Application and Optimization of CCUS Technology in Shale Gas Production and Storage

Global climate change is a crucial issue confronting the international community. The greenhouse effect caused by CO₂ emissions is widely recognized as one of the key factors impacting climate change [1,2,3,4]. Reducing CO₂ emissions and fully utilizing CO₂ are important ways to protect the environment and achieve resource development. Carbon dioxide capture, utilization, and storage technology (CCUS) is an emerging technology with the potential to result in large-scale CO₂ reduction; therefore, it has received widespread attention both domestically and internationally in the past decade. For example, the United States Department of Energy released the Carbon Dioxide Capture and Storage (CCS) Technology Research and Development Demonstration Roadmap in 2010, which laid out a development path for CCS and focused on efficient and economical solutions to quickly realize commercial applications. CCS technology needs to overcome various challenges at the economic, social, and technological levels, including the effective monitoring and verifying of CO₂ storage processes and the viability of the permanent underground storage of CO₂. The development of the Canadian CCS Technology Development Roadmap (CCSTRM) underwent four stages: situation analysis, confirmation of technology paths and R&D strategies, confirmation of priority directions for R&D and demonstration, and final writing. Japan’s CCS research is basically synchronized with European and North American countries. In Japan, CCS technology was implemented in 2020, and encompasses various applications such as enhancing oil recovery using CO₂, sealing CO₂ up to saltwater layers, injecting CO₂ into depleted natural gas fields and coal seams, and developing CO₂ transportation technology. The goal in China is to achieve peak CO₂ emissions by 2030 and carbon neutrality by 2060 through stronger policies and measures. This further emphasizes the concept of “turning waste into wealth”, and emphasizes opportunities to improve the recovery rates of oil, natural gas, coalbed methane, and water using carbon dioxide (CO₂-EOR, CO₂-EGR, CO₂-ECBM, and CO₂-EWR, respectively) [5].

Natural gas resources in unconventional sedimentary reservoirs, such as shale and coal seams rich in kerogen, are abundant and environmentally friendly, making them one of the most important energy resources available [6,7,8,9,10,11]. CO₂-enhanced shale gas production and underground storage integration technology are important ways to apply CCUS. Because of its characteristics of energy conservation, emission reduction, and efficient exploitation of shale gas, CCUS is emerging as an important future means for efficient shale gas exploitation and development [3,12,13]. At the same time, the stability of shale reservoirs is also a focus of research, directly determining the safety and efficiency of mining. The failure criterion that fully considers shale anisotropy and hydration is an important factor in evaluating the stability of shale formations [14]. The continuous exploitation and use of shallow shale gas is causing shale gas exploration and development to gradually move to deeper locations. These deeper environments have complex and changeable geological conditions, high temperatures, high ground stress, fluid seepage pressure, and other complex conditions [15,16,17,18,19,20,21]. This makes innovations in applying CCUS technology during deep shale gas exploitation urgent. CCUS application in deep shale gas exploitation is now an important research direction.

Scholars have studied shale pore structure, shale gas recovery, shale reservoir stability, and shale gas movement and transmission in the application of CCUS in shale gas exploitation. For example, Wang et al. [22] analyzed the displacement mechanism of CH₄ in nanoporous shale, its positive and negative effects on solid storage and organic matter extraction, the migration and expansion processes of elements, and the macro- and micro-control mechanisms for improving reservoir permeability. Feng et al. [23,24] studied the fracture trajectory of shale in the Longmaxi Formation after failure, and explored the mechanical properties of the shale under supercritical CO₂ adsorption conditions. Asif et al. [25] measured the isotherms of two gases (CH₄ and CO₂) at pressures up to 8.4 MPa, and constructed an isotherm of CO₂ to estimate the enhanced recovery rate of coalbed methane. Kong et al. [26] studied auxiliary additives to improve shale oil and gas production. Chen et al. [27] studied the creep characteristics of shale, considering the influence of bedding direction and water content.

The application of CCUS in shale gas production and storage involves many aspects, including in-depth research on its mechanisms and key technologies. This includes the competitive adsorption mechanism of CO₂/CH₄ in shale, SC-CO₂ displacement and the displacement of shale gas, the SC-CO₂ storage mechanism, SC-CO₂ jet technology, SC-CO₂ fracturing technology, the CO₂ displacement of shale gas, and SC-CO₂ storage technology. These issues need to be analyzed and solved from the perspectives of technology, security, investment, environment, and ecology. Therefore, we have organized this Special Issue of Energy, titled “Application and Optimization of CCUS Technology in Shale Gas Production and Storage”. This Special Issue welcomes contributions of all achievements regarding CCUS technology related to shale gas, including all outlines from laboratory experiments, numerical simulations, engineering evaluations, and economic judgement.