Microseimsic Signatures of Hydraulic Fracturing: A Preliminary Interpretation of Intermediate-Scale Data from the EGS Collab Experiment 1

Abstract

Microseismic monitoring is widely used to map the development of hydraulic fractures during stimulation of enhanced geothermal, as well as unconventional oil and gas reservoirs. While a prevalent practice is to infer the hydraulic fracture locations and extents based on the locations and shapes of microseismic “clouds”, the occurrences of microseismic events are neither sufficient nor necessary conditions for the presence of a hydraulic fracture at the mapped locations. Definitively establishing the connection between microseismic events and hydraulic fractures is of a great importance. The EGS Collab project offers a unique opportunity to address this problem by enabling microseismic monitoring a short distance (tens of meters) from the events and providing multiple types of measurements and observations to corroborate the inferred fracture location and extents. This work performs a detailed interpretation of the microseismic survey data for the hydraulic stimulation experiments in May 2018. We compare the microseismic event locations to other indications of fracture development to discern the location of the hydraulic fracture with a high certainty. The results suggest that the resolved events were mostly associated with tensile fracturing events. A wide, permeable natural fracture referred to as the OT-P Connector deterred the propagation of the hydraulic fracture upon intersection. The hydraulic fracture bifurcated into two smaller planar features after crossing the OT-P Connector. There is no definitive evidence to support microseismic events generated by shearing of natural fractures.