The study on the source of the oil seeps and bitumens in the Tianjingshan structure of the northern Longmen Mountain structure of Sichuan Basin, China
The study on the source of the oil seeps and bitumens in the Tianjingshan structure of the northern Longmen Mountain structure of Sichuan Basin, China
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DOI：
10.1016/j.marpetgeo.2012.05.011
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发表时间：
2012-11
影响因子：
4.2
通讯作者：
Liang Wu;Y. Liao;Yunxin Fang;Ansong Geng
中科院分区：
文献类型：
--
作者：
Liang Wu;Y. Liao;Yunxin Fang;Ansong Geng
龙门山北部的天景山构造位于四川省北部，中国。该区存在两种主要的生油岩，即过成熟的印支-下寒武统生油岩和成熟的上二叠统生油岩。中、古生界海相地层中广泛存在石油渗漏和固体沥青，具有良好的勘探前景。然而，由于下寒武统烃源岩成熟度高，渗漏和沥青生物降解严重，天景山构造油源对比困难。将天景山构造二叠系栖霞组的一条渗漏油和两条寒武系严重退化沥青与其潜在的生油岩进行对比。利用加氢热解释放与下寒武统过成熟烃源岩的干酪根结合的生物标志物。所释放的生物标志物与抗热降解和生物降解的指标一起用于油源对比。根据地球化学资料和该区的石油地质背景，可以推断寒武系、奥陶系和志留系具有轻质同位素值的沥青(通常为δ13C和−34.0‰)来源于印支-下寒武统源岩，而二叠系储集层中的石油最初由印支-下寒武统源岩的石油充注，后来又由上二叠统源岩的石油充注。天景山构造的主要油源是印支-下寒武统烃源岩。上二叠统的烃源岩对邻近地层的储集层只有部分贡献。
The Tianjingshan structure of the northern Longmen Mountain is located in the north of the Sichuan province, China. Two primary source rocks are present in this region, the overmature Infracambrian-Lower Cambrian source rocks and the mature Upper-Permian source rocks. Oil seeps and solid bitumens occur extensively in the Mesozoic and Paleozoic marine strata, indicating good exploration prospects in this area. However, oil-to-source correlation in the Tianjingshan structure is difficult due to both high maturity of the Lower Cambrian source rocks and severe biodegradation of oil seeps and bitumens. In this work, one oil seep from the Permian Qixia Formation and two severely degraded bitumens from the Cambrian strata in the Tianjingshan structure were correlated with their potential source rocks. Hydropyrolysis was used to release biomarkers bound to kerogen of the overmature Lower Cambrian source rock. The released biomarkers were used for the oil-to-source correlation together with those indexes resistant to thermal degradation and biodegradation. Based on the geochemical data and the petroleum geological settings of the area, it can be inferred that the Cambrian, Ordovician and Silurian bitumens with light bulk isotopic values (commonly δ13C < −34.0‰) were sourced from the Infracambrian -Lower Cambrian source rocks, while the oil in the Permian reservoir was initially charged by the oil from the Infracambrian-Lower Cambrian source rocks and then later charged by the oil from the Upper-Permian source rocks. The Infracambrian-Lower Cambrian source rocks are the major oil source in the Tianjingshan structure. The Upper-Permian source rocks only partly contributed to the reservoirs in the neighbouring strata.