Revolutionizing Fault-Stability Analysis: A Novel Approach to Managing Uncertainties in Unconventional Assets and Hydraulic Fracturing Stages Placement Optimization

Abstract The article presents a novel methodology for unconventional assets to determine fault stability while managing uncertainties. This approach is crucial for initial state, drilling conditions, and hydraulic fracture operations. It covers the initial stages at the field scale with high uncertainty in stresses and fault geometries to the PAD scale, where the main uncertainty lies in fault parameters. Initially, stress state, rock properties, and fault geometry in an area have high uncertainties that are reduced during field development. An application software/tool was developed to evaluate fault stability under different scenarios of pressures. This tool identifies areas of greater risk of casing damage. At the PAD level, uncertainties in target geometry, stress state, rock properties, and fault geometry are reduced, but fault parameters (mainly friction angle) remain uncertain. A second tool was developed to determine the sliding probability of faults crossed in a well-pad. The play has 3 distinctive pay zones/shale formations: upper, middle, and lower, confined by much higher strength formations above and below. The above formation, the upper-hard formation, is weak and highly stressed. The area of study did not have any data for a full anisotropic characterization; however, there was production data suggesting the connectivity in the staggered lateral wells. There is evidence of fault reactivation in the area due to leaks through the faults located in the weak and stressed formation where wells initiate the curvature, the heel section. Also, microseismic activity aligned with fault locations indicates some fault reactivation. The regional study was performed with the in-house developed methodology, locating high-risk areas in natural conditions, drilling pressures, and hydraulic fracturing (HF) conditions. At the pad level, a study example result is detailed in this paper. Stress-state was defined from pilot 1D Geomechanical Models, the formation tops surfaces, regional strains were applied, and rock properties were populated. Regarding fault properties and the impact on stability, the dip and the friction angle are the parameters with the most impact on stability. Montecarlo simulation with a range on friction angle was implemented in the example calibrated with an example of casing failure due to a fault reactivation in an HF operation. The results were used to change trajectories if the probability of sliding in the initial state or drilling conditions when solving the issues or reducing/avoiding some stages due to possible fault reactivation if a tip of a fracture arrives to a fault with high risk in fracture closure pressures in the injection fluids at the tip. Traditional workflows address uncertainties with independent variables. However, the field scale proposed methodology introduces a groundbreaking approach by managing uncertainties with all dependent variables, setting a new industry standard. Additionally, The application of the proposed methodology to the pad compared with a traditional code based on limit equilibrium method and only uncertainty in fault friction angle is presented, jointly with the proposed methodology theory. A precise 3D geomechanical model was performed to compare both methodologies, making it a powerful asset in the field.