Prestack migration velocity analysis based on simplified two-parameter moveout equation

Abstract

Stacking velocity V C2 , vertical velocity ratio γ 0 , effective velocity ratio γ eff , and anisotropic parameter χ eff are correlated in the PS-converted-wave (PS-wave) anisotropic prestack Kirchhoff time migration (PKTM) velocity model and are thus difficult to independently determine. We extended the simplified two-parameter (stacking velocity V C2 and anisotropic parameter k eff ) moveout equation from stacking velocity analysis to PKTM velocity model updating and formed a new four-parameter (stacking velocity V C2 , vertical velocity ratio γ 0 , effective velocity ratio γ eff , and anisotropic parameter k eff ) PS-wave anisotropic PKTM velocity model updating and process fl ow based on the simplifi ed twoparameter moveout equation. In the proposed method, first, the PS-wave two-parameter stacking velocity is analyzed to obtain the anisotropic PKTM initial velocity and anisotropic parameters; then, the velocity and anisotropic parameters are corrected by analyzing the residual moveout on common imaging point gathers after prestack time migration. The vertical velocity ratio γ 0 of the prestack time migration velocity model is obtained with an appropriate method utilizing the P-and PS-wave stacked sections after level calibration. The initial effective velocity ratio γ eff is calculated using the Thomsen (1999) equation in combination with the P-wave velocity analysis; ultimately, the final velocity model of the effective velocity ratio γ eff is obtained by percentage scanning migration. This method simplifi es the PS-wave parameter estimation in high-quality imaging, reduces the uncertainty of multiparameter estimations, and obtains good imaging results in practice.