(389e) A FULLY COUPLED GEOCHEMICAL COMPOSITIONAL SIMULATOR for Modeling CO2 Sequestration in Formations with Discrete Fault/Fracture Networks

A geochemical coupled compositional model is developed to describe the complex processes during CO2 sequestration. The model is built on a modularized framework that allows coupling different discretization schemes with simulations of different physical processes. The modular approach allows the use of different spatial discretization methods including control-volume finite element method (CVFEM), standard finite difference method (SFD) and a generalized finite volume method (FVM). The coupled geochemical compositional model is capable of handling multi-phase and multi-component reservoir problems. The reaction option available in the model is able to handle complex geochemical systems. A new solution method is implemented to make the model more suitable to solve problems in complex geologic formations with complex geochemistry models. Natural variables are chosen as primary variables for their simplicity. Variable substitution and a novel equation alignment technique are required to correctly handle phase change, which is very common in the different phases of the CO2 sequestration process. For maximum numerical stability, a fully implicit scheme and an analytical Jacobian matrix are used, and all equations are solved simultaneously in the simulator. Gaussian elimination is applied twice before the solution of the linear equation system, first to eliminate equilibrium reaction rates and then to reduce the size of the linear system. The model is verified using analytical solutions and benchmarks. It is shown that a DFN representation is essential in correctly modeling the rapid and oftentimes uneven migration of CO2 to the seal. The DFN approach also facilitates modeling critical aspects of fault reactivity (dissolution) which may lead to seal breaches. A novel parallelization scheme for domains with complex fracture systems is also described. The CVFEM-based method is used for the first time to analyze the impact fault/fracture networks may have on the integrity of storage in the CO2 sequestration process.