Geomechanical Considerations in Seismicity Based Reservoir Characterization

Abstract Permeability estimation from microseismic events has been used in the oil and gas industry for more than a decade. However, some of the geomechanical assumptions associated with this technique may not essentially be representative of the field characteristics. Assumptions of shear failure along faults due to any reservoir pressure perturbation and assumption of random distribution of critical pore pressure in a chosen interval as the shear failure criteria presumably will not be representative of the shear failure criteria for the faults. We propose a new model for seismicity based reservoir characterization based on radial fluid flow in the reservoir and Mohr-Coulomb failure criteria which includes the stress state of the reservoir as well as fault friction coefficient (geomechanical reservoir properties) that were not included in the previously published models. This model relaxes some of the assumptions that were associated with former seismicity based reservoir characterization (SBRC) models. We used microseismic data from German Continental Deep Drilling Project (KTB) to test the validity of our new model. The predicted permeability from our model matches very well with the estimated and measured permeability reported values in the literature for KTB. We then performed sensitivity analyses of the effects of fault friction coefficient on estimated permeability, which showed substantial dependency of estimated permeability on fault friction coefficient. This indicates that the dependency of permeability to reservoir geomechanical properties was ignored in previous SBRC models, which is included in our model.