Microseismic attenuation tomography of coalbed methane hydraulic fracturing zones

Abstract Hydraulic fracturing is widely applied for efficient coalbed methane (CBM) extraction, with microseismic monitoring providing critical insights into the spatial distribution of fracturing zones. However, using only microseismic event locations may bias fracturing zone characterization, as some areas can be aseismic. In this study, to better delineate fracturing zones, we use seismic attenuation anomalies by conducting microseismic attenuation tomography. This study utilizes microseismic waveform data associated with two hydraulic fracturing wells for the CBM extraction in a coal mine in Shanxi, China. First, the amplitude spectra of the P- and S-wave waveforms are used to determine t*, a path attenuation parameter that represents the cumulative attenuation along the ray paths between events and stations and is related to the quality factor Q. Then, t* values are used to invert for three-dimensional Qp and Qs models based on the existing velocity models and microseismic event locations, respectively. In this study, microseismic events in the fracturing zones are associated with relatively high Q values compared to the shallower zones. Based on previous laboratory studies, gas saturation zones are characterized by high Q anomalies. Therefore, we can use high Q areas around the hydraulic fracturing wells to delineate effective fracturing zones, which are also associated with low Vp and high Vs anomalies. Our study shows that microseismic attenuation tomography can be used to delineate the fracturing zones and to evaluate the gas saturation state for the case of coalbed methane hydraulic fracturing.