四川盆地东南缘习水吼滩志留系古油藏特征

Characteristics of Silurian destroyed oil reservoir in Houtan section of Xishui area in southeastern margin of Sichuan Basin

从烃源岩、储层、盖层等基本地质条件,沥青的地球化学特征,以及地层后期抬升的低温年代学等方面系统解剖了四川盆地东南缘习水吼滩志留系古油藏的成藏特征。习水吼滩古油藏的主要储层是下志留统石牛栏组亮晶生屑灰岩,储层沥青主要分布在生物碎屑颗粒之间和粒内溶孔中,该储层沥青来自志留系自身的烃源岩。志留系源岩生成于还原沉积环境中,有机质主要来自于低等水生生物。志留系储层中与油气包裹体共生的盐水包裹体均一温度平均为97.2℃,结合研究区地层沉积埋藏史,可以确定油气充注的时间大约为距今200Ma。邻近志留系古油藏的下奥陶统湄潭组粉砂岩样品的磷灰石裂变径迹表明,研究区在距今29Ma左右隆升到退火带之内,距今4.5Ma之后经受了加速隆升,约有2100～2450m厚的地层受到剥蚀,最终造成了古油藏的破坏。

The forming characteristics of the Silurian destroyed reservoir in the Houtan section in the southeastern margin of Sichuan Basin were studied according to the basic geologic conditions of source rocks, reservoir rocks and cap rocks,as well as the geochemistry characteristics of bitumen and the thermochronology of detritus minerals. The main reservoir rock of the destroyed oil reservoir is sparite with hioclastic. The bitumen distributed in the inter grain pores of biological detritus and their solution inner-grain pores. The content and distribution of isoprenoid, steranes and terpanes from bitumen in Silurian illustrated that the source rocks were deposited in the reduced environment, and the organic source mainly came from the low-grade hydrobiosm. The stable carbon isotope showed that the bitumen came from source rock of the Silurian. The mean homogenization temperature of saline inclusions coexisting with hydrocarbon inclusions is 97.2℃. Combined with the burial history of the studied area, the hydrocarbon infilling time was de termined to be about 200 Ma before present. The fission track age of apatite in the Ordovician Meitan Formation near the destroyed oil reservoir showed that the formation uplifted in anneal zone at about 29 Ma before present and accelerated uplifted at 4.5 Ma before present. The denudation thickness was about 2HI0 2450 m in the studied area, which finally destroyed oil reservoir.