古龙凹陷青山口组超压源岩天然气扩散速度演化史

为了研究古龙凹陷青山口组超压源岩天然气扩散速度演化史,在其内超压形成与演化研究的基础上,对其天然气向外扩散特征及其演化史进行了研究,得到在嫩四段沉积早期其内异常含气浓度开始形成,发生向上和向下的扩散作用。之后扩散作用逐渐增强,但在嫩四段沉积中后期和第四系沉积末期因异常含气浓度降为最低点,使天然气向外的扩散作用降为最弱。据此可把青山口组超压源岩向外扩散作用的过程划分为3个演化阶段,在每一演化阶段内天然气向上和向下的扩散速度均是逐渐增强的,但向下的天然气扩散速度大于其向上的天然气扩散速度,使扩散相天然气在下伏油层中的聚集较其在上覆油层中的聚集更有利,这可能是造成该区扶、杨油层天然气较萨、葡、高油层富集的一个重要原因。

Evolution History of Gas Diffusion Velocity from Overpressured Source Rock of Qingshankou Group (K1qn)in Gulong Sag

The evolution history of gas diffusion velocity from overpressured sourcerock of Qing-shankou Group(K1qn) in Gulong sag has been studied based on the study of formation and evolution of the overpressure.The result shows that abnormal gas-bearing concentration of K1qn was formed in the early of K1n2 sedimentation period,then the gas began to diffuse upward and downward.Because abnormal gas-bearing concentration decreased to the smallest value,the gas diffusion was the weakest in the middle and late K1n4 sedimentation period and in the end of Quaternary sedimentation period.Therefore the gas diffusion of overpressured sourcerock of K1qn is divided into three evolution stages.The gas diffusion velocity increases gradually upward and downward in each stage,but the gas diffusion velocity downward is bigger than that upward.It is more favorable for gas in diffusion phase to accumulate in oil layer under K1qn than that above K1qn.This is the reason that gas accumulates much more in the oil layer under K1qn than that above K1qn.