ON MICROSEISMIC EVENTS ASSOCIATED WITH FLUID-FILLED FRACTURE PROPAGATION IN CLOSE PROXIMITY TO A NATURAL FAULT

Liquid-filled fractures are actively created in the Earth’s subsurface for stimulation of enhanced geothermal systems and tight shale gas reservoirs. How these tensile fractures propagate in the presence of faults and how the fracture’s growth affects reactivation of the fault is not widely understood. Determining the geomechanical interaction between the fractures propagation and the fault’s reactivation contributes to our understanding of how fault reactivation may occur during hydraulic fracturing, i.e. does the fracture’s growth induce slippage along the fault or diverts into the fault and causes further slippage and opening along the fault.

Microseismic events from a multi-stage hydraulic fracturing treatment in the Barnett Shale have been selected with varying distances from a known fault zone. Occurrence of microearthquakes in this fault zone may indicate fault reactivation. Using moment tensor inversion to determine the source mechanisms of these microearthquakes would help us to understand fracture behavior in this situation while limited access to the subsurface doesn’t leave another tool to study this problem. Preliminary results indicate that the microearthquakes primarily result from opening failure mechanisms throughout the stimulation. The objective is to identify a relationship between fluid-filled fracture propagation and reactivation of slippage along a natural fault by analyzing the change in the failure mechanisms with increasing proximity to the faulted zone.