An analytical model to determine a reservoir capacity for wastewater disposal with consideration of geomechanics and extractions

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ABSTRACT: Reservoir capacity in injection wells depends on size, compressibility, and the maximum allowable pressure before risking formation integrity. Studies link saltwater disposal (SWD) operations to fault reactivation, while permeability, reservoir fluid properties, and mineralogy also influence subsurface response. Geomechanical effects, including poroelastic and thermoelastic stress changes, complicate reservoir behavior and must be carefully considered in SWD design. This study presents an analytical approach to determine the maximum injection volume and pressure constraints using pressure superposition principles. The model assumes a homogeneous reservoir with infinite-acting, open, or closed boundaries and multiple wells, operating at a constant rate. A geomechanical framework estimates fracturing pressure gradients by considering in-situ stress changes, rock properties, and thermal effects of cold-water injection. The study assesses pressure evolution in sensitive regions to ensure safe injection and prevent formation damage. Applied to a mature hydrocarbon-producing region with 274 wells, including plugged and abandoned (PA) wells from the 1940s to 2024, it uses pressure superposition to estimate average reservoir pressure and identify sensitive areas. The maximum sustainable injection capacity is determined by combining statistical reservoir characterization with geomechanical constraints. This approach optimizes SWD design, monitors injection pressures, and ensures reservoir integrity.

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