Pore Scale Methods to Enhance Understanding of Geochemical Reaction Rates in Porous Media

Abstract

Geochemical reactions play an important role in subsurface systems such as in contaminant fate and transport, chemical weathering and geologic carbon sequestration. These reactions, mainly dissolution/precipitation, will potentially alter formation properties including porosity and permeability. The rate and extent of these dissolution/precipitation reactions depends on the properties of the porous media such as mineral distribution, reactive surface area, flow rate, and the pore network structure. However, there is a large gap between observed field and laboratory or simulated reactions rates. This is in part due to the over/under estimation of parameters such as mineral accessible surface area, differences in reaction conditions chemical impurities and coupled reactions. Understanding the importance of these parameters is largely attributed to the heterogeneity of the samples particularly at the pore scale. This thesis explores two methods to improve understanding, and thus estimation, of reaction rates in porous media systems in the context of prospective geologic CO2 storage in the Paluxy formation in Kemper County, MS (Project ECO2S). First, additive manufacturing or 3D printing with custom reactive filaments is explored as a means to mimic the reactive properties of real rocks. Filaments are used to fabricate synthetic rocks based on the pore structure of a sandstone sample obtained from a 3D X-ray computed tomography (X-ray CT) image. The distribution and accessibility of the reactive minerals in the printed samples is then evaluated using 2D and 3D imaging. Second, direct numerical simulation is used to simulate three-dimensional flow and transport of ions at the pore scale using OpenFOAM in the pore-mesh of a sandstone sample obtained from a 3D X-ray CT images. The Navier-Stokes and continuity equations are used for simulating flow and the transport of ions is simulated using the advection-diffusion equation. The simulation results, along with a new library to calculate rates of reaction and mesh motion as well as relaxation, will form the basis of a dynamic, multi-mineralic pore-scale reactive transport model.