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Characterizing Tri-linear Deformation for Hydraulic Fracture Stimulations Utilizing Microseismicity


Microseismic events observed during hydraulic fracturing can be considered as a sudden inelastic deformation (fracturing and frictional sliding) within a given volume of rock that radiates detectable seismic waves. Standard processing of recorded waveforms provides information related to the source of the seismic radiation such as time, location, seismic moment, and fracture size. Enhanced processing of the outcome provides information on seismic energy and stress release estimates. Having processed clusters of microseismic events, we can quantify the changes in the seismic strain and stress regime and rheological properties of the rockmass associated with the seismic activity. This aggregate behavior can be captured through the use of dynamic parameters, such as Plasticity Index, Diffusion Index, Stress Index, and Seismic efficiency. All of these parameters are related to the rockmass resistance to coseismic inelastic deformation (dynamic friction of the ruptures) within a volume of interest over time which help us to have a better understanding of the ease with which the reservoir deforms within a tri-linear model. This analytical model divides the frac'ing induced deformation into three regions of dominant fracture conductivity due to stimulation, region of enhanced stimulated permeability due to presence of natural fractures, and unstimulated region. Integrating the dynamic parameters with other geophysical data sets recorded prior, during, and post-frac'ing such as well logs, seismic attributes, chemical tracers, and production data leads to the development of a more representative model of the complex rock-mass behavior, which provides an opportunity to optimize stimulation programs and improve future production in such resources. In this study, we use the dynamic parameters to investigate the seismic stress and strain variations of a Permian unconventional reservoir in response to hydraulic fracturing process. We use these parameters to optimize the measurements of stimulated reservoir volume and effective fractured-zone dimensions by taking into account the nature of deformation associated with microseismic activity. Furthermore, integrating our results with available well logs offer valuable insight into the nature of near and far-field rockmass deformation.