Frequency-Dependent S-Wave Splitting Parameters Analysis: A Case Study From Azimuthal Ps Data, Sanhu Area Of The Qaidam Basin, China

The Sanhu area, which is located in the eastern Qaidam Basin in China and formed of low-amplitude anticlinal and lithologic traps, is a favorable area for biogas exploration. The fracture systems in this area are characterized in detail with the use of frequency-dependent S-wave splitting parameters, which are sensitive to the size of the fractures. The results indicate that the delay time between slow and fast S-waves decreases rapidly with increasing frequency between 5 and 30 Hz, and then it slowly decreases to a stationary value at high frequencies. Moreover, the frequency-dependent delay times suggest that fractures of different scale have different 2D density distribution. The frequency-dependent orientation of the fractures suggests that large-scale fractures, which correspond to a low-frequency band (5-11 Hz), are oriented at approximately N48 degrees E and have small random disturbances. The mesoscale fractures that correspond to the dominant frequency band (12-36 Hz) are oriented along approximately N54 degrees E in the northeastern region and N45 degrees E over the remaining area. As expected, the average fracture orientation and delay time of the dominant frequency band are consistent with previous results from conventional S-wave splitting analysis in the time domain, but the frequency-dependent fracture orientation and delay time indicate finer heterogeneity and spatial anomalies. In summary, the results show the potential for accurately characterizing fracture systems using frequency-dependent S-wave splitting parameters.