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Surface microseismic arrays enable long-term field-scale monitoring over multiple stimulations during the life of an unconventional field. In this study, we show highly economic methods of monitoring with sparse surface arrays in the Barnett Shale and develop an alternatative method of processing to enable good vertical and horizontal resolution of located events. We show that sparse surface monitoring arrays enable not only the detection and location of high numbers of microseismic events but also source mechanism characterization. This case study illustrates how hydraulic fracturing activated normal faulting at a distance of approximately 1 mile from stimulated wells. We show that the source mechanism enables us to resolve between newly created hydraulic fractures and activated faults. The differences in source mechanisms and b-values of newly created fractures and activated faults are consistent with independently processed temporary star-like arrays, which are also deployed over the same stimulation.

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We have analyzed the angle-dependent reflectivity of microseismic wavefields at a hydraulic fracture, which we modeled as an ideal thin fluid layer embedded in an elastic, isotropic solid rock. We derived full analytical solutions for the reflections of an incident P-wave, the P-P and P-S reflection coefficients, as well as for an incident S-wave, and the S-S and S-P reflection coefficients. The rather complex analytical solutions were then approximated and we found that these zero-thickness limit approximations are in good agreement with the linear slip model, representing a fracture at slip contact. We compared the analytical solutions for the P-P reflections with synthetic data that were derived using finite-difference modeling and found that the modeling confirmed our theoretical results. For typical parameters of microseismic monitoring by hydraulic fracturing, e.g., a layer thickness of [Formula: see text] and frequencies of [Formula: see text], the reflection coefficients depend on the Poisson’s ratio. Furthermore, the reflection coefficients of an incident S-wave are remarkably high. Theoretical results suggested that it is feasible to image hydraulic fractures using microseismic events as a source and to solve the inverse problem, that is, to interpret reflection coefficients extracted from microseismic data in terms of reservoir properties.