Experimental Investigation of CO2-Brine Simultaneous and Alternate Injection: Implications for Geomechanics and CO2 Storage Capacity

ABSTRACT: To enhance carbon management, the study investigates water-alternating gas (WAG) injection for carbon dioxide (CO2) sequestration in saline aquifers, focusing on its impact on storage capacity. Utilizing core flooding experiments with Gray Berea sandstone and Indiana Limestones at 2500psia confining pressure and CO2 injection at 1100 psi and 100°F to maintain CO2 in a supercritical state, the research compared Continuous CO2 Injection (CCI) and Simultaneous or Alternate Injection of CO2 and Brine (SAI). Findings indicate that CCI and SAI are more favorable regarding increasing storage capacity with SAI, showing a 7.8% porosity increase in sandstone and 11.3% in limestone. However, there is a higher increase in permeability in the case of CCI, which could lead to a higher risk of leakages. SAI demonstrated lower overpressure, suggesting more CO2 can be stored relative to CCI, efficient plume management and enhanced fluid displacement through residual and mineral trapping. This study shows SAI's potential in CO2 sequestration projects, offering insights into brine-assisted strategies for improved storage capacities. 1. INTRODUCTION The escalating levels of atmospheric carbon dioxide (CO2), primarily attributed to fossil fuel combustion and industrial processes, are a significant driver of global climate change (Mouli-Castillo et al., 2021; Tang et al., 2021). This phenomenon poses unprecedented challenges, including extreme weather events, rising sea levels, and detrimental impacts on biodiversity (Hanaoka and Masui, 2020; Napp et al., 2019; United Nations, 2015). In response, CO2 sequestration—capturing and storing atmospheric CO2—has emerged as a pivotal strategy in the global effort to mitigate climate change (Hepburn et al., 2019; Mac Dowell et al., 2017; Zhang et al., 2017). Among the various sequestration techniques, the injection of CO2 into deep geological formations holds promise due to its potential for large-scale storage and the additional benefit of enhancing oil recovery in depleted reservoirs (Global CCS Institute, 2016). Water-alternating gas (WAG) injection is a mature technology developed to improve hydrocarbon reservoirs' oil recovery rates (Afzali et al., 2018; Christensen et al., 2001; Khoshsima et al., 2023). This technique involves the sequential injection of water and gas to maintain reservoir pressure and improve sweep efficiency, thereby maximizing oil extraction production (Aleidan, 2010; AlRassas et al., 2022; Caudle and Dyes, 1958; Rogers and Grigg, 2001; Stephenson et al., 1993; Walker and Turner, 1967; Wang et al., 2023). Given its success in the oil and gas industry, applying WAG injection principles to CO2 storage presents an intriguing opportunity. By alternating between CO2 and water injections, WAG could optimize CO2 storage efficiency, minimize environmental risks, and potentially enhance the integrity of the storage formation.