The Xihu Sag in the East China Sea Shelf Basin contains abundant oil and gas reserves and is a focus for hydrocarbon exploration and development. Source rocks are mainly coals and coal-measures mudstones in the Paleogene Pinghu and Huagang formations. Samples from the Pinghu Formation in the Xihu Sag were collected for petrology, total organic carbon, and Rock-Eval analysis for the purpose of investigating macerals component and their contributions to hydrocarbon generation potential. The coaly source rocks from the Pinghu Formation are dominated by vitrinite (average 86.18%) but have an obviously elevated content of liptinite (average 12.59%) and a much lower amount of inertinite (average 1.23%). Liptinite of the samples is mainly composed of resinite, with a small amount of cutinite, sporinite and alginate in descending order. TOC values are 37.55%–65.58% (average 49.16%). Effective HI values are 167–281 mg HC/g TOC (average 223.5 mg HC/g TOC), suggesting the organic matter is type II kerogen. Relatively high HI values and macerals components suggest that the coaly source rocks can generate both oil and gas. Although the liptinite in the coaly source rocks has a content lower than vitrinite values, it makes a significant contribution to both total hydrocarbon and liquid hydrocarbon generation. The contributions of vitrinite, liptinite and inertinite to the total hydrocarbon generation approximately are 63.21%, 36.46% and 0.33%, respectively. The contributions of vitrinite and liptinite to the liquid hydrocarbon generation are approximately 40.95% and 59.05%, respectively. These results demonstrate that the coaly source rocks are dominated by vitrinite macerals with a relatively higher content of liptinite macerals, especially resinite, and these source rocks are more prone to both total hydrocarbon and liquid hydrocarbon generation. Paleogene coaly source rocks from other parts of the world should be considered for their oil-prone nature.

中文翻译：

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东海陆架盆地西湖凹陷平湖组煤质烃源岩岩石学及油气意义

东海陆架盆地西湖凹陷油气储量丰富，是油气勘探开发的重点。烃源岩主要为古近系平湖组和花港组煤和煤系泥岩。采集西湖凹陷平湖组样品进行岩石学、总有机碳和Rock-Eval分析，以研究微晶成分及其对生烃潜力的贡献。平湖组煤质烃源岩以镜质体为主（平均 86.18%），但锂铁质含量明显升高（平均 12.59%），惰性质含量低得多（平均 1.23%）。样品的脂质岩以树脂岩为主，依次含有少量角质岩、孢子岩和海藻酸盐。TOC 值为 37。55%–65.58%（平均 49.16%）。有效 HI 值为 167–281 mg HC/g TOC（平均 223.5 mg HC/g TOC），表明有机质为 II 型干酪根。相对较高的 HI 值和微量组分表明煤质烃源岩可以同时产生油气。尽管煤质烃源岩中的脂质岩含量低于镜质体值，但它对总烃和液态烃的生成都有显着贡献。镜质体、菱质体和惰性体对总生烃的贡献率分别约为 63.21%、36.46% 和 0.33%。镜质体和脂质体对液态烃生成的贡献分别约为 40.95% 和 59.05%。这些结果表明，煤质烃源岩以镜质体为主，脂质体含量相对较高，尤其是树脂岩，这些烃源岩更容易产生总烃和液态烃。应考虑来自世界其他地区的古近系煤质烃源岩的油性。