Modeling CO2 Sequestration Using a Sequentially Coupled 'Iterative-IMPEC-time-split-thermal' Compositional Simulator

This paper presents an efficient numerical scheme for multiphase compositional flow coupled with subsurface heat transfer. The flow equations are first presented followed by a brief discussion of the equation of state (EOS) and a description of the two-phase flash algorithm. An implicit-pressure, explicit-concentrations (IMPEC) sequential algorithm is then applied iteratively to enforce the non-linear volume balance saturation) constraint. The pressure equation is solved using mixed FEM, while the concentrations are updated consistent with requiring local mass balance of every component. Thermal effects also play an important role in such problems since they effect the phase properties and hence, stable and accurate locally conservative methods are desirable to model the thermal energy balance equation. To this end, we present also a time-split scheme for modeling the energy balance equation that is sequentially coupled to the flow solution rendering it cheap yet accurate for the complex problems being modeled. Results of benchmark problems in compositional flow modeling are presented and validated where possible. Some large-scale parallel tests are performed on more challenging applications such as those with highly heterogeneous permeability fields on very fine grids. Efficient parallel scalability of the code on upto 512 processors is also demonstrated. Finally, some test cases simulating "real world" problems of CO2 sequestration in deep saline aquifers are presented. Initial results show reasonably good agreement of CO2 plume shapes, arrival times, leakage rates and production curves with semi-analytic solutions, wherever available. All computations were carried out within the IPARS-CO2 code base framework.