Comprehensive review of CO2 geological storage: Exploring principles, mechanisms, and prospects

The earth's temperature and climate are being affected by human activities that involve burning of fossil fuels and the clearing of forests, which release the greenhouse gases, like carbon dioxide (CO2). These fossil fuels, include coal and oil, are made of carbon that was first taken from the atmosphere by photosynthesis millions of years ago. The combustion of these fossil fuels is making up >75% of greenhouse gas emissions worldwide and almost 90% of CO2 emissions overall. Additionally, the Global Carbon Budget 2022 estimates that yearly emissions from burning fossil fuels have grown every decade since the mid-twentieth century, from about 11 billion tons in the 1960s to a 36.6 billion tons in 2022. Therefore, carbon capture and utilization (CCU) is considered an important CO2 mitigation strategy to support and compliment carbon capture and storage (CCS) objectives for the reduction and storage of CO2. CO2 geological storage (geo-storage) is a promising approach that can help to reduce greenhouse gas emissions. However, effective storage in geological underground formations requires understanding the main storage techniques and trapping mechanisms. Additionally, more research is required to enhance these techniques and understand their underlying mechanics. In light of this, this research investigates many underground and oceanic CO2 geo-storage techniques, such as saline aquifers, depleted oil and gas reservoirs, unmineable coal seams, basalt formations, and hydrates. The stability of CO2 geo-storage and its many trapping mechanisms are major areas of interest. Physical and chemical processes such as static, capillary, adsorption, solubility, mineral trapping, and ionic exchange are highlighted. Results from field research and experiments show how CO2 geo-storage technology is becoming more useful. The discussion of this review article provide observations on the future prospects and economic opportunities of CO2 geo-storage, underlining its transformative potential in combating climate change. By 2030 or late, most of the countries are actively working to increase their CO2 storage capacity. These efforts include initiatives such as additional funding, regulatory frameworks, and CCUS projects aimed at increasing their potential storage capacity. Concisely, this comprehensive review provides guidance for researchers, policymakers, and those in the industry; as understanding CO₂ geo-storage can pave the way for the development of more efficient, sustainable, and safe storage techniques, thus potentially playing a crucial role in addressing the challenge of global climate change. This review is divided into four parts: (1) an overview of the principles of CO2 geo-storage, (2) an examination of trapping mechanisms for CO2 geo-storage, (3) an analysis of experimental and field studies on CO2 geo-storage, and (4) exploration of the prospects for CO2 geo-storage.