南海北部深水区盆地热历史及烃源岩热演化研究

南海北部深水区是中国重要的油气潜力区.本文在前人对其现今地温场和正演热史研究的基础上,利用磷灰石(U-Th)/He和镜质体反射率(Ro)数据对根据拉张盆地模型正演获得的热历史进行了进一步约束,并在此基础上对南海北部深水区的烃源岩热演化进行了研究.研究结果表明基于盆地构造演化模型的正演热历史可以作为烃源岩热演化计算的热史基础,而盆地内主力烃源岩热演化计算结果显示:南海北部深水区存在4个生烃中心,即珠江口盆地的白云凹陷和琼东南盆地的乐东凹陷、陵水凹陷和松南凹陷,生烃中心烃源岩有机质现今处于过成熟状态,以生气为主;受盆地基底热流显著升高的影响,32~23.3 Ma时段为南海北部深水区烃源岩快速成熟阶段,琼东南盆地烃源岩有机质现今(2.48 Ma后)还存在一期加速成熟过程,而珠江口盆地则不存在此期快速成熟过程.

Geothermal history and thermal evolution of the source rocks in the deep-water area of the northern South China Sea

The deep-water area of the northern South China Sea has a significant petroleum potential. Bases on the previous study of the present-day geothermal regime and the reconstructed thermal history from forward modeling, the rift basin model was further constrained by recently obtained vitrinite reflectance and (U-Th)/He data. The results suggest that the thermal history obtained from the basin model is suitable to calculate the maturation of the source rocks and there are four hydrocarbon generation centers in the deep-water area, namely, the Baiyun sag in Pearl River Mouth Basin, Ledong sag, Lingshui Sag and Songnan sag in Qiongdongnan Basin. In the hydrocarbon generation centers, the source rocks are of over-maturation and the gas is the major hydrocarbon production. Because of the effect of the heat flow from the basin basement, the source rocks maturated rapidly from 32 Ma to 23.3 Ma in the whole study area. The other rapid maturation processes occurred in present-day (after 2.48 Ma) in Qiongdongnan Basin but not in Pearl River Mouth Basin.