Geological storage is an effective approach capable of reducing greenhouse gases emissions at significant scales by storing the CO2 underground. Subsurface reservoirs with sealing caprocks can provide long-term containment for the injected CO2. However, the leakage is a major concern in most storage sites. The presence of abandoned wells penetrating the reservoir caprock may cause leakage flow paths for CO2 to the overburden. To access the leakage in the subsurface, an analytical model for the time-varying leaky well is needed. In this thesis, we propose a new semi-analytical approach based on pressure-transient analysis to model the behavior of leakage and corresponding pressure distribution in multiple wells multiple layers system. Current solutions either take approximations on essential operations or requires numerical inversion for the solution in the Laplace domain. In this work, we employ the superposition in time and space to solve the diffusivity equation in 2D radial flow to approximate the transient pressure in the reservoirs. We use numerical simulations to verify the proposed time-dependent semi-analytical solution. The results show good agreement in both pressure and leakage rates. Sensitivity analysis is conducted to assess different CO2 leakage scenarios to the overburden. The equivalent injection rate is also proposed to release the single-phase assumption so that the solution can recover identical results as two-phase numerical simulation in the far-field.
|Date made available
|KAUST Research Repository