珠江口盆地文昌A凹陷深层珠海组不同构造单元油气充注期次及差异性分析

Hydrocarbon Charging Stages and Their Differences in Different Structural Units of the Deep Zhuhai Formation in Wenchang A Sag, Pearl River Mouth Basin

珠江口盆地文昌A凹陷深部的古近系珠海组油气资源丰富,但不同区带油气成藏分布复杂,油气成藏时期的关键证据——包裹体的研究相对薄弱.为了准确厘定文昌A凹陷珠海组烃类充注时期,以研究区珠海组砂岩储层中的烃包裹体及其伴生盐水包裹体为研究对象,利用荧光光谱测定、激光拉曼光谱分析、显微测温等实验测试,结合包裹体捕获压力计算、埋藏史、热演化史、生烃演化史等分析,开展了凹陷中心及近珠三南断裂带油气成藏期次与差异性研究.结果表明,储层砂岩中烃包裹体及其伴生盐水包裹体成分主要为CH_(4)、C_(2)H_(6)、CO_(2)和H2O,同期盐水包裹体均一温度集中分布于95~180℃.断裂带与凹陷中心均存在3期烃类充注,但油气充注时间有差别.其中,凹陷中心第1期发生在21.9~13.9 Ma,第2期油充注发生在12.0~8.9 Ma,第3期油气充注时间7.8~4.8 Ma;断裂带第1期油充注发生在约21.7~10.2 Ma,第2期油充注发生在约9.1~4.9 Ma,第3期油气充注时间约为3.9~1.5 Ma.差异性构造沉降导致的烃源岩埋深的差异,以及多期断裂活动强度及其时空配置关系的不同,是造成凹陷中心及断裂带烃源岩生烃高峰的差异及油气成藏时间有先后之分的主要原因.该结果为研究区油气勘探目标的选取与部署提供科学依据.

The Paleogene Zhuhai Formation in the deep Wenchang A Sag of the Pearl River Mouth Basin is rich in oil and gas resources, but the distribution of oil and gas reservoirs in different regions is complex, and the study of inclusions, the key evidence of oil and gas accumulation period, is relatively weak. In order to accurately determine the hydrocarbon charging periods of Zhuhai Formation in Wenchang A Sag, the hydrocarbon inclusions and their associated brine inclusions in the sandstone reservoirs of Zhuhai Formation in the study area were taken as the research object. Fluorescence spectroscopy, laser Raman spectroscopy, micro thermometry and other related experiment were used, combined with the analysis of inclusion capture pressure calculation, burial history, paleogeothermal evolution history, and thermal evolution history of hydrocarbon source rocks.The research on hydrocarbon charging stages and their differences in the central depression and the fault zone has been carried out.The results show that there are three kinds of inclusions, including high-density single-phase oil inclusions, two-phase of gas-liquid hydrocarbon inclusions and two-phase of gas-liquid saline inclusions in the sandstonereservoir. The components of hydrocarbon inclusions and the associated brine inclusions are mainly CH_(4), C_(2)H_(6), SO_(2), CO_(2) and H2O, and the homogenization temperature of brine inclusions distributed mainly from 95 to 180 ℃. Three stages of hydrocarbon filling occurred both in the central depression and the fault zone, but the hydrocarbon filling time is different. The first hydrocarbon charging occurred in the central depression rangesfrom 21.9 to 13.9 Ma, the second oil filling occurred at 12.0 to 8.9 Ma, and the third oil and gas filling occurred at 7.8 to 4.8Ma. However, in the fault zone, the first oil charging occurred at 21.7 to 10.2 Ma, the second one occurred at 9.1 to 4.9 Ma, and the third oil and gas filling was about 3.9 to 1.5 Ma. The difference of source rock burial depth, multi-stage fault activity and their spatio-temporal configuration caused by different tectonic subsidence is the main reason for the difference of hydrocarbon generation peak and hydrocarbon accumulation time in the central depression and fault zone. The research results provide a scientific basis forselection and deployment of oil and gas exploration targets in the study area.