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南海北部各盆地普遍存在含CO_2气藏。莺歌海盆地CO_2主要受泥底辟带热流体上侵作用的控制,异常高CO_2仅在泥底辟带发现。然而珠江口盆地白云凹陷的泥底辟带与CO_2的关系暂不明确。通过收集分析珠江口盆地的60组(含/高含)CO_2气藏的气体组分和气体同位素地球化学数据,其R/Ra比值(样品的3 He/4 He与空气的3 He/4 He比值)均>2,CO_2成因主要为火山幔源型,不同于以壳源型为主的莺歌海盆地。位于白云凹陷中央泥底辟带的B1井,其CO_2碳同位素δ13 C值约-10.9‰~-10.5‰,根据自生片钠铝石的出现认为曾有CO_2大量聚集,而且CO_2分压高,推测为有机、无机成因混合气,不同于非泥底辟带的幔源无机成因。通过不同构造位置上的3口典型单井的对比分析及其与莺歌海盆地,以及泥底辟带和非泥底辟带的对比研究,认为凹陷周缘凸起上的断裂带和凹陷内的泥底辟带是高含CO_2气藏的主要分布区,认为白云凹陷泥底辟构造对于CO_2分布具有一定的控制作用。
CO 2 gas reservoirs are commonly found in all the basins in the northern South China Sea. The CO 2 in the Yinggehai Basin is mainly controlled by the thermal intrusion of the mud zone diapir. The abnormally high CO 2 level is only found in the mud zone. However, the relationship between the mud zone and CO_2 in the Baiyun Depression of the Pearl River Mouth Basin is not yet clear. By collecting and analyzing the gas composition and gas isotopic geochemical data of 60 groups of gas reservoirs in the Pearl River Mouth Basin, the R / Ra ratio (3 He / 4 He and 3 He / 4 He Ratio)> 2. The main cause of CO_2 is volcanic mantle-derived type, which is different from Yinggehai basin dominated by crust type. The B1 well located in the central mud belt in the Baiyun Sag has a δ13 C value of about -10.9 ‰ ~ -10.5 ‰ for carbon dioxide. According to the advent of spontaneous wadolite, it is thought that there was a large accumulation of CO 2 and the partial pressure of CO 2 is high For the organic, inorganic genetic mixture, different from the non-muddy zone of mantle-derived inorganic origin. Through the comparative analysis of three typical single wells in different tectonic positions and their correlation with the Yinggehai Basin and between the diabases and the non-mud belt, it is considered that the fractures and depressions in the protuberances The diapir zone is the main distribution area of high CO_2 gas reservoirs. It is considered that the diapir structure of Baiyun Sag has some control over the distribution of CO_2.