S-wave seismic data interpretation for gas reservoir at Sanhu area, Qaidam Basin, west China

The Qigequan Formation at the Sanhu area of the Qaidam Basin in western China is a significant gas producing formation. However, the conventional P-wave seismic survey conducted in this region reveals the presence of extensive gas clouds that strongly attenuate P waves, resulting in substantial uncertainty regarding the subsurface structure. To address this challenge, a 3D-9C seismic survey was conducted to produce S-wave reflection data unaffected by gas clouds and yielding remarkably clearer subsurface images with a higher level of confidence. The processing of the S-wave data largely used conventional P-wave processing techniques, except for S-wave splitting, which produced distinct fast (S1) and slow (S2) S-wave data sets. Notably, the S2 data exhibited superior quality compared with the S1 data, enabling us to apply various seismic attribute techniques to extract geologic features. To validate our findings, we cross reference the seismic attribute results with well-log and production data, revealing a pronounced spatial correlation between the gas reservoir and channel structure, as the prime targets for potential gas reservoirs.