signals on. Liner abstract waveequation dip moveout dmo addresses the dmo amplitude problem of finding an algorithm which faithfully preserves angular reflectivity while process ing data to zero offset. A method and apparatus for carrying out dip moveout correction on seismic data to provide trueamplitude seismic images use a calibration process to design a set of filters that correct the seismic amplitudes during dip moveout correction so as to provide trueamplitude imaging. Request pdf a simple efficient method of dipmoveout correction much of the success of modern seismic data processing derives from the use of the stacking. Logstretchfkpsdmo has been recently introduced in the literature. As a result, dmo correction yields an improved stacked section that is a closer representation of a zerooffset section compared to conventional cmp stack based on normal moveout. The analytic treatment developed here shows that for transverse isotropywith a vertical.
Common offset section after nmo and dm0 correction. However, numerical studies of nmo veloci ties have revealed no apparentcorrelationbetweenthe conventional measures of anisotropy and errors in the cosineofdipdmo correction dmo errors. Moon dip moveout by fourier transform with a spike 7. Waveequation dip moveout dmo addresses the dmo amplitude problem of finding an algorithm which. Seismic data are commonly modeled by a highfrequency single scattering approximation. If the reflector has a certain slope, dmo correction dip moveout correction is performed 1,5.
If the reflector has appreciable dip, then the actual movement will be slightly different. Prior application of dipmoveout correction dmo did not. The dmo operator, to be applied to commonoffset data corrected for normal moveout nmo, is based on the analytic expression for dipdependent nmo velocity. Difference is a simple method to eliminate azimuth anisotropy, we assume there are n azimuths existed applied nmo in accp gather, n is odd, and also assume the sum of all azimuth moveout is zero or close to zero, this hypothesis is very suitable for azimuth moveout correction and easy to come true, so the. We illustrate the method using land seismic data from the tacutu basin, located in the north. The normal moveout, t nmo x, is the time difference on the seismic section between the twoway traveltime, tx, at an offset x 0 and the twoway. Until now we have only discussed data processing methods that improve the signal of each separate. Method for bin, moveout correction and stack of offset vertical seismic profile data in media with dip. Click to view images of illustrations in pdf format. Nmo velocities estimated from dip moveout corrected seismograms are independent of the dips of subsurface reflectors. Attaining accuracy with depthvariable velocity dip.
Dip moveout correction dmo is needed to correct for the dip effect on stacking velocities and thus preserve events with conflicting dips during cmp stacking. A framework for dip and azimuth moveout based on a presentation at the pimsmitacs workshop on inverse problems and imaging, university of british columbia, june 910, 2001. Dip moveout dmo correction is often applied to commonoffset sections of seismic data using a homogeneous isotropic medium assumption, which results in a fast execution. The process of normal moveout nmo helps prepare the traces before they are added together. Converted wave dip moveout daniel rosales1 abstract dip moveout dmo introduces a dip dependent correction for a more appropiate transformation of prestack data into zerooffset data. Residual dip moveout in vti media residual dip moveout in vti media alkhalifah, tariq. Thus offset was handled by velocity analysis, normal moveout and stack. Born theory of waveequation dip moveout christopher l. The shot interval was based on time 6 seconds and, due to the speed of the vessel, varied between 10 and m. Here, we showed that the moveoutbased anisotropic spreading correction masc, previously developed for pwave reflections, can be. Nowadays, a standard industrial seismic processing almost always involves the constantvelocity dip moveout correction.
In practice, the quality of seismic imaging increases with the amount of data acquired. This then is followed by inverse moveout correction figure 1. In practice, the quality of seismic imaging increases with the amount of. As a result, dmo correction yields an improved stacked section that is a closer representation of a zerooffset section compared to conventional cmp stack based on normalmoveout. The nmo correction adjusts observed travel time red path to midpoint zerooffset travel time blue path. Using the fourier transformbased dmo techniques hale 1984, notfors and godfrey 1987, liner and bleinstein 1988, va is done iteratively where a. It may be emphasized that, for a horizontal reflector, nmo correction trans. Moveoutbased geometricalspreading correction for ps. The precompiled pdf file can be viewed and printed e. Converted wave dmo has been discussed in the literature by severeal authors. Unfortunately, as is well known, conventional normal moveout correction nmo introduces mispositioning of data, and hence mis. Altitude correction for semidiameter altitude correction for parallax a thorough treatment of this topic can be found in the book astro navigation demystified.
These filters can be designed and applied in any known implementation of dip moveout, in three or two dimensions. The normal moveout, t nmo x, is the time difference on the seismic section between the twoway traveltime, tx, at. Method for bin, moveout correction and stack of offset. Inverse gs introduces the correct zerooffset spreading factor into the output. Converted wave dip moveout daniel rosales1 abstract dip moveout dmo introduces a dipdependent correction for a more appropiate transformation of prestack data into zerooffset data. At the central time sample position, we sum over the dominant eigenimages of a few traces, corresponding to svd dip filtering. Alternatively, one could use the nonhyperbolic move. A method for carrying out trueamplitude dip moveout on seismic data characterised by providing a set of correction filters for application to data from seismic surveys and applying the correction filters during dip moveout correction operations on data from seismic surveys, wherein providing the set of correction filters comprises the steps of.
Dipmoveout by fourier transform geophysics geoscienceworld. It is distinguished from dip moveout dmo, the systematic change in arrival time due to a dipping layer. To correct for this we need to migrate the data prestack. Dipmoveout correction and prestack migration seismic. Speed and precision of dip moveout patrick blondel1 abstract the oil industrys need for highquality images of the earths interior has become more and more pressing in last ten years. A theoretical comparison of equivalentoffset migration. Comparison of pwave and swave data processed by dip moveout.
The dmo correction is a method for estimating the effect of dip on moveout and removing it from the records as well. Since dmo correction in anisotropic media requires knowledge of the velocity. Nmo correction pdf normal moveout correction and stacking. But in certain circumstances, many reflectors that have a high slope. Data in a local window are corrected for linear moveout corresponding to the dips before svd.
Dmo velocity analysis with jacubowiczs dipdecomposition. Abstract equivalentoffset migration is a methodology for prestackkirchhoff time migration that partially reverses the order of velocity analysis, normal moveout correction, stack, and migration. Dipmoveout dmo correction is often applied to commonoffset sections of seismic data using a homogeneous isotropic medium assumption, which results in a fast execution. Dip moveout correction dmo is a technique that converts nonzerooffset seismic data after nmo to true zerooffset locations and reflection times, irrespective of dip. A theoretical comparison of equivalentoffset migration and dip moveoutprestack imaging j. It is the objective of moveout correction to shift energy on the cmp timetrace from time t to the zerooffset time tdm.
Attaining accuracy with depthvariable velocity dip moveout. Moveout, velocity, and stacking jon claerbout in this chapter we handle data as though the earth had no dipping re. While we could use pre stack time migration, in this tutorial we will employ the dip moveout correction. Dip moveout dmo is a process that converts nonzerooffset data to true zero offset after nmo has been applied. Spherical divergence and exponential gain correction geometry assignment deconvolution single design gate, 320ms operator, 8ms gap exponential gain dmo velocity analysis every kilometer normal moveout correction and mute multiple suppression single gate. Unfortunately, as is well known, conventional normal moveout correction nmo introduces mispositioning of data, and hence misstacking, when dip is present. Nmodip filter depends on the nmo velocity of the subsurface, but removes both flat and slightly dipping reflectors without affecting the fracture signals. This arrival time is depicted on the time section in figure 5. These filters can be designed and applied in any known implementation of dipmoveout, in three or two dimensions. Test run the dip moveout operator displays a semiel liptical response to a common offset section seeded fig. Dipmoveout processing by fourier transform in anisotropic media john e.
We show that hales isotropic dmo algorithm remains valid for elliptical anisotropy but may. The required values for the correction of dip, refraction and parallax can be found in the precompiled correction pages 125 kbyte pdf file, or they can be obtained from the interactive tables below. It should be noted, however, that the method set forth below is described in much greater detail later in this application. The nmocorrection depends on the offset and the velocity. Velocity analysis using nonhyperbolic moveout in transversely. The vsp data dx s,z g,t is typically sampled in intervals t, where t is 1, 2, or 4 milliseconds. Preparation of the data for stacking estimating the nmo velocity function. Oct 31, 1989 a method for carrying out dip moveout correction on seismic data which provides trueamplitude seismic images is provided.
Dipmoveout correction is applied to data following the normal moveout correction using flatevent velocities figure 1. Nmo corrections are made under the assumption of horizontal planar reflectors. In contrast to the static correction, the correction along the trace can differ. Dipmoveout correction and prestack migration seismic data. Jan 01, 2005 residual dip moveout in vti media residual dip moveout in vti media alkhalifah, tariq. However, this process can only be done if the reflector plane is horizontal. Dip moveout processing by fourier transform in anisotropic media. Dmo velocity analysis with jacubowiczs dipdecomposition method. Dipmoveout dmo correction is applied to normalmoveout corrected prestack data to preserve conflicting dips with different stacking velocities during stacking.
Dip moveout correction dmo is a technique that converts non. If the address matches an existing account you will receive an email with instructions to reset your password. Dipmoveout by fourier transform is a method for performing dipmoveout dmo correction in the frequencywavenumber domain. Geometrical spreading of shear and modeconverted waves typically is more strongly distorted by anisotropy than that of pwaves. Prestack crewes research report volume 2001 555 cos rms stk v v.
Dmo velocity analysis with jacubowiczs dipdecomposition method david kessler and waikin chan introduction dipmoveout dmo velocity analysis va may be performed in several ways. A calibration process is used to design a set of filters that correct the seismic amplitudes during dip moveout correction so as to provide trueamplitude imaging. The nmo correction adjusts observed travel time red path to midpoint zerooffset travel. The normal moveout depends on complex combination of factors including the velocity above the reflector, offset, dip of the reflector and the source receiver azimuth in relation to the dip of the reflector. Nmo velocities estimated from dipmoveoutcorrected seismograms are independent of the dips of subsurface reflectors. Remove the moveout of azimuth anisotropy based on difference. Speed and precision of dip moveout stanford university. Diode filtering and dipfiltering in the commonoffset domain yield good results and work very well in the presence of flat reflectors. Dipmoveout processing by fourier transform in anisotropic. Dip moveout by fourier transform is a method for performing dip moveout dmo correction in the frequencywavenumber domain.
Next, the method of vsp moveout correction for media with dip is described. Dip moveout dmo correction is applied to normal moveout corrected prestack data to preserve conflicting dips with different stacking velocities during stacking. Dipmoveout processing by fourier transform in anisotropic media. Normal moveout from dipping reflectors in anisotropic media.
A simple efficient method of dipmoveout correction request pdf. Dipmoveout correction is applied to data following the normalmoveout correction using flatevent velocities figure 1. Altitude correction for dip astro navigation demystified. The nmocorrection is also called a dynamic correction. If we apply the dipcorrected nm0 transformation to equa tion 2 using ucos a as. Based on tests with synthetic data, we developed an iterative processing scheme where a sequence consisting of crossdip correction, velocity analysis and dipmoveout dmo correction is repeated until the stacked image converges. Dip moveout correction dmo is a technique that converts nonzerooffset seismic data after. A method for carrying out dip moveout correction on seismic data which provides trueamplitude seismic images is provided.
Dip moveout correction has been an integral part of a conventional processing sequence for 2d and 3d seismic data since 1985. Direct comparison of compressional p and shear s wave data in a fractured reservoir can show whether amplitude anomalies on the pwave section are associated with the presence of gas or change of lithology. Nmo correction pdf nmo correction pdf nmo correction pdf download. A simple efficient method of dipmoveout correction. Normal moveout correction and stacking nmo correction the goals of nmo correction are. A theoretical comparison of equivalentoffset migration and. Contents v issues of making a zerophase wavelet 184 issues with the normalincidence assumption and avoiding nmo stacking 190.
37 31 498 768 2 666 1122 280 1441 1320 1354 1497 234 178 1271 912 393 1561 590 1482 1123 1042 188 852 729 1602 1637 853 1594 501 339 249 1122 545 1093 1264 740 979 927