Estimation of Fault Slip Potential Resulting From fluid Injection

We present a methodology that applies Quantitative Risk Assessment to calculate the probability of a fault exceeding Mohr-Coulomb slip criteria. The program utilizes fault strike and dip, injection well locations and rates, hydrologic parameters and stress state inputs. Faults can be randomly generated, or imported. First a deterministic, then a Monte-Carlo Mohr-Coulomb analysis is run on each fault. The former produces the minimum pore pressure to slip on the fault, and the latter produces the probability of the fault slipping, as a function of pore pressure increase. Next a simple radial flow model estimates the pore pressure increase resulting from injection, however it is also possible to import a more complex hydrological model. When integrated with the probabilistic geomechanical analysis, the probability of the fault slipping as a function of time is produced. Utilization of the model requires constraining fault geometry, the state of stress and the pore pressure perturbation associated with injection. The strength of this approach is that uncertainties in relevant parameters can be propagated through the analysis. An obvious limitation of the model is that it can only assess the probability of slip on known faults in response to a predictable pore pressure perturbation. The program will be freely available for use online.