AAPG Annual Convention and Exhibition

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Mapping Reservoir Stress Conditions Using Hydraulic Fracturing Microseismicity


Focal mechanisms, when computed for an entire microseismic catalogue, permit a rapid assessment of the states of stress throughout the stimulated reservoir. The potential for a fracture to fail depends on its frictional resistance and orientation within the prevailing stress field. Previous studies have demonstrated that the most hydraulically conductive fractures have the highest failure potential (i.e. highest shear to normal stress ratios). We present a structural analysis workflow using microseismic focal mechanisms to investigate the dynamic response of the reservoir during and after stimulation. Focal mechanisms are derived using full waveform fitting techniques, and the ambiguity in identifying the true fracture plane is resolved by simply choosing the nodal plane that aligns with the developing hydraulic fractures. A global stress inversion of the fracture plane solutions is done to estimate the orientations and relative magnitudes of the principle stresses. Friction laws are then used to constrain for each event a suite of geomechanical parameters (failure potential, dilation tendency, and excess pore pressure) in order to identify fracture populations likely to control fluid flow, those that required different stimulation pressures in order to contribute to flow, and the mechanical conditions that favored out-of-zone growth and reactivation of geohazards. The method is applied and discussed in the case of a microseismic event catalogue obtained during the stimulation of two horizontal wells landed in the Eagle Ford, where large variations in event densities as well as geohazards were observed. We will also show examples from other plays to demonstrate that this workflow is applicable to all plays.