孤南洼陷低熟油成因分析

济阳坳陷孤南洼陷低熟油的地质储量可达数千万吨，类似的由沙一段和沙四段烃源岩形成的低熟油在渤海湾盆地普遍可见。以孤南洼陷为例，讨论了低熟油勘探中的有关问题。明确提出判别低熟原油的指标是其Ｃ２９甾烷的异构化系数（其值０．３０～０．３５可作为上限值），ＯＥＰ及Ｐｒ／ｎＣ１７和Ｐｒ／ｎＣ１８可作为辅助指标。低熟原油可以是中等密度的高蜡油，其组分特征是高饱芳比和高非沥比。孤南洼陷生成低熟油的沙一段烃源岩为富含藻类有机质的油页岩，形成于半咸水—咸水、强还原的沉积环境。孤南洼陷低熟油形成阶段的Ｒｏ值上限为０．４０％～０．４５％，相应的深度为２３００～２５００ｍ；Ｒｏ值下限为０．６０％～０．６５％，相应的深度为３０００～３２００ｍ。咸水环境由富含藻类的有机质早期生烃，可能是最主要的低熟油形成机制。图２表４参８（邓春萍摘）

The genesis of low-mature oil in the Gunan sag .

This paper discusses the practical problem in the exploration of the low mature crude oil , taking the Gunan sag in the Shengli petroleum province as an example . It proposes clearly that the criterion of the low mature crude oil is the isomerization index of C 29 steranes and 0.30 0.35 can be taken as the upper limits . The values of OEP and Pr/nC 17 , Ph/nC 18 also provide the supplementary indicators . This kind of oil has medium density and high wax content . The chemical composition is characteristic of high ratios of saturated HC to aromatic HC and non HC to asphaltene . The source rock in the First Menber of the Shahejie Formation of the Oligocene in the depression is the oil shale which is rich in the organic matter and was deposited in the semisaline saline environment . The generating onset of the low mature crudeoil in the Gunan depression corresponds to R o 0.40 % 0.45 % and 2,300 2,500 m, while upper limit to R o 0.60 % 0.65 % and 3,000 3,200m. The geological resources of the low mature crude oil in the Gunan depression attains hundreds thousands tons , and similar oils from the First Member and Fourth Member widespread in all over the Bohai Bay basin . Therefore , the generation of the low mature oil from algal organism deposited in the saline environment may be the most important .