Petrophysics is a core component of subsurface characterization and monitoring design for carbon capture and storage (CCS). In the United States, Environmental Protection Agency (EPA) underground injection control (UIC) rules for carbon storage (class VI wells) include subsurface characterization, CO2 plume stabilization, Area of Review (AoR) modeling, and monitoring during pre-injection, injection, and post-injection, where petrophysicists can play important roles. We discuss some important petrophysics-related questions and their significance relevant to CO2 storage and plume migration using simplified reservoir simulation models and show examples from three petrophysical case studies in Miocene and Wilcox formations on the Gulf Coast, Texas and fractured Trenton-Black River group in Michigan. The simulations provide a first-principle understanding of CO2 plume migration and controlling factors that petrophysicists can analyze.
Over the last two decades, several CCS demonstration projects have been completed around the world (including US, Canada, Norway, Australia, and Japan), some of which were successful in showing the feasibility of CO2 storage in the saline aquifer and depleted reservoirs (Furre et al., 2017; Gupta et al., 2020; Hovorka et al., 2013). Recently, Global CCS Institute (2022) provided a comprehensive status update on CCS facilities in different operational and development stages around the world. These studies have indicated that we need a large injection reservoir (or stacked reservoirs) with sufficient pore space, reservoir connectivity, and injectivity that can accept commercial rate and volume of CO2 injection over time as well as a confining system overlying the entire AoR to prevent vertical migration of CO2 [AoR represents the region that may be affected by the injection of CO2; please see Directive 2009/31/EC, 2009; US EPA, 2011; ISO/TC265, 2017 for details on regulatory definitions]. These projects also facilitated the transfer of certain oil and gas knowledge, technologies, and workforce to CCS. However, most of these demonstration projects to date have largely been first-of-a-kind and isolated in nature (Bump and Hovorka, 2023). Some of these projects had a small areal extent and collected a significant volume of petrophysical logs and core data from a very limited number of wells for high-resolution site-specific modeling, storage capacity estimates, and monitoring. This approach is not always beneficial to offer a broad systems-level understanding of the petrophysical requirements and solutions for carbon storage-related subsurface characterization and monitoring. Site-specific CCS approach has been myopic in some sense that it has not always yielded deep geologic insights into the basin-wide understanding of reservoir connectivity, CO2 injectivity, and sealing capacity.
