Bedding-plane slip as a microseismic source during hydraulic fracturing

Abstract

Microseismic source mechanisms in shales often show similar double-couple events with one vertical nodal plane aligned with the hydraulic fracture and the other nodal plane oriented horizontal. We interpret the horizontal nodal plane as the fault plane where the shearing represents bedding-plane slip driven by opening of a connected, vertical hydraulic fracture. Using precisely mapped microseismic source locations from a Barnett shale hydraulic-fracture completion, Rutledge et al. (2015) proposed a model of step-over or jog structures along bedding to describe bedding plane slip and sense-of-slip reversals driven by vertical fracture opening. However, common step-over features will usually be too small to create a detectable microseismic signal, and if large, will terminate vertical growth. Chuprakov and Prioul (2015) describe a model of hydraulic-fracture growth through weak bedding interfaces where tensile crack growth can arrest at interfaces encountered. Fluid invasion and pressure can weaken the interface which can then shear from the added stress of adjacent crack opening. Under certain conditions, with subsequent net pressure recovery and gain, tensile fracture propagation can continue across the interface. Invoking this model, at least qualitatively, makes a more consistent explanation of the continuity and time-space development of the microseismic structures, as well as explaining the observed patterns of shear-fracture first motions. Presentation Date: Tuesday, October 18, 2016 Start Time: 10:20:00 AM Location: 144/145 Presentation Type: ORAL