This paper is the result of comprehensive geological survey engineering of carbon peak and carbon neutrality.

Objective To achieve the carbon neutrality, the carbon dioxide geological storage in saline aquifers is considered as the bottom technology in the field of fossil energy in China. With the increasingly extensive and in-depth research on the evaluation of storage potential at different geological scales, it is urgent to establish a unified classification system and scientific evaluation methods for storage potential.

Methods This paper refers to the geological exploration experience of solid minerals, oil and gas minerals, as well as the potential levels and evaluation methods of saline aquifer carbon dioxide storage at home and abroad. It divides the stages and potential levels of saline aquifer carbon dioxide storage in China, and proposes potential evaluation ideas, calculation formulas, and important coefficient values for reference.

Results Firstly, by setting four stages of the requirements for exploration and geological understanding of the storage sites, i.e. general exploration, detailed exploration, advanced exploration and injection, the carbon dioxide storage potential is divided into four levels: geological potential, technically capacity, technically-commercial capacity and engineering reserves. The general exploration stage corresponds to the possible level (Level D), the detailed exploration stage corresponds to the probable level (Level C), the advanced exploration stage corresponds to the proved level (Level B), and the injection stage corresponds to the engineering level (Level A). Secondly, the assessment on carbon dioxide storage potential can be carried out in process of reservoir selection, potential grading and calculation, and the effective reservoirs should be selected considering storage conditions, sealing ability, stability of storage complex, and development of deep resources. At last, for different levels of carbon dioxide storage potential calculation, formulas of volume method or mechanism method, as well as geological coefficient, displacement coefficient, cost coefficient and other key parameters should be reasonably selected according to the application scenarios. The carbon dioxide storage potential should be assessed using numerical simulation with different injection schemes in the detailed exploration stage.

Conclusions The potential assessment on carbon dioxide storage in saline aquifers should include a multi-scale and multi-level dynamic evaluation mechanism with a precision from low to high. The classification and assessment methodology of carbon dioxide geological storage in saline aquifers proposed could provide support (references) for potential of different regions and assessment stages, and also the management of deep underground space for saline aquifer carbon dioxide storage. However, the potential calculation formulas and key coefficient values are still need to be innovated through a large number of lab experiments, numerical simulation and project practices, as that are more consistent with the actual storage sites.