The technology of carbon dioxide (CO₂) enhanced hydrocarbon recovery is favored over other Carbon Capture, Utilization, and Sequestration (CCUS) methods for achieving the “double carbon” goal in China due to its ability to sequester CO₂ geologically while enhancing the recovery rates of oil and gas resources. However, current technologies face significant challenges, such as limited recovery enhancement capacity, as well as high costs and low efficiency in carbon utilization and sequestration. To address these issues, an innovative carbon-negative technology termed Carbon Capture, Circular Utilization, and Sequestration (CCCUS) is proposed. This technology integrates CO₂-microbial enhanced hydrocarbon recovery, CO₂ underground bio-methanation, and CO₂ sequestration in depleted hydrocarbon reservoirs. Compared to conventional CCUS technologies, CCCUS stands out through both its modes of carbon utilization and the forms in which carbon exists, by cyclically biochemically converting endogenous and exogenous CO₂ into renewable natural gas (RNG). A preliminary assessment indicates that CCCUS holds significant developmental potential in China, with 661 million tonnes of CO₂ utilized per cycle and 3.47 billion tonnes ultimately sequestered. However, there is a significant lack of research on the core technology of CCCUS, specifically CO₂ underground bio-methanation, in China. To bridge this gap and mitigate potential challenges during the development of CCCUS, targeted proposals have been formulated. This paper provides new insights into advancing the development of a circular carbon economy and accelerating the achievement of carbon neutrality in China.

In oil and gas well cementing processes, accurately predicting the bottom hole circulating temperature (BHCT) is critical to ensuring effective zonal isolation. Overestimating the temperature can lead to excessive retardation issues, while underestimation can cause cementing accidents. Current methods for calculating the BHCT of cement slurry typically simplify the cementing processes to a single-fluid circulation and ignore the impact of pre-cementing processes on temperature, leading to significant discrepancies between calculated and actual results. In this study, the wellbore and formation are simplified into a two-dimensional axisymmetric structure, and a mathematical model of the temperature field under multi-fluid and multi-step conditions is established based on the law of energy conservation. The finite volume method was used to discretize the model, and a transient temperature field solver for the entire cementing process was developed, which can numerically calculate the temperature of any fluid at any time, any location. For an actual well example, the temperature distribution of the wellbore and formation after casing running is taken as the initial condition. Numerical calculations were performed sequentially to calculate the temperature fields of circulation flushing, wellbore preparation, and cementing, as well as the BHCT of the cement slurry. The study reveals that during the circulation flushing stage, the maximum temperature point in the wellbore is located at a distance of about 366 m above the bottom of the well. In the wellbore preparation stage, due to static heat exchange, the maximum temperature point gradually shifts to the bottom of the well. The BHCT of cement slurry changes continuously under cementing processes with multi-fluid and multi-step, making it a transient value. The BHCT of the lead slurry and tail slurry are not equal, with the maximum BHCT of the tail slurry being 2.46 °C higher than that of the lead slurry. If circulation flushing and wellbore preparation are not considered, the calculated BHCT of the cement slurry will have errors of +6.8% and −1.9%. The study highlighted that considering thermal effects of all cementing stages, such as circulation flushing and wellbore preparation, in BHCT calculations can help improve prediction accuracy.

Amidst the rapid development of renewable energy, the intermittency and instability of energy supply pose severe challenges and impose higher requirements on energy storage systems. Among the various energy storage technologies, the coupled approach of power-to-hydrogen (H₂) and underground H₂ storage (UHS) offers advantages such as extended storage duration and large-scale capacity, making it highly promising for future development. However, during UHS, particularly in porous media, microbial metabolic processes such as methanogenesis, acetogenesis, and sulfate reduction may lead to H₂ consumption and the production of byproducts. These microbial activities can impact the efficiency and safety of UHS both positively and negatively. Therefore, this paper provides a comprehensive review of experimental, numerical, and field studies on microbial interactions in UHS within porous media, aiming to capture research progress and elucidate microbial effects. It begins by outlining the primary types of UHS and the key microbial metabolic processes involved. Subsequently, the paper introduces the experimental approaches for investigating gas–water–rock–microbe interactions and interfacial properties, the models and simulators used in numerical studies, and the procedures implemented in field trials. Furthermore, it analyzes and discusses microbial interactions and their positive and negative impacts on UHS in porous media, focusing on aspects such as H₂ consumption, H₂ flow, and storage safety. Based on these insights, recommendations for site selection, engineering operations, and on-site monitoring of UHS, as well as potential future research directions, are provided.