Characterizing Dynamic Fracture Growth and Azimuth using Seismic Moment Tensor Inversion Analysis of Microseismicity

Abstract

Abstract Based on traditional fracture models it is generally considered that fractures develop along a single fracture azimuth or along a plane of fracturing controlled by regional stresses (along the maximum principle stress direction), even within the context of a three-dimensional fracture network. Recently, the utilization of distributed geophone arrays around treatments has provided for an opportunity to investigate the way these fractures develop by examining the microseismic events recorded during a stimulation, utilizing a Seismic Moment Tensor Inversion (SMTI) approach. SMTI provides additional information on the events beyond location and magnitude, such as the relative contribution of isotropic versus shearing components of failure, the potential fracturing plane orientations and the localized strain axes responsible for the failures. Additionally, SMTI data can be further used in Deformation State Analysis (DSA) to define the stress-strain field responsible for the growth and development of the hydraulic fracture. In this study, we examined microseismicty associated with an open-hole completion program in a tight sand formation in North America. We observed that the DSA-derived localized stress-strain field was perturbed by the stimulation program, being highly variable both spatially and temporally. The results further suggest that fractures progress in a complex system of both macro- and micro-fractures containing several different azimuths, with progressive growth occurring as a result of stress shedding to adjacent fractures or zones of weakness. This localized fracturing behavior led to the development of an interconnected fracture network, which resulted in hydraulic fracture growth in the direction of the regional maximum horizontal shear stress.