STOMP-ECKEChem: An Engineering Perspective on Reactive Transport in Geologic Media

ECKEChem (Equilibrium, Conservation, Kinetic Equation Chemistry) is a reactive transport module for the STOMP suite of multifluid subsurface flow and transport simulators that was developed using an engineering perspective. STOMP comprises a suite of operational modes with capabilities for a variety of subsurface applications (e.g., environmental remediation and stewardship, geologic sequestration of greenhouse gases, gas hydrate production, and oil shale production). The ECKEChem module was designed to provide integrated reactive transport capabilities across the suite of STOMP simulator operational modes. The initial application for the ECKEChem module was for the simulation of mineralization reactions that were predicted to occur with the injection of supercritical carbon dioxide into deep Columbia River basalt formations, using STOMP-CO2 which solves sequestration flow and transport problems for deep saline formations. The STOMP-ECKEChem solution approach to modeling reactive transport in multifluid geologic media is founded on an engineering perspective: 1) geochemistry can be expressed, input and solved as a system of coupled nonlinear equilibrium, conservation and kinetic equations, 2) the number of kinetic equation forms used in geochemical practice are limited, 3) sequential non-iterative coupling between the flow and reactive transport is sufficient, 4) reactive transport can be modeled by operator splitting with local geochemistry and global transport. This chapter describes the conceptual approach to converting a geochemical reaction network into a series of equilibrium, conservation and kinetic equations, the implementation of ECKEChem in STOMP, the numerical solution approach, and a demonstration of the simulator on a complex application involving desorption of uranium from contaminated sediments.

Keywords: Equilibrium, conservation, kinetic equations, operator splitting, reaction network translation, numerical Newton-Raphson iteration.