Influence of attenuation on borehole microseismic focal mechanism inversion using different source models

Fracture directionality, scale and stress state of hydraulic fracturing areas are extremely important for the development of unconventional oil and gas. These informations can be obtained from the study of microseismic focal mechanisms. When a microseismic event happens, its seismic wave will propagate in the shale layer. Due to its high-frequency characteristic and shale reservoir's strong attenuation, the signal's amplitude and frequency received will change. If we ignore the attenuation effect and use velocity models without Q to do the microseismic focal mechanism inversion, the results may be deviate from the correct.

In this paper, our study focus on the attenuation's impact on the borehole microseismic focal mechanism inversion when using different source models (Double Couple, General Dislocation, and Moment Tensor). We performed several synthetic tests with different seismic attenuation variables, and according to our tests, the seismic attenuation's influence is significant and cannot be ignored. If the attenuation variable of the medium model in the inversion is not in accordance with the actual situation, the microseismic source inversion results, including faults' strike, dip and rake angles, scalar seismic moment, and the percentages of tensile or CLVD, ISO and DC, will deviate from the correct value. These analysis results can help us to evaluate the inversion results of the focal mechanism.