CO2 geological storage in sedimentary basins: An update on the potential and suitability evaluation and a field test

Abstract

China has pledged to peak carbon dioxide (CO₂) emissions by 2030 and achieve carbon neutrality by 2060. Carbon capture and storage (CCS) will play a key role in these efforts. Over the past several years, the China Geological Survey (CGS) has completed the Suitability Evaluation Map of CO₂ Geological Storage in Main Sedimentary Basins in China and Adjacent Sea Regions in 2017. This map reflects the suitability of the first- and secondary-order tectonic units within sedimentary basins for CO₂ geological storage for CCS planning. The Junggar Basin is recognized as an important region for future CCS projects. Results from a mesoscale evaluation using the volume method indicate that deep saline aquifers represent the most significant resources for CO₂ storage, with potential ranging from 48 × 10⁹ to 164 × 10⁹ t (with a P50 value of 96 × 10⁹ t). The highest storage potential is identified in the central and northern parts of the basin, reaching up to 9.5 × 10⁶ t/km² at the P50 probability level. In contrast, the hinterland, eastern, and western parts of the basin generally exhibit storage potential of below 1.0 × 10⁶ t/km² at the same probability level. The CGS has also characterized historical CO₂ plume migration in reservoirs at the storage site of the Shenhua CCS demonstration project and conducted numerical simulations of CO₂ plume migration for periods of 10 and 20 years following the shutdown of the injection well. The CGS implemented a kiloton-scale pilot test on CO₂-enhanced water recovery (CO₂-EWR) in eastern Junggar, revealing that CO₂ flooding can improve the pressure for fluid production, with the highest ratio of CO₂ to produced fluids estimated at approximately 1.2. Besides, an observation field for natural CO₂ leakage, covering about 930 m², was built in Qinghai Province. In natural CO₂ fields or at artificial CO₂ injection research sites, CO₂ leakage points are primarily related to the distribution of faults (especially fault crossing), which can serve as pathways for CO₂ leakage. The observation field provides a natural analog to wellbore failure and offers an opportunity to further monitor CO₂ geological storage sites. However, it has been inferred that borehole ZK10 at the observation field has become a leakage pathway due to the drilling activities, inadequate well-plugging, and abandonment procedures without considering CO₂ corrosion.