A geochemical compositional simulator for modeling carbon dioxide sequestration in geological formations.

摘要

Geological storage is one of the key technologies for reducing anthropogenic emissions of CO2. However, if this technology is to be implemented safely, efficiently, and predictably, the knowledge of the geology, geophysics, and geochemistry of CO2 storage must be refined. When CO2 is injected into geological formations, various physical and geochemical trapping mechanisms would prevent the CO2 from escaping to the surface. The simulation of CO2 injection will help us to understand the behaviors of CO2 and other components during the whole process and to assess the storage capacity of target formations and the leakage risk of CO2.;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. The reaction option available in the model is able to handle complex geochemical systems. 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. A new solution method is implemented to make the model more suitable to solve problems in complex geologic formations with complex geochemistry models. A novel parallelization scheme for domains with complex fracture systems is also described.;The model is verified using analytical solutions and benchmarks. A variety of applications are demonstrated. The CVFEM-based discrete fracture network 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. It is shown that this fracture representation is essential in correctly modeling the rapid and oftentimes uneven migration of CO2 to the seal. Meanwhile. hysteresis effect in CO2 sequstration is examined to show the residual trapping mechanism, and the performance of parallel computation is evaluated.;In summary, successful completion of this project will result in the creation of a parallel and modularized simulator that can address the CO 2 sequestration process in highly complex fractured geological systems.;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).