Investigating Geomechanical Principles of Hydraulic Fracturing Microseismicity Using Stress Inversion and Elastic Dislocation Techniques

Abstract

Microseismic events are commonly used to analyse hydraulic fracture evolution. The combination of seismological and geomechanical modelling techniques will be used to derive activation stresses for discrete populations of microseismic events. A workflow described by Busetti et al. (2014) to distinguish fault planes from auxiliary planes and to derive in situ stress fields for each fracking stage is adapted and modified in order to accommodate elastic properties such as Poisson's ratio, Young's modulus in addition to critical stress criteria. We will present details on how this workflow can be easily performed using the Fault Response Modelling and Stress Analysis modules in Midland Valley's Move™ software. Fault Response Modelling is based on angular dislocation theory with which critical stresses can be calculated by applying a stress state on focal mechanisms derived from microseismic events. Assuming linear elasticity, the magnitude and distribution of fracture-induced stresses can then be calculated and following on from this, slip and dilation tendency as well as fracture stability in the surrounding rock can be determined from shear and normal stresses acting on the stimulated hydraulic fractures. The stress field around hydraulic fractures is altered by each fracking event, and when these fracking events are placed close enough together, the stress shadow effect occurs in which newly created fractures are affected by the stress field from the previous event. The perturbed stress field can be superimposed by the previous in situ stress field within the Fault Response Modelling module, and this technique allows us to investigate the influence of this stress shadow effect. Furthermore, how this technique can be used for hazard investigations, when fault planes are lying in the proximity of the fracking area will be presented. Finally, the influence of pore overpressure due to the fluid injection will be analysed and the effect of stress shadows will be investigated. Busetti S., Wenjie J., Reches Z., Geomechanics of hydraulic fracturing microseismicity: Part 1. Shear, hybrid, and tensile events Shear, hybrid, and tensile events

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016