Optimizing CO2 storage in deep saline formations: a comprehensive review of enhancing pore space utilization through simultaneous or alternate aquifer injection

Deep Saline Formations (DSFs) are increasingly recognized for their significant role in geological carbon dioxide (CO₂) storage, a crucial part of Carbon Capture and Storage (CCS) strategies aimed at mitigating climate change. Nevertheless, formation overpressure, capillary breakthrough pressure, and injectivity impairment often compromise the actual CO₂ Storage Efficiency (CSE) in these formations, potentially reducing storage efficiency by up to 22%. However, comprehensive knowledge of Pore Space Utilization (PSU) in CO₂ storage in deep saline formation must be improved to address this inefficiency. This study presents a first-of-its-kind work combining a comprehensive review with a proposed innovative concept on the viability and effectiveness of the Simultaneous or Alternate Aquifer Injection (SAI) method to enhance CO₂ storage within DSFs. Further, a conceptual future direction for optimizing CO₂ storage in deep saline formations was proposed. We introduced the Simultaneous or Alternate Aquifer Injection (SAI) as a useful approach to optimizing PSU and CSE in DSFs. This method is similar in principle to Water Alternating Gas (WAG) used in CO₂-EOR. While there is a lack of data on the SAI process, WAG data shows that incremental CO₂ is stored in a reservoir when water is introduced in a CO₂-EOR, thereby increasing the oil recovery and CO₂ storage. This incremental ranges from 3–100% CO₂ stored in a formation. The SAI method can enhance CSE by approximately 25% on average compared to traditional injection methods when using this as an analog. Our study further highlights the complexities of the SAI method and its potential to enhance storage efficiency and capacity, which is crucial for large-scale CCS implementation. We compared various trapping mechanisms, their impacts on CSE, and how they can be potentially augmented through the SAI to increase PSU in saline aquifers to mitigate climate change. The SAI method, involving simultaneous or alternate injection of CO₂ and brine, may yield a novel approach to managing the movement of the CO₂ plume in the aquifer reservoir, thereby maximizing storage efficiency and minimizing leakage risks. While our review of the SAI method shows promise, it still poses technical, regulatory, and economic challenges. Our review findings emphasize the need for more integrated dynamic modeling, numerical simulations, and sensitivity analyses for successful implementation. With adequate experimental and simulation support, the SAI approach has the potential to revolutionize CO₂ storage operations in DSFs, contributing significantly to global net-zero carbon emission goals.