CO₂地质封存被认为是实现碳中和目标的兜底技术，近海沉积盆地远离人类活动区，在实施CO₂地质封存方面相比于陆上沉积盆地更具优势。为查明广东省近海北部湾盆地涠西南凹陷咸水层CO₂封存潜力，基于盖层埋深、单层泥岩最大厚度、泥地比、断层密度和储层孔隙度、地层厚度、砂地比、渗透率等8个指标，构建了盆地二级构造单元的储盖评价体系，结合各地层岩心物性资料和三维地质模型，对涠西南凹陷储盖进行优选，并以US-DOE法对有效封存潜力进行了评估。研究结果表明，涠西南凹陷在海底以下800～3 000 m内，有2套适宜CO₂封存的储盖组合。储盖组合1：新近系角尾组一段浅海相泥岩盖层−角尾组二段、下洋组滨浅海相砂岩储层，有效封存容量为7.49亿t；储盖组合2：古近系涠洲组二段中深湖泥岩盖层−涠洲组三段砂岩储层，有效封存容量为3.74亿t。在涠西南凹陷中优选出2套适宜咸水层封存CO₂的储盖组合，有效封存容量为11.23亿t，按照广东省粤西地区CO₂年排放量为7 000万t进行评估，能够满足该地区超16 a的CO₂减排需求。

CO₂ geological storage is a guaranteed technology for achieving carbon neutrality. The offshore deposit basin is far away from the human activity area, and the implementation of a CO₂ geological storage is more advantageous than the land sedimentary basin. To find out the CO₂ storage potential in the Weixinan sag of the Beibu Gulf Basin, based on the 8 indicators such as caprock burial depth, the maximum thickness of single layer mudstone, mud-soil ratio, fault density and reservoir porosity, formation thickness, sand-soil ratio, permeability, etc., it has established a reservoir evaluation system for the secondary structure unit of the basin. Combined with the core physical property data of lays and 3D geological models, the reservoir and caprock of the Weixinan sag are optimized, and the effective storage potential is evaluated with the US-DOE method. The results show that within 800−3000 meters below the sea floor, in the Weixinan sag, there are two sets of reservoir-cap combinations suitable for CO₂ storage. Combination 1: in Neogene, the neritic mudstone of the first member of the Jiaowei Formation is the cap rock, and the neritic sandstone of the second member of the Jiaowei Formation and the Xiayang Formation is the reservoir, and the effective storage capacity is 0.749 billion tons. Combination 2: in the Paleogene, the deep lake mudstone in the second member of the Weizhou Formation is the cap rock, and the sandstone in the third member of the Weizhou Formation is the reservoir, and the effective storage capacity is 0.374 billion tons. In the Weixinan sag, two sets of reservoir-cap assemblages suitable for CO₂ storage in the saline aquifers are selected, with an effective storage capacity of 1.123 billion tons. According to the evaluation of the annual CO₂ emission of 70 million tons in the west of Guangdong Province, it can meet the CO₂ emission reduction needs of the region for more than 16 years. Offshore geological storage is a potential path for the green and sustainable development of coastal heavy chemical clustering areas and to achieve the goal of carbon neutrality.