Direct inversion of P-wave to S-wave velocity ratio by Lp quasi-norm sparse constraints
ZHANG Tianyue1,2, LIN Kai1,2, WEN Xiaotao1,2, ZHAO Lian1,2, ZHANG Yuqiang1,2, LEI Yang3
1. State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu University of Technology, Chengdu, Sichuan 610059, China; 2. College of Geophysics, Chengdu University of Technology, Chengdu, Sichuan 610059, China; 3. South Branch of SINOPEC Petroleum Engineering Geophysical Co., Ltd, Chengdu, Sichuan 610041, China
Abstract：The P-wave to S-wave velocity ratio（vP/vS） is a vital tool for gas reservoir identification，reservoir characterization，and lithology recognition. At present，the P-wave velocity and S-wave velocity are mainly obtained through the inversion of the reflection coefficient approximate equation，and then the vP/vS is calculated. However， this indirect calculation method creates a cumulative error. To obtain the vP/vS directly from pre-stack seismic data，this paper proposes a new generalized elastic impedance equation and further derives an approximate equation of the P-wave reflection coefficient，which is linked to the vP/vS，P-wave velocity，and density. To achieve high-precision inversion results，this paper proposes a prestack seismic inversion method based on the sparse constraint of the Lp quasi-norm utilizing the derived approximation equation of reflection coefficient，which is solved by the alternating direction multiplier algorithm. The proposed direct inversion method is applied to theoretical models and practical data and compared with the indirect inversion method. The results demonstrate that the direct inversion method exhibits higher inversion accuracy and clearer boundary characterization of gas-bearing reservoirs.
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