珠江口盆地文昌A凹陷油气差异分布特征

DIFFERENCES IN OIL AND GAS DISTRIBUTION PATTERNS IN THE WENCHANG A SAG OF PEARL RIVER MOUTH BASIN

在烃源岩分布特征、有机质丰度、类型和成熟度分析的基础上,运用含油气盆地数值模拟技术,定量恢复了烃源岩热成熟演化史,探讨了油气差异分布特征。研究表明,文昌A凹陷各层系烃源岩分布广,厚度大,有机质丰度高;有机质类型文昌组偏Ⅱ1型,恩平组偏Ⅲ型,二者现今多处于高成熟—过成熟阶段。凹陷内烃源岩成熟时间早(文昌组约45.5Ma),现今成熟度高,以干气生成为主;凹陷边缘烃源岩成熟时间较晚(文昌组约30.0Ma),现今成熟度相对较低,以石油生成为主。凹陷现今油气差异分布的格局受制于有机质类型差异和热演化史不同,且下一步油气勘探方向,凹陷内以天然气为主,凹陷边缘以石油为主。

In order to better understand the process and mechanism of hydrocarbon accumulation, the source rocks in the Wenchang A Sag of the Pearl River Mouth Basin is studied in this paper. Basin modeling was carried out to reconstruct the thermal evolution history of the study area based on the distribution pattern of source rocks and the abundance, type and maturity of organic matters. Data show that each source rock in the Wenchang A Sag is widely distributed with high abundance of organic matter and large thickness. The organic matter of the Wenchang Formation belongs to type Ⅱ1, but the organic matter of the Enping Formation is type Ⅲ, and the source rocks are moderately or over matured. The source rocks entered into the oil threshold earlier in the inner part, but later in the outer part of the Sag, which remains in the low maturity today. The difference in oil and gas distribution pattern in the Wenchang A Sag is constrained by the differences in both the type and the maturity of organic matters. The inner part of the sag should be rich in gas, and the edge of the sag is the pros- pecting area for oil accumulation.