Multiphase flow dynamics during CO₂ disposal into saline aquifers

Abstract.

Injection of CO₂ into saline aquifers is described by mass conservation equations for the three components water, salt (NaCl), and CO₂. The equations are discretized using an integral finite difference method, and are solved using methods developed in geothermal and petroleum reservoir engineering. Phase change processes are treated through switching of primary thermodynamic variables. A realistic treatment of PVT (fluid) properties is given which includes salinity and fugacity effects for partitioning of CO₂ between gaseous and aqueous phases. Chemical reactions and mechanical stress effects are neglected. Numerical simulations are presented for injection of CO₂ into a brine aquifer, and for loss of CO₂ from storage through discharge along a fault zone. It is found that simulated pressures are much more sensitive to space discretization effects than are phase saturations. CO₂ discharge along a fault is a self-enhancing process whose flow rates can increase over time by more than an order of magnitude, suggesting that reliable containment of CO₂ will require multiple barriers.