济阳坳陷渤南洼陷湖相碳酸盐岩成烃特征

Hydrocarbon-generation characteristics for lacustrine carbonate source rocks in Bonan Sag of Jiyang Depression

在济阳坳陷渤南洼陷沙河街组下部发育了一类以泥质灰岩、泥灰岩和泥质白云岩为主的富含有机质的湖相碳酸盐岩。其有机显微组分以矿物沥青基质和沥青质体为主;可溶有机质中饱和烃/芳烃值低,非烃和沥青质含量高;分子标志物的原始生物骨架结构保存好,重排类化合物含量低,有机含硫化合物丰富,并发育诸多特殊类型的标志物。湖相碳酸盐岩所表现出的这些特征与其特殊的沉积环境密切相关,硫酸盐还原菌、绿硫菌、蓝细菌等微生物是该类烃源岩形成的重要物质基础。综合考虑沉积相差异和成熟度的影响,可将二苯并噻吩与菲的比值大于1、重排甾烷及C30重排藿烷极不发育、富含2-甲基藿烷和30-降藿烷系列等条件作为判识湖相碳酸盐岩生油的标志。渤南洼陷湖相碳酸盐岩至少出现过两期生烃高峰,具备形成大规模商业性油藏的能力,可以成为我国陆相湖盆下一步优选的勘探目标。

Lacustrine carbonate source rocks composed of argillaceous limestones, argillaceous dolostones and marls with abundant organic matter were developed in the lower member of Shahejie Formation in Bonan Sag of Jiyang Depression. The macerals are mainly composed of mineral-bituminous matrix and bituminite. The extract has low saturate-to-aromatics ratio and high contents of resin and asphaltene. The carbon skeletons of liquid with several special molecular fossils are well preserved. The organic sulfur compounds with low rearranged compounds are abundant. These characteristics of molecular markers are concerned with the depositional environments. The microbes such as sulfate-reducing bacteria, green sulphur bacteria, and cyanobacteria are the primary bases for generating lacustrine carbonate source rocks. It is suggested that DBT/P value more than one, C36/C34 hopanes value more than one, poor rearranged compounds and rich 30-norhopanes may be the typical markers for judging hydrocarbon generation from carbon- ate source rocks. The result of oil-source correlation showed that carbonate source rocks had two peaks of hydrocarbon generation and could form large-scale commercial reservoirs. Therefore, it is an important target for oil exploration in Jiyang Depression.