Identifying Hydrogeochemical Conditions for Fault Self‐Sealing in Geological Storage

Abstract

Injection of anthropogenic CO 2 into a subsurface reservoir will significantly impact the geochemistry, porosity, and permeability of the reservoir. If a fault or fracture penetrates the reservoir, CO 2‐enriched brine may migrate into that fault, eventually sealing it via precipitation or opening it up via dissolution. The goal of this study was to identify and quantify such conditions of fault self‐sealing or self‐enhancing. We found the Damköhler number ( Da) provides a meaningful framework for characterizing the propensity of (fault) systems to seal or open up. We tailored a spatiotemporally varying Da framework and applied it to simplified fault models with eight conditions derived from four geologic compositions and two reservoir conditions. The four geologic compositions were chosen such that three of them were representative of distinct geologic end‐members (sandstone, mudstone, and dolomitic limestone) and one was a mixed composition based on an average of three end‐member compositions. The two sets of P‐ T conditions chosen included one for CO 2 in a gaseous phase (“shallow conditions”) and the other for supercritical phase CO 2 (“deep conditions”). Simulation results suggest that fault sealing via carbonate precipitation was a possibility for shallow conditions within limestone and mixed composition settings. The concentration of cations in the water was found to be an important control on the carbonate precipitation. A key conclusion suggested by the results of this study is that carbonate precipitation in the near‐surface (top 50–100 m) depths of a fault is the most likely mechanism of “self‐sealing” for most geological settings.

Carbon Utilization and Storage through Rehabilitation of Groundwater Wells

“…Depending on the mineralogy of the aquifer, near-well regions may go through dissolution of minerals (especially carbonates), generating wormholes 42 or enhancing preferrential flow pathways like faults and fractures 43 . On the other hand, some of the dissolved CO 2 may precipitate as carbonates in faults and fractures, in deeper subsurface 44,45 as is evidenced in many outcrops 46,47 . Some of the gaseous CO 2 may enter into the vadose zone and the soil.…”

An Improved Tandem Neural Network Architecture for Inverse Modeling of Multicomponent Reactive Transport in Porous Media

“…A significant challenge for developing effective RTMs is parameter estimation, since the existence of large uncertainties associated with reaction processes and the associated parameters in geochemical systems (Ampomah et al., 2017; Dai & Samper, 2006; Fakhreddine et al., 2016; McGrail, 2001; Oyanagi et al., 2020; Patil & McPherson, 2020; Ritschel & Totsche, 2016; Samper et al., 2008; Soltanian et al., 2015; Suescún‐Díaz et al., 2021; Vasco et al., 2018). Measurements of RTM parameters (e.g., selectivity coefficients and initial concentrations of chemical components) are often complicated, time‐consuming, and expensive (Dai & Samper, 2006; T. Xu et al., 1999).…”