Abstract
Summary Depleted hydrocarbon reservoirs repurposed for carbon storage present significant drilling hazards due to altered stress states from years of production. As pore pressure decreases, effective stress increases, narrowing the safe mud weight window and creating conditions for wellbore instability, lost circulation, and caprock fracturing. Subsequent CO2 injection introduces additional thermal stresses that compound these challenges. This study presents a geomechanical framework for assessing drilling hazards in such environments, incorporating three-dimensional stress analysis, coupled thermo-poro-elastic effects, and wellbore stability criteria. Results demonstrate that stress changes vary spatially within and around the reservoir, with uniaxial models proving inadequate near reservoir boundaries where stress arching occurs. Cold CO2 injection induces tensile stresses that further reduce fracture gradients by approximately 0.003 MPa/m. Cyclic pressure loading during intermittent injection operations increases composite permeability by 30–50 percent over 100 cycles. Based on these findings, operational recommendations include performing site-specific three-dimensional geomechanical modeling, locating new injectors away from reservoir boundaries, maintaining precise mud weight control with real-time monitoring, and designing completions with CO2-resistant materials. Integration of these geomechanical principles enables safe well construction for carbon storage projects supporting the energy transition.