Dip moveout correction dmo is a technique that converts nonzerooffset seismic data after nmo to true zerooffset locations and reflection times, irrespective of dip. Dip moveout correction dmo is a technique that converts nonzerooffset seismic data after. 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. 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. Click to view images of illustrations in pdf format. Dip moveout by fourier transform is a method for performing dip moveout dmo correction in the frequencywavenumber domain. Dmo velocity analysis with jacubowiczs dipdecomposition method. Dipmoveout correction and prestack migration seismic. Nowadays, a standard industrial seismic processing almost always involves the constantvelocity dip moveout correction. Prior application of dipmoveout correction dmo did not. 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. The nmocorrection is also called a dynamic correction. Nmo correction pdf nmo correction pdf nmo correction pdf download.
But in certain circumstances, many reflectors that have a high slope. Dipmoveout processing by fourier transform in anisotropic. If the reflector has a certain slope, dmo correction dip moveout correction is performed 1,5. Converted wave dmo has been discussed in the literature by severeal authors. The shot interval was based on time 6 seconds and, due to the speed of the vessel, varied between 10 and m. Test run the dip moveout operator displays a semiel liptical response to a common offset section seeded fig. However, this process can only be done if the reflector plane is horizontal. Dipmoveout correction is applied to data following the normal moveout correction using flatevent velocities figure 1. Attaining accuracy with depthvariable velocity dip.
Dmo velocity analysis with jacubowiczs dipdecomposition method david kessler and waikin chan introduction dipmoveout dmo velocity analysis va may be performed in several ways. Velocity analysis using nonhyperbolic moveout in transversely isotropic media. Altitude correction for dip astro navigation demystified. Thus offset was handled by velocity analysis, normal moveout and stack. The precompiled pdf file can be viewed and printed e. Nmo velocities estimated from dip moveout corrected seismograms are independent of the dips of subsurface reflectors. A simple efficient method of dipmoveout correction. Unfortunately, as is well known, conventional normal moveout correction nmo introduces mispositioning of data, and hence mis. 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. Altitude correction for semidiameter altitude correction for parallax a thorough treatment of this topic can be found in the book astro navigation demystified. 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. Nmodip filter depends on the nmo velocity of the subsurface, but removes both flat and slightly dipping reflectors without affecting the fracture signals. These filters can be designed and applied in any known implementation of dipmoveout, in three or two dimensions. 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. Method for bin, moveout correction and stack of offset vertical seismic profile data in media with dip. The dmo operator, to be applied to commonoffset data corrected for normal moveout nmo, is based on the analytic expression for dipdependent nmo velocity. If the reflector has appreciable dip, then the actual movement will be slightly different. 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. Attaining accuracy with depthvariable velocity dip moveout. Normal moveout from dipping reflectors in anisotropic media. The nmo correction adjusts observed travel time red path to midpoint zerooffset travel.
Waveequation dip moveout dmo addresses the dmo amplitude problem of finding an algorithm which. Remove the moveout of azimuth anisotropy based on difference. A simple efficient method of dipmoveout correction request pdf. Alternatively, one could use the nonhyperbolic move. Contents v issues of making a zerophase wavelet 184 issues with the normalincidence assumption and avoiding nmo stacking 190. Here, we showed that the moveoutbased anisotropic spreading correction masc, previously developed for pwave reflections, can be. 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. Moon dip moveout by fourier transform with a spike 7. The dmo correction is a method for estimating the effect of dip on moveout and removing it from the records as well. We illustrate the method using land seismic data from the tacutu basin, located in the north. Common offset section after nmo and dm0 correction. Geometrical spreading of shear and modeconverted waves typically is more strongly distorted by anisotropy than that of pwaves. Dipmoveout processing by fourier transform in anisotropic media.
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. Oct 31, 1989 a method for carrying out dip moveout correction on seismic data which provides trueamplitude seismic images is provided. The nmocorrection depends on the offset and the velocity. Logstretchfkpsdmo has been recently introduced in the literature. A theoretical comparison of equivalentoffset migration and. Until now we have only discussed data processing methods that improve the signal of each separate. Residual dip moveout in vti media residual dip moveout in vti media alkhalifah, tariq. 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. Dip moveout correction dmo is a technique that converts non. Seismic data are commonly modeled by a highfrequency single scattering approximation.
I will refer to this type of moveout for a dipping reflector as dip dependent moveout ddmo. The vsp data dx s,z g,t is typically sampled in intervals t, where t is 1, 2, or 4 milliseconds. It should be noted, however, that the method set forth below is described in much greater detail later in this application. Preparation of the data for stacking estimating the nmo velocity function. Diode filtering and dipfiltering in the commonoffset domain yield good results and work very well in the presence of flat reflectors. It may be emphasized that, for a horizontal reflector, nmo correction trans. A theoretical comparison of equivalentoffset migration. These filters can be designed and applied in any known implementation of dip moveout, in three or two dimensions. Normal moveout correction and stacking nmo correction the goals of nmo correction are. 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. Next, the method of vsp moveout correction for media with dip is described. 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. We show that hales isotropic dmo algorithm remains valid for elliptical anisotropy but may.
Nmo to true zerooffset locations and reflection times, irrespective. Moveoutbased geometricalspreading correction for ps. Dipmoveout dmo correction is often applied to commonoffset sections of seismic data using a homogeneous isotropic medium assumption, which results in a fast execution. Speed and precision of dip moveout stanford university. This arrival time is depicted on the time section in figure 5. Comparison of pwave and swave data processed by dip moveout.
Dip moveout correction has been an integral part of a conventional processing sequence for 2d and 3d seismic data since 1985. Using the fourier transformbased dmo techniques hale 1984, notfors and godfrey 1987, liner and bleinstein 1988, va is done iteratively where a. The process of normal moveout nmo helps prepare the traces before they are added together. 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. It is the objective of moveout correction to shift energy on the cmp timetrace from time t to the zerooffset time tdm.
Dip moveout dmo correction is applied to normal moveout corrected prestack data to preserve conflicting dips with different stacking velocities during stacking. At the central time sample position, we sum over the dominant eigenimages of a few traces, corresponding to svd dip filtering. In practice this is often a tedious manual process, and it needs to be done. Dipmoveout dmo correction is applied to normalmoveout corrected prestack data to preserve conflicting dips with different stacking velocities during stacking. 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. Dip moveout processing by fourier transform in anisotropic media. Nmo correction pdf normal moveout correction and stacking.
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. Dipmoveout by fourier transform is a method for performing dipmoveout dmo correction in the frequencywavenumber domain. In practice, the quality of seismic imaging increases with the amount of data acquired. Unfortunately, as is well known, conventional normal moveout correction nmo introduces mispositioning of data, and hence misstacking, when dip is present. The tests presented in this paper, conducted on the segeage. A method for carrying out dip moveout correction on seismic data which provides trueamplitude seismic images is provided.
Nmo velocities estimated from dipmoveoutcorrected seismograms are independent of the dips of subsurface reflectors. Inverse gs introduces the correct zerooffset spreading factor into the output. 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. 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. Dipmoveout processing by fourier transform in anisotropic media john e. Born theory of waveequation dip moveout christopher l. Dipmoveout by fourier transform geophysics geoscienceworld. 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. Ddmo is computed using features extracted from figure 3a and highlighted in figure 3b. Jan 01, 2005 residual dip moveout in vti media residual dip moveout in vti media alkhalifah, tariq. However, numerical studies of nmo veloci ties have revealed no apparentcorrelationbetweenthe conventional measures of anisotropy and errors in the cosineofdipdmo correction dmo errors. Nmo corrections are made under the assumption of horizontal planar reflectors. If the address matches an existing account you will receive an email with instructions to reset your password. The normal moveout, t nmo x, is the time difference on the seismic section between the twoway traveltime, tx, at.
It is distinguished from dip moveout dmo, the systematic change in arrival time due to a dipping layer. The analytic treatment developed here shows that for transverse isotropywith a vertical. Moveout, velocity, and stacking jon claerbout in this chapter we handle data as though the earth had no dipping re. Dipmoveout correction and prestack migration seismic data. To correct for this we need to migrate the data prestack. In contrast to the static correction, the correction along the trace can differ. Abstract equivalentoffset migration is a methodology for prestackkirchhoff time migration that partially reverses the order of velocity analysis, normal moveout correction, stack, and migration. The nmo correction adjusts observed travel time red path to midpoint zerooffset travel time blue path.
Discrimination and enhancement of fracture signals on. If we apply the dipcorrected nm0 transformation to equa tion 2 using ucos a as. Data in a local window are corrected for linear moveout corresponding to the dips before svd. Method for bin, moveout correction and stack of offset.
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. Since dmo correction in anisotropic media requires knowledge of the velocity. 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. Dmo velocity analysis with jacubowiczs dipdecomposition. This then is followed by inverse moveout correction figure 1. A theoretical comparison of equivalentoffset migration and dip moveoutprestack imaging j. Velocity analysis using nonhyperbolic moveout in transversely. Dipmoveout correction is applied to data following the normalmoveout correction using flatevent velocities figure 1. 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.
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