The found gas pools in the Songdong and Baodao regions in the eastern Qiongdongnan basin, South China Sea have almost failed to realize expected commercial value due to either low reserve abundance or high carbon dioxide (CO₂) content. To assist in further exploration, the genetic type, source and accumulation history of natural gas have been investigated based on the analysis of the chemical compositions, carbon isotopes and light hydrocarbons in gases, isotope compositions of rare gas, basin numerical modeling and fluid inclusion analysis. The results indicate that there are three representative types of gases. The first type distributed in the BD13 and ST24-1 areas consists of biogenic and oil-derived gases from the Songdong sag. The second type distributed in the BD19-2 area is composed of coal-derived and oil-derived gases from the Baodao sag. The third type distributed in the BD15-3, BD19-4 and BD19-2 areas consists of significant amounts of volcanic mantle-derived CO₂ and few organic hydrocarbon gases. The charge of oil-derived gas and formation of biogenic gas are close to the deposition stage of overlying thick mudstones. This may be a critical factor for current gas pools with low reserve abundance in the Songdong region. Intense activity of the No.2 fault and absence of overlying thick mudstones gave rise to the escape of a large quantity of oil and gas from the middle Oligocene to middle Miocene. Besides, due to volcanic activity in the Quaternary, mantle-derived CO₂ was injected into the reservoirs via No.2 fault. The previous accumulative hydrocarbon gases were driven off by CO₂ in various degrees, which may be mainly responsible for current situation that most gas pools have high CO₂ content in the Baodao region.

南海琼东南盆地东部的松东和宝岛地区发现的气藏由于储量低或二氧化碳（CO _2）高而几乎无法实现预期的商业价值。） 内容。为了帮助进一步探索，在分析化学成分，气体中的碳同位素和轻烃，稀有气体的同位素组成，盆地数值模拟和流体包裹体分析的基础上，研究了天然气的遗传类型，来源和积累历史。 。结果表明存在三种代表性的气体类型。分布在BD13和ST24-1地区的第一类气体由松东凹陷的生物气和石油衍生气组成。分布在BD19-2地区的第二种类型是由宝岛凹陷的煤和石油衍生的气体组成。分布在BD15-3，BD19-4和BD19-2地区的第三种类型由大量火山地幔衍生的CO _2组成几乎没有有机碳氢化合物气体。石油来源的气体和生物气的形成接近上覆厚泥岩的沉积阶段。对于松东地区目前储量低的气藏来说，这可能是一个关键因素。2号断层的强烈活动和上覆的厚泥岩的缺失导致大量的油气从中渐新世到中新世。此外，由于第四纪的火山活动，地幔衍生的CO ₂通过2号断层注入到储层中。以前的累积烃气被不同程度的CO ₂驱除，这可能是造成目前宝岛地区大多数气藏CO ₂含量较高的现状的主要原因。