Beyond the dots in the box: Microseismicity-constrained fracture models for reservoir simulation

Monitoring induced microseismic events usually results in locations for these events and a geometrical interpretation of these "dots in the box." In this study, we show how additional information obtained from observed microseismic events, namely the source mechanisms, were used to generate a discrete fracture network. Using the wide aperture of a surface star-like array allows inversion for both shear- and nonshear-source mechanisms. Both volumetric and shear-only source mechanism inversion was done on microseismic events from the treatment of a shale gas reservoir in the continental United States. During the same hydraulic fracture stimulation treatment, both dip-slip and reverse faulting sources were active in this reservoir. The source mechanisms revealed fracture orientations more accurately than could be inferred from microseismic event locations alone. The activity of different mechanisms is interpreted as indicating reactivation of existing fractures in the rock, as well as suggesting generation of new fractures.