Recently, increasing numbers of oil and gas reservoirs have been discovered in the Wenchang Depression, western Pearl River Mouth Basin, South China Sea, revealing prospects for hydrocarbon exploration. The Enping Formation (E3e) is a key target layer for the development of source rocks. However, previous work has only focused on lacustrine swamp source rocks of E3e in the Wenchang A Sag, without a systematic study of shallow lacustrine source rocks. In this study, the quality of E3e shallow lacustrine source rocks is reevaluated, and the hydrocarbon generation and expulsion characteristics are analyzed using relevant geological data and constructing a conceptual model. The results show that the E3e2 source rocks have greater thickness (50–600 m) and similar organic matter abundance (0.5–2.5%) compared with the E3e1 source rocks (50–500 m and 0.5–2.5%). On the whole, the E3e source rocks were deposited in the continental environment and are dominated by Type II and Type III kerogen. Meanwhile, the E3e source rocks of the Wenchang A Sag are in the stage of mature to over mature, while those of the Wenchang B Sag are in the stage of low mature. Vertically, the hydrocarbon generation potential of the E3e2 source rocks is greater than E3e1. Also, the cumulative hydrocarbon production of steep slope in the Wenchang A Sag is larger than that in the Wenchang B Sag. In addition, the corresponding vitrinite reflectances of hydrocarbon expulsion threshold and peak are 0.72 and 0.96%, respectively. Horizontally, four hydrocarbon generation and expulsion centers were mainly concentrated in different subsags of the Wenchang A and B Sags for E3e. The maximum values of hydrocarbon generation and expulsion intensity for E3e1 are 1500 × 104 t/km2 and 1000 × 104 t/km2, respectively, while those for E3e2 are 1800 × 104 t/km2 and 1200 × 104 t/km2, respectively, with the expulsion efficiency of 75%.

中文翻译：

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南海珠江口盆地西部文昌坳陷始新世恩坪组烃源岩质量、生烃与排烃

近年来，在南海珠江口盆地西部文昌坳陷发现越来越多的油气藏，油气勘探前景广阔。恩平组（E3e）是烃源岩发育的关键目标层。然而，以往的工作仅集中于文昌A凹陷E3e湖相沼泽烃源岩，对浅层湖相烃源岩缺乏系统研究。本研究对E3e浅层湖相烃源岩质量进行重新评价，利用相关地质资料分析生排烃特征，构建概念模型。结果表明，与E3e1烃源岩（50-500 m和0.5%）相比，E3e2烃源岩具有更大的厚度（50-600 m）和相似的有机质丰度（0.5-2.5%）。5–2.5%）。总体上，E3e烃源岩沉积于陆相环境，以Ⅱ型和Ⅲ型干酪根为主。同时，文昌A凹陷E3e烃源岩处于成熟-过成熟阶段，文昌B凹陷E3e烃源岩处于低成熟阶段。纵向上，E3e2 烃源岩生烃潜力大于 E3e1。文昌A凹陷陡坡累计油气产量大于文昌B凹陷。此外，相应的排烃阈值和峰值的镜质体反射率分别为0.72%和0.96%。横向上，E3e 4 个生排烃中心主要集中在文昌A 凹陷和B 凹陷的不同凹陷。