Evaluation of fault lateral sealing for CO₂ storage in offshore saline aquifers: a case study of Enping A Oilfield in Enping Sag, Pearl River Mouth Basin

Carbon capture, utilization, and storage (CCUS) has been considered a key strategy in addressing global climate change and holds strategic importance in achieving the "dual carbon" goals. Among various approaches, CO₂ storage in saline aquifers has been identified as the primary method of carbon sequestration. The sealing capacity of a fault seal is regarded as a crucial criterion for site selection in CO₂ geological storage, and the accurate evaluation of fault lateral sealing is considered critical for ensuring storage security. At present, most evaluation methods for lateral sealing focus on qualitative and quantitative assessments of conventional hydrocarbon reservoirs, while systematic methods and frameworks for CO₂ storage in saline aquifers remain limited. To address the key challenge of evaluating CO₂ storage security in offshore saline aquifers, the Enping A Oilfield in the Enping Sag of the Zhu Ⅲ Depression, Pearl River Mouth Basin, was selected as a case study. The heterogeneity of mineral distribution and cementation within key faults was investigated. Based on parameters including Shale Gouge Ratio (SGR), Across-Fault Pressure Difference (AFPD), and sealed gas column height, a method was developed for evaluating fault lateral sealing capacity for CO₂ storage, enabling assessments of sealing performance and identification of target layers for CO₂ storage. The results showed that the F1 and F3 faults possess static sealing capacity at the Yuehai 320 and Hanjiang 420 layers. The maximum CO₂ plume column heights are estimated to be 50 to 400 m and 175 to 300 m, respectively. Both formations exhibit favorable sealing and storage properties for CO₂ and can be consi-dered as target layers for CO₂ storage in the Enping A Oilfield. Based on the findings, a spatial sealing evaluation technique for faults was developed. By integrating fault throw-distance curves and single-well clay content data for different layers, fault surface attributes and fault sealing ternary diagrams were generated, enabling quantitative evaluation of fault zone sealing. The study provides a basis for the quantitative screening and assessment of saline aquifers for future CO₂ storage.