Taking the X pad of shale gas in Sichuan Basin as the research object, we observe casing deformation, identify faults, establish a geomechanical model, and analyze the slip probability of faults. The correlational analysis between the positions of the casing deformation and ant tracking faults and microseismic events shows that the fault slip induced by hydraulic fracturing might be the cause of casing deformation. Based on the geological structure of the block, a total of 30 faults are interpreted. The faults were identified mainly by ant tracking and microseismic data. Conventional logs, image logs and mini-fracturing data were analyzed to establish the geomechanical model. The Mohr-Coulomb criterion was used to analyze the activation states of these faults, and the Quantitative Risk Analysis (QRA) method was used to analyze the risk of fault slip and sensitivity of fault slip to each factor.
The results show that most of the faults in this block are in a critical stress state under the in-situ conditions, and the well-oriented faults can easily be activated under current pumping pressure. After a pressure increase of 2500 PSI, the lowest slip probability of the faults intersecting the casing deformation section reaches 65%, which shows that the casing deformation can be caused by fault slip. Sensitivity analysis shows that the results are most sensitive to pore pressure and friction. Based on the risk assessment, the chance of fault slip can be calculated, which provides a reference for guiding drilling design. Hence method may provide an effective method for mitigating casing deformation problems.
