Numerical investigation on effect of varying injection scenario and relative permeability hysteresis on CO2 dissolution in saline aquifer

Abstract

In subsurface storage of CO2 in saline aquifer, dissolution trapping is presumed to be the most feasible trapping mechanism that ensures storage safety by initial immobilization of injected buoyant CO2. Time span for this natural mechanism is, however, spanning in terms of decades. Accelerating the rate of dissolution by imposing various reservoir engineering principles is the peer area of research interest. Though dissolution of CO2 depends on pressure of the system, pressure buildup during injection process could potentially create or activate fractures, providing migration pathways for buoyant CO2 that questions safety of storage. Attempt has been made in the present paper to understand the impact of various injection scenarios, such as water alternate gas (WAG), intermittent and intermittent WAG injection scenario, toward enhancing dissolution rate with associated minimal effect on pressure buildup. Numerical model conceptualizing immiscible two-phase flow has been developed. Effect of hysteresis of relative permeability has been considered, and solubility of CO2 in brine is computed using developed thermodynamic model. An enhanced dissolution rate of about 68 % has been observed in case of WAG scenario, however with associated disadvantage on drastic borehole pressure buildup. On the contrary, lesser borehole pressure buildup has been observed in intermittent injection case, while dissolution rate is significantly lesser when compared with WAG process. Interestingly, it has also been inferred from present study that intermittent WAG process plays a crucial role in eliminating the primary disadvantages of WAG and intermittent process with promising enhanced dissolution rate than WAG and intermittent processes.