Impact of source models on focal mechanism inversion in hydraulic fracturing distributed acoustic sensing monitoring

Abstract

Distributed acoustic sensing (DAS) has garnered growing attention for microseismic monitoring in hydraulic fracturing (HF) operations within unconventional oil and gas development. Conventional DAS sensors acquire single-component measurements along the optical fiber, which may introduce uncertainties in microseismic focal mechanism inversion—a critical step for HF performance assessment and reservoir stimulation optimization. This study evaluates the performance of double-couple (DC), general dislocation (GD), and moment tensor (MT) source models for microseismic focal mechanism inversion using downhole DAS data. We systematically investigated the effects of DAS array orientation, input focal mechanism, noise level, velocity uncertainty, and source location error on the inversion results. Our findings indicate that DAS-based focal mechanism inversion was strongly controlled by the horizontal source-receiver azimuthal coverage. For a horizontal-vertical DAS acquisition geometry, MT inversion exhibited sensitivity to dip-slip input mechanisms, 5% velocity errors, 10 m source location errors, and 40% noise levels, whereas DC and GD inversions remained comparatively robust. Given that HF-induced microseismic events may involve non-DC components, the GD model-based inversion represents a reliable approach for obtaining stable focal mechanisms in horizontal-vertical DAS monitoring configurations, thereby advancing the application of DAS technology in microseismic monitoring studies.