Gas identification using multi-wave velocity ratio parameters
Cheng Bingjie1,2, Xu Tianji3,4, Liang Qun1,2, Li Li5
1. State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, CDUT, Chengdu Sichuan 610059, China;
2. Key Laboratory of Earth Exploration & Information Technology of the Ministry of Education, CDUT, Chengdu Sichuan 610059, China;
3. Exploration & Production Research Institute, Southwest Branch Co., SINOPEC, Chengdu Sichuan 610041, China;
4. Key Laboratory of Multi Components Seismic Technology, SINOPEC, Chengdu Sichuan 610041, China;
5. GRI, BGP Inc., CNPC, Zhuozhou Hebei 072750, China
Abstract:By using joint inversion of shear wave (S wave) and compressional wave (P wave) and iterated computation to process 3D3C seismic data, we can obtain multi-waves velocity ratio parameters, including S/P wave velocity ratio, S/C wave velocity ratio, C/P wave velocity ratio, and other parameters such as velocity ratio derivative which are derived from multi-wave velocity ratio parameters. Based on the mathematical analysis between Poisson's ratio and wave velocity ratio, we get S/C wave velocity ratio, C/P wave velocity ratio, the first order derivative of C/P wave velocity ratio to P wave, and the first order derivative of C/P wave velocity ratio to Poisson's ratio by using the propagation characters of P and C wave. All of these new parameters are sensitive to lithologic and gas characters which are very useful for gas prediction. Using these new parameters in gas detection of low permeated-tight fractured reservoir in the deep Xujiahe Formation in Western Sichuan Basin, we found that well-developed fractures with high multi-wave ratios are good gas reservoirs, which means multi-wave velocity ratio parameters can be new indicators in gas reservoir identification.