Numerical investigation of methane and formation fluid leakage along the casing of a decommissioned shale gas well

摘要: Methane and brine leakage rates associated time scales along the cemented casing of a hypothetical decommissioned shale gas well have been assessed with multiphase flow multicomponent numerical model. The conceptual model used for simulations assumes that target formation is 200 m thick, overlain by 750 thick caprock, which in turn 50 surficial sand aquifer, 1000 geological sequence being intersected fully penetrating borehole. This succession units representative region targeted exploration St. Lawrence Lowlands (Quebec, Canada). aimed at assessing impact cementation quality on methane base aquifer. fluids can subsequently lead to contamination groundwater resources and/or, case migration ground surface, an increase greenhouse emissions. minimum reported surface vent (measured level) wells Quebec (0.01 m3/d) as reference evaluate migration. suggest adequately borehole (with annulus permeability kc ≤ 1 mD) prevent over scale up 100 years. However, poorly (kc ≥ 10 could yield aquifer ranging from 0.04 m3/d more than m3/d, depending after abandonment quantity mobile formation. These values are compatible flows simulated travel between few months 30 years, hydrodynamic properties annulus. Simulated long-term years boreholes order 10−5 (10 mL/d) 10−3 (1 L/d). Based scoping calculations well-mixed model, these unlikely major confined since they would only chloride concentration pristine mg/L, significantly below commonly recommended aesthetic objective 250 mg/L chloride.