Modeling the Spatial and Temporal Evolution of Fractured Systems with a Heterogenous Mineralogy

Abstract

Reactive transport modeling is a critical tool for elucidating the coupling among geochemical reactions, transport processes, and fracture permeability. This study explores the implications of preferential clay-rich regions near fracture surfaces of a Mancos shale sample on the reactive evolution of the fracture by using reactive transport simulations. These simulations utilized heterogeneous mineralogy data obtained from an in-depth analysis of a clay-rich region near the fracture surface, sourced from a mechanically induced fracture. We compared these simulations with counterparts assuming homogeneous mineral distributions based on bulk X-ray diffraction (XRD) data and prior imaging of the sample matrix. The results consistently show increased reactivity in cells near the inlet and fracture surface across all scenarios. The most significant changes in the porosity, mineral composition, and ion concentration occur in cells adjacent to the fracture at the system inlet. Comparative analysis reveals variations in mineral and porosity evolutions among the three systems. Over longer simulation periods, dissolution and porosity increase occur more rapidly in simulations, reflecting mineral heterogeneity, particularly within the clay-rich region near the fracture. A sensitivity analysis of mineral surface area (SA) values shows consistent trends using both low and high Brunauer−Emmett−Teller (BET) SA values over short time scales (days) but substantial disparities over longer time scales (years). These findings hold promise for improving our ability to predict the evolution of reactive fractures, with implications for subsurface CO 2 sequestration and oil recovery. In summary, this study advances our understanding of reactive transport in fractured systems, offering new avenues for predictive modeling.