Preliminary analysis of seismic attenuation and heterogeneities in Weiyuan Shale Gas Field: Coda Q and Peak delay time analysis

During hydraulic fracturing (HF) stimulation in unconventional reservoir development, seismic attenuation significantly affects high frequency microseismic data. Analyzing attenuation parameters, including scattering and absorption, provides valuable insights into reservoir properties and changes that result from HF injections. These attenuation parameters were mapped in 3D using the MuRAT (multi-resolution seismic attenuation tomography) software with a dataset of approximately 32,000 events over two years in the Weiyuan shale gas field (WSGF). Firstly, the coda quality factor Qc (intrinsic absorption), which quantifies coda wave energy loss, is calculated at large lapse time in three frequency bands (3, 6 and 9 Hz). Subsequently, we measure the peak delay time, the time lag between the direct S-wave onset and the highest amplitude arrival. Our preliminary results show that Qc has strong absorption at lower frequencies in specific volumes compared to higher frequencies. Meanwhile, peak delay times indicate consistently stronger scattering along the Weiyuan anticline and Molin fault structures across all frequency bands. We propose that the observed strong absorption is associated with the reservoir and injected fluid, while scattering is linked to pre-existing structural heterogeneities and unmapped faults.