3D angle‐domain common‐image gathers for migration velocity analysis

Abstract

We analyze the kinematic properties of offset-domain Common Image Gathers (CIGs) and Angle-Domain CIGs (ADCIGs) computed by wavefield-continuation migration. Our results are valid regardless of whether the CIGs were obtained by using the correct migration velocity. They thus can be used as a theoretical basis for developing Migration Velocity Analysis (MVA) methods that exploit the velocity information contained in ADCIGs.We demonstrate that in an ADCIG cube the image point lies on the normal to the apparent reflector dip, passing through the point where the source ray intersects the receiver ray. Starting from this geometric result, we derive an analytical expression for the expected movements of the image points in ADCIGs as functions of the traveltime perturbation caused by velocity errors. By applying this analytical result and assuming stationary raypaths, we then derive two expressions for the Residual Moveout (RMO) function in ADCIGs. We verify our theoretical results and test the accuracy of the proposed RMO functions by analyzing the migration results of a synthetic data set with a wide range of reflector dips.Our kinematic analysis leads also to the development of a new method for computing ADCIGs when significant geological dips cause strong artifacts in the ADCIGs computed by conventional methods. The proposed method is based on the computation of offsetdomain CIGs along the vertical-offset axis (VOCIGs) and on the "optimal" combination of these new CIGs with conventional CIGs. We demonstrate the need for and the advantages of the proposed method on a real data set acquired in the North Sea.

Microseismic imaging using a source-independent full-waveform inversion method

“…With this modified extended imaging condition, we may check both the velocity model and the source image are correct or not. Angle domain common image gathers (ADCIG) is another tool that can show whether the migration velocity is correct (Sava and Fomel, 2003;Biondi and Tisserant, 2004). If the migration velocity is correct, the reflectors in the ADCIG will be flat and located at the right depth.…”

A Quadratic precision generalized nonlinear global optimization migration velocity inversion method

“…After multiple iterations of pre-stack depth migration and velocity model updating, we can finally obtain an optimal migration velocity model. Presently, there are two types of pre-stack depth migration velocity analysis, depth focusing analysis (DFA) (MacKay and Abma, 1992;Wang and Pann, 1998;Liu et al, 2001, Liu et al, 2005 and residual velocity analysis (RVA) (Al-Yahya, 1989;Liu andBleistein, 1995, Liu, 1997;Zhou et al, 2001;Biondi and Tisserant, 2004). Liu et al (2005) and Liu and Wang (2006) demonstrated that event leveling in RVA is equivalent to equating imaging depth and focusing depth in DFA.…”

Narrow‐azimuth migration of marine streamer data

“…This condition must be fulfilled by all the events that are correctly focused at zero offset because two lines passing through the same point are coplanar. The coplanarity condition can be easily applied on the prestack image after transformation into the Fourier domain, possibly at the same time that ADCIGs are computed using a 3-D generalization of the method described by Sava and Fomel (2003), as presented in Biondi et al (2003).…”