四川宣汉盘龙洞晚二叠世生物礁古油藏剖面序列

The Late Permian organic reefal oil pool section in Panlongdong, Xuanhan, Sichuan

盘龙洞生物礁发育于上二叠统长兴组的中上部,厚度约80m。生物礁主要为浅灰色块状海绵障积岩、海绵骨架岩。造礁生物主要为房室海绵、水螅、苔藓虫等;附礁生物主要为腕足、瓣鳃及腹足等;造架生物含量约为30%～50%;充填物为泥晶方解石,含量为50%～70%;孔洞丰富,多被方解石晶体充填,孔洞间连通性好。该生物礁及其上下地层均有大量的沥青,揭示着有过油气的运移过程。沥青充填可以分为两期:第一期充填于生物骨架孔隙、粒间孔隙、海绵体腔和部分其他生物体腔孔隙中;第二期主要充填于后期裂隙和次生孔隙中,该期的沥青广泛分布于生物礁和整个礁的盖层之中(包括亮晶砂屑灰岩和白云岩),规模较大,含沥青的地层总厚度达120m左右。

The Panlongdong organic reefs are developed in the middle and upper parts of the Upper Permian Changxing Formation, with a thickness of about 80 m. The organic reefs consist dominantly of light gray massive spongy bafflestone and spongy skeletal limestone. The reef-building organisms are composed of room-type sponges, polys, bryozoans and so on. The reef-attached organisms comprise brachiopods, pelecypods and gastropods. The frame-builders make up about 30 to 50%. The fillings are made up of micritic calcite, with a content of 50 to 70%. Abundant pore spaces are well connected, and almostly filled by calcite crystals. The occurrence of abundant asphalt in the organic reefs and the strata above and below them has disclosed the migration of oil and gas. Two phases may be identified for the filling processes of the asphalt: the one is the filling into organic frameworks, intergranular pores, sponges and other organic coelomata such as brachiopods; the other is the filling into paulopost fissures and secondary pores. In this phase, the asphalt is widespread in the organic reefs and their cap rocks (including spararenite and dolostone). The asphalt occurs on a large scale in this phase, and the asphalt-containing strata amount to about 120 m in total thickness.