This measure is particularly attractive for analysing class. Seismic interpretations are often highly subjective and depend on the interpreters understanding of. Semblancebased coherence, eigenstructurebased coherence, and other discontinuity attributes are among the most widely applied seismic attributes today. I derive and analyse an explicit formula for a generalized semblance attribute, which is suitable for the velocity analysis of prestack seismic gathers with distinct amplitude trends. Semblance is calculated over a 3d analysis window, with a defined dip and azimuth for each point in the data volume zero dip for a flattened volume marfurt, et al. Velocity model building from seismic reflection data by. Using a version of the seismic data on which mobil had applied their parabolic radon multiple suppression, we produced denselyspaced velocity semblance scans in the midpoint direction. Such horizonbased v rms, created without additional data, can still be used to create the. Interpretation of timelapse seismic data from a heavy oil. In this paper i work with 2d data, and thus i compute semblance on 2d patches structural dip and.
For comparison, the proposed azimuthal residual velocity analysis has been performed in parallel with a conventional 2d velocity analysis in 6 azimuthal sectors, using the same cigs. Velocity analysis using both reflections and refractions in. We developed and analyzed a method for automatic velocity picking in the semblance domain as a nonlinear optimization problem that is. In this study, we developed an efficient automatic velocity analysis algorithm by using bootstrapped differential semblance bds and monte carlo inversion. If data from all channels are perfectly coherent, or show continuity from trace to trace, the semblance. Velocity analysis using similarityweighted semblance article pdf available in geophysics 804. Highlightsas has been explored everything depends on vx, y, z, and this remains as the most important and difficult problem in seismic exploration. While the conventional semblance can be interpreted as squared correlation with a constant, the. An inverse semblance value is assigned to the center of the spatial and time window for each point in the 3d seismic volume then output to the visualization or seismic. Semblance analysis allows for the refinement of seismic data. A case study from mumbai offshore basin mithailal, cps rana, bn bhatta, d chatterjee, dr. Complex semblance and its application springerlink. Velocity analysis using ab semblance, geophysical prospecting.
This is done by developing a velocity spectra display to determine the velocity through different layers at depth. Reducing the gap between seismic imaging and geology. We present a method for automatic velocity analysis of seismic data based on differential semblance optimization dso. In this paper, we propose a new velocity analysis method by using highresolution semblance based on sparse hyperbolic radon transform shrt. Automatic seismic velocity analysis based on nonlinear. In this paper i demonstrate an alternate method to estimate the semblance. Semblance analysis is a process used in the refinement and study of seismic data. Semblance measures the lateral coherency of the seismic events in a common midpoint gather, and it has been widely used for the normalmoveoutbased velocity estimation. Successful application of horizon velocity analysis for imaging in seismically obscure area. The isolation of such patterns and the use as possible identifiers of subsurface characteristics constitutes attribute analysis and can significantly impact reducing risk in hydrocarbon prospecting. The seismic attribute is dependent, at least in part, on the ratio of the square of the sum of the amplitudes of said traces within the window and the sum of the squared amplitudes of.
A semblance attribute to more reliably detect a seismic discontinuity is provided. Cahoj, sumit verma, bryce hutchinson, jie qi and kurt j. This thesis develops a new computation of the objective function and gradient for normal moveoutbased differential semblance ds. Automatic velocity analysis of crosswell seismic data guoping li and robert r. The semblance velocity analysis method is widely used for stacking velocity analysis of seismic reflection data taner and koehler 1969. Velocity analysis using similarityweighted semblance. During analysis, the user has up to four windows to help pick velocities and eta values. The traditional algorithm has a difficulty at zerocrossings of seismic recordings. Introduction semblancebased coherency measures are commonly applied to perform velocity analysis taner and koehler, 1969. Automatic velocity analysis using bootstrapped differential.
Applying velocity continuation to migration velocity analysis involves the following steps. Azimuthal residual velocity analysis in offset vector for. While the conventional semblance can be interpreted as a squared correlation with a constant, the ab semblance is defined as a correlation with a trend. Conventional velocity analysis of seismic gathers scans different values of effective moveout velocity, computes. Based on semblance analysis, this method derives velocities from crosswell direct arrivals in an automatic manner and so avoids timeconsuming hand picking of. Seismic refraction interferometry with a semblance analysis on the crosscorrelation gather dylan mikesell 1and kasper van wijk abstract crosscorrelating wavefields recorded at two receivers to produce data as if one receiver was a source is commonly referred to as seismic interferometry, or the virtual source method. The accuracy of the velocity model depends on ones ability to pick the correct velocity, which in turn depends on the. Inversion velocity analysis via differential semblance.
Successful application of horizon velocity analysis for. Velocity analysis using highresolution semblance based on. The interactive globe claritas velocity analysis cva application is an excellent tool for velocity analysis of onshore or offshore data. The problem with a dso type approach is that it is quite expensive and sensitive to noise.
Semblance based moveout analysis is routinely used in seismic data processing to estimate stacking moveout velocity v. Simultaneoussource shooting is a breakthrough in modern seismic acquisition. Velocity analysis of simultaneoussource data using high. The ds principle underlies a class of algorithms for seismic velocity analysis. When different values for x and t are plotted, the slope can be used to. Picking of velocities from constant velocity corrected gathers and. Seismic velocity analysis methods can be divided into two groups. The semblance basically measures the coherence of events along hyperbolic traveltime curves with different velocities. Differential semblance velocity analysis in the differential semblance velocity analysis, the velocity can be updated by making use of the property the cig has that the velocity is correct when the energy in cigs concentrates around the zero offset.
While the conventional semblance can be interpreted as squared correlation with a constant, the semblance is defined as a correlation with a trend. Therefore, discontinuity attributes most often are applied to highlight faults in a seismic volume but are also useful in detecting subtle stratigraphic features in map view. The nip is where you have the shot and the geophone in the same location and the path taken by the recorded sound waves is. Introduction semblance based coherency measures are commonly applied to perform velocity analysis taner and koehler, 1969. Stewart abstract a new method for velocity analysis of crosswell seismic data is discussed in this paper. Selforganizing maps som is a powerful cluster analysis and pattern. The new data received following the semblance analysis is usually easier to interpret when trying to. Jun 10, 2011 to properly understand seismic wave propagation in unconsolidated sand layers, it is important to estimate the parameters of their continuous velocitydepth functions.
Automatic velocity analysis of crosswell seismic data. We will now sum different traces, also called stacked, to improve the signalto. This process is experimental and the keywords may be updated as the learning algorithm improves. Tools for velocity analysis velocity spectrum or semblance best modern method industry standard define time window in which wavelet is contained calculate hyperbolic trajectory measure coherency of trace signal, e. Velocity analysis and nmocorrection until now we have only discussed data processing methods that improve the signal of each separate trace. Seismic refraction interferometry with a semblance analysis. The result of this loop operation is a timedistance map of seismic velocity distribution, v s t 0, x, based on cmp families. Pdf velocity analysis using similarityweighted semblance. This study proposes a procedure to estimate the v 0 and k parameters of a specific velocity function, where v 0 is the direct pwave velocity at the ground surface and k is the velocity gradient. Semblance, coherence, and other discontinuity attributes.
An imagefocusing semblance functional for velocity analysis. When these crosscorrelations are summed over the boundary of sources, the resulting greens function estimates along a receiver array contain nonphysical or spurious refracted energy. Either tomography based velocity analysis or bornapproximation waveequation based velocity inversion, requires an initial acceptable velocity model from the very noisy blended data fig. In the next section, we will introduce a way for obtaining highresolution and highfidelity velocity spectrum from blended data, using. An alternative approach to differential semblance velocity. Symes, yin huang,and zhenchun li, china university of petroleum huadong,rice university summary migration velocity analysis mva is an approach to solve a. Velocity analysis using absemblancea apublished in geophysical prospecting, v. The use of this technique along with other methods makes it possible to greatly increase the resolution of the data despite the presence of background noise. Semblance analysis semblance analysis offers a somewhat more processed version of the same information available in the constant velocity panels. Estimation of velocity function parameters in unconsolidated. I derive and analyze an explicit formula for a generalized semblance attribute, which is suitable for velocity analysis of prestack seismic gathers with distinct amplitude trends. Semblance analysis semblance analysis offers a somewhat more processed version of the same information available in the constantvelocity panels. This problem is alleviated by applying a smoothing window at the cost of losing vertical resolutions.
Seismic refraction interferometry with a semblance. The semblance velocity tool will perform interactive velocity and fourth order eta picking using semblance. May 01, 2009 velocity analysis using ab semblance fomel, s. Semblance, a measure of similarity or coherence is discussed along with the interpretive side of the velocity analysis process. First, we define a new semblance weighted by offset i hi 4. Semblance cva is performed via manual picking of points to construct a curve of velocity versus time in the semblance domain, in a loop over the cmps to cover the entire seismic section. In this paper, we present the current results of the avo dataset analysis, including a highresolution velocity analysis, stacking and migration of the data. Ab semblance is theoretically derived from a squared correlation coefficient of seismic data with a trend function by inputting traces of cmp gather for the velocity analysis fomel 2009. The data are mapped for each offset from the time domain to the depth. Semblance is a seismic attribute, used to analyze data for changes in the seismic character, computed by comparing the amplitude of a single trace to that of an adjacent trace. Automatic seismic velocity analysis based on nonlinear optimization of the semblance function. The easiest way to accomplish this is by recording the normal incidence path nip. If data from all channels are perfectly coherent, or show continuity from trace to trace, the semblance has a value of unity. These numbers represent a measure of signal coherency and semblance along the hyperbolic trajectories governed by velocity, offset, and traveltime.
Rice university an alternative approach to differential. Virieux and operto, 2009, while the second group aims at improving the quality in the image domain, such as mi. Seismic data automatic gain control velocity analysis downward continuation record section these keywords were added by machine and not by the authors. The semblance attribute of the center point of a seismic volume is calculated from 3d traces within a spatial and time window. Semblance, a measure of multitrace coherence, has been used extensively in seismic data processing and interpretation such as velocity analysis and fault detection. Estimation of directarrival velocity using the linear. Differential semblance velocity analysis via rtm 2 s u f and s v d 2, where s is the impedance matrix, u and v are the forward modeled and backpropagated wave fields to be determined. One of the best solution to this type of problem is the differential semblance operator dso approach symes and carazzone, 1991. Pdf automatic velocity analysis by differential semblance.
The mathematical inverse of the semblance attribute can be calculated to identify seismic event discontinuity in 3d seismic surveys, e. A quantitative measure of the coherence of seismic data from multiple channels that is equal to the energy of a stacked trace divided by the energy of all the traces that make up the stack. Abstract the goal of automatic velocity analysis is to extract accurate velocity from voluminous seismic data with efficiency. The current stack or range of inlines is displayed, and the user can then perform cvs, cvg or semblance analyses in realtime, on any part of the seismic section. Globe claritas velocity analysis nz transport agency. A window contains the current cdp gather, that can also be expanded to a super gather. Automatic velocity analysis by differential semblance. Understanding attributes and their use in the application. Inversion velocity analysis via differential semblance optimization in the depthoriented extension yujin liu, william w. S viswanathan, ongc summary velocity undoubtedly is the asset upon which the entire understanding of the seismics relies upon. The result of this loop operation is a timedistance map of seismic velocity distribution, v s. Avosensitive semblance analysis for wideazimuth data.