一个典型的寒武系油藏:塔里木盆地塔中62井油藏成因分析

塔里木盆地志留系沥青砂岩广泛发育,主要原因是来源于寒武系的原油在进入志留系储层后区域性的抬升剥蚀使油藏遭到严重破坏,但到目前为止,究竟是寒武系烃源岩还是中上奥陶统烃源岩或是两者都对现今的志留系沥青砂岩中的有机质有贡献还不清楚.对塔中62井原油的化学组成和油源的分析表明,其甾萜类组成具有寒武系烃源岩的组成特征,反映该油藏原油主要来源于寒武系.另一方面,塔中62井砂岩透镜体被泥岩圈闭,油藏具有较好的保存条件,且后期中上奥陶统生成的烃类难以充注进入油藏.塔中62井志留系油藏破坏作用较弱、保存较好,是塔里木盆地在志留系发现的第一例来源于寒武系的油藏.

A typical Cambrian oil reservoir: Origin of oil reservoir in Well TZ62, Tarim Basin

The distribution of the Silurian asphaltic sandstones is very widespread in Tarim Basin. After the oil derived from Cambrian entered into the Silurian reservoir, the regional uplift of the crust destroyed the oil reservoir. It is not sure whether the Cambrian source rocks or the Middle and Upper Ordovician ones or both of them made contributions to the organic matters in the Silurian asphaltic sandstones. The chemical compositions of oil and oil-source rock analysis from Well TZ62 show that its sterane and terpane compounds possess the characteristics of Cambrian source rocks, indicating the oil from Well TZ62 was derived mainly from Cambrian. On the other hand, the sandstone lens in Well TZ62 was well trapped by the Silurian mudstone; therefore the oil reservoir in Well TZ62 has a good preservation condition, and was difficult to be filled by the later formed Middle and Upper Ordovician hydrocarbons. Accordingly, the Silurian oil reservoir in Well TZ62 is an ancient reservoir that was degraded slighter and preserved better than others. Among the reservoirs discovered in Tarim Basin, the oil reservoir in Well TZ62 is the first integrally preserved Silurian oil reservoir.