Despite significant progress, drilling a stable borehole and limiting the failure of the formation surrounding the wellbore remains a significant challenge. Detailed geomechanical analysis, regional structural trends, the distribution of fracture/fault networks, and an understanding of possible stress regimes are necessary inputs to prevent wellbore failures during drilling, field development, and production. To understand the wellbore failures observed in the Pluto gas field located inside the Dampier Subbasin, Northwest Shelf of Western Australia, comprehensive geomechanical modeling is performed on six gas wells, considering local fault orientations, pore pressure, rock failure criteria, drilling direction, and the mud weight design factor. The uncertainties in the input geomechanical parameters for optimum mud weight design are addressed using a stochastic algorithm. In the study area, in situ stress profiles do not match the regional stress profile. Localized stress perturbations and the possible tendency for a transitional stress regime, i.e., reverse to strike-slip faulting regime, exist. The maximum principal horizontal stress (⁠SHmax⁠) orientation follows the local structural pattern rather than the regional SHmax direction. The experimental rock mechanical data of the Muderong shale (the unconfined compressive strength ranges from 5 to 20 MPa, and the internal friction coefficient averaged 0.5), calibrated with an empirical rock-type-based strength formula and recovered core images, suggest the presence of a weak cap rock. A combination of the local stress perturbation, the relatively poor strength of the overlying rock, and the local depositional setting contribute to the observed wellbore failures. Combining the preceding factors, a probabilistic risk analysis approach is developed as a practical solution to ensure safe wellbore planning and reduce drilling costs.

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