对油气运聚研究中一些概念的再思考

Reconsideration on some concepts in research of hydrocarbonmigration and accumulation

非均质地层中烃类的扩散流和达西流可以同时存在,并可相互转换。据 Welte等 1997年计算,在致密泥岩层中,扩散流和达西流的流速分别为18m/Ma和15m/Ma,说明在致密地层中这两种流动几乎没有差别,同时说明了泥岩中的流动也可以用达西公式来表述。油、气的浮力流和渗流虽然都是在地下多孔介质中的流动,但前者是油、气在水中上浮,不呈连续相流动,而后者是油、气呈连续相与水一起流动,因此浮力流没有含烃饱和度和相对渗透率的要求,也不能用达西公式表述,而渗流则要求有临界运移饱和度和相对渗透率,并可用达西公式来计算。是否发生浮力流只取决于油、气与水的密度差,浮力流是二次运移最基本的流动模式。地下确实存在油。气的幕式运移和幕式充注,但幕式是一个有时间尺度的概念。油、气的运移和聚集是一个带幕式特征的连续过程,不能只强调强度较大的幕式活动而忽视了连续过程的存在,再加上油源的不稳定和通道的非均质性,因此单依据流体包裹体的分析就确定油气藏是由2或3期充注所形成,似乎有些难以置信。图3参18（李明诚摘）

Diffusive transport and Darcy's flow of hydrocarbon may coexist and transform each other in the heterogeneous formation. Since the calculated rate of the diffusive transport and the Darcy's flow in the tight mudstone is about 18m/Ma and 15m/Ma respectively (from Welte, et al. 1997), there is little difference between these two kinds of flow in the dense mudstone, and Darcy's law is suitable for describing the flow in the mudstone as well. Although both the buoyant ascent and the seepage flow of oil and gas are flows through the subsurface porous media, the former, buoying on the water, moves in discontinuous phase and the latter moves together with water, in continuous phase. Hence, buoyant ascent does not need the requirements of critical migration saturation and relative permeability, and can't be described by Darcy's law, while the seepage flow requires critical migration saturation and relative permeability, and it can be described by Darcy's Law. Buoyant ascent, caused only by the difference between the densities of hydrocarbons and water, is the basic mode of the secondary migration. Episodic migration and episodic injection do take place under the ground, but the episode is one concept measured by time. The migration and accumulation of oil and gas is a continuous progress with episodic features. We can't only emphasize strong episodic activities and neglect the continuous progress. Moreover, considering the instability of oil sources and the heterogeneity of the pathways, it seems unbelievable that analysis of fluid inclusions is enough to assure that oil and gas pools formed during two or three injection stages.