咸化湖盆优质烃源岩的形成与分布

Deposition and distribution of high-potential source rocks in saline lacustrine environments

应用沉积学、地球化学理论和油源对比等方法,对我国咸化湖盆优质烃源岩的形成与分布进行了研究。结果表明,断陷湖盆和前陆湖盆优质烃源岩(有机质含量特别高的烃源岩)是与碳酸盐、硫酸盐和氯化盐等蒸发盐类矿物相伴生的,有机质沉积的有利环境是半咸水、咸水和盐水湖泊。湖水在重力作用下易形成盐度分层,表层水盐度小,适于广盐和嗜盐性浮游生物的生存;深水部位的底层水盐度大、缺乏游离氧,适于有机质的保存;表层水生物高产率区与底层水缺氧区的叠合部位就是优质烃源岩的发育区。由气候变化引起的突发性洪水会破坏分层水体,使得湖水淡化,形成有机质含量较低的烃源岩,因此咸化优质烃源岩与淡化普通烃源岩常呈互层分布,咸化沉积物数量越多,生烃潜力越大。

Investigations of sedimentology and geochemistry as well as oil-source correlation show that major source rocks in non-marine basins are deposited in saline lakes and interbedded with carbonates, sulfates or chlorates. The source rocks are rich in organic matter, and often called high-potential source rocks. In other words, the high-potential source rocks are deposited in semi-saline, Saline or super-saline lacustrines. In these saline lacustrines, Water column is stratified by gravity for salinities. The surface water is in fresh or semi-saline, and suitable for living of euryhalinous organism. The bottom water at deep part of the lake is in super-saline and anoxic status, and is the best condition for preservation of deposited organic matter. If an area in the lake meets both high productivity of organism in the surface water and anoxic condition in the bottom water, the area is an ideal for accumulation of the high-potential source rocks. When the high-potential source rocks are buried into oil-generation window, they become into real hydrocarbon kitchens and control on distribution of oil and gas in the basins.