吐哈盆地台北凹陷侏罗系煤源岩排烃模拟研究

MODELING STUDY ON HYDROCARBON EXPULSION FROM JURASSIC COAL SOURCE ROCKS IN TAIBEI SAG OF TURPAN-HAMI BASIN

应用排烃门限控油气理论 ,对吐哈盆地台北凹陷侏罗系煤源岩排烃过程进行了数值模拟。模拟结果表明 ,研究区煤源岩在埋深 5 0 0m左右同时进入排甲烷气、排重烃气门限 ,并于 2 0 0 0m左右进入排液态烃门限。在埋深为 35 0 0m左右达到排烃高峰。现今 1m3 源岩排出的甲烷气、重烃气和液态烃量分别为 6 4.72m 3、3.82m 3和 34 .97kg。煤源岩主要以水溶、扩散、油溶和游离四种相态排运油气 ,其中油溶相和游离相起决定作用。甲烷气、重烃气和液态烃的排出效率分别为 73.5 %、6 6 .1%和 6 9.9%。排烃过程可划分为三个阶段 :水溶—扩散相初始排气阶段、早期游离相大量排气阶段和中期游离相大量排液态烃阶段 ,为三阶段多相态排油气地质模式。

The theory of hydrocarbon expulsion threshold was applied in a numerical simulation of hydrocarbon expulsion from lower-Jurassic coal source rocks in Taibei Sag, Turpan-Hami Basin. The results show that methane and heavier hydrocarbon gases were expulsed first at burial depth of about 500m. This was followed by expulsion of liquid hydrocarbons at burial depth of about 2000m. The rate of hydrocarbon expulsion reached a maximum at burial depth of around 3500m. Currently, the amount of methane, heavier hydrocarbon gases and oil expelled from 1 m3 coal source rocks is 64.72 m3, 3.82 m3 and 34.97kg, respectively. Main mechanisms of hydrocarbon expulsion from the coal source rocks include dissolution in formation water, diffusion, dissolution in oil and free phase, with the last two being the most important. Expulsion efficiencies for methane, heavier hydrocarbon gases and liquid hydrocarbons are 73.5%, 66.1% and 69.9%, respectively. The process of hydrocarbon expulsion can be divided into three stages: (I) gas expulsion by dissolution in formation water and by diffusion; (II) gas expulsion in free phase, and (III) oil and gas expulsion in free phase.