油气运移基础理论与油气勘探

在非均质地层中，烃类的扩散流和体积流可以同时存在并可相互转换．扩散流有助于烃类从源岩中排出，并通过流动方式的转变直接参与油气的聚集成藏．在致密泥岩层中，扩散流和体积流的计算流速分别为4～18m／Ma和3～15m／Ma，几乎没有差别，说明泥岩中的流动也可以用达西公式来表述．虽然油气的浮力流和渗流都是地下多孔介质中的流动，但油气在水中上浮不呈连续相流动．因此不要求也不能用达西公式表述临界运移饱和度和相对渗透率．优势运移通道和有效运移空间是2个不同的概念，前者是指油气运移的主要方向，后者是指地层中真正发生了油气运移的空间．大约有70％的油气藏位于优势运移通道上，而在运载层中有效运移通道空间约占总孔隙空间的5％～10％．圈闭的封盖强度与闭合度有3种不同的组合类型，它们是世界上油气分布的主控因素．根据研究和统计，世界石油储量的半衰期约为29Ma，大油田的中值年龄约为35Ma．根据烃类的微渗漏流量计算，中一大型油气藏的平均自然年龄约为50～100Ma．

Basic Principles of Migration and Hydrocarbon Exploration

Diffusive transport and volume flow of hydrocarbon may coexist and transform each other in the heterogeneous formation. Diffusive transport is helpful to hydrocarbon expulsion from source rock and directly contributes to oil and gas accumulation by transform of flow pattern. The calculated rates of the diffusive and volume flow in the tight mudstone, with the flow velocity of 4-18 m/Ma and 3-15 m/Ma respectively, show little difference, which indicates that Darcy's law is suitable for describing the flow behavior in the dense mudstone. Hydrocarbon migrates in the buoyancy-driven flow or the seepage flow through the subsurface porous media, but it moves upward in discontinuous phase in the course of buoyant ascent. Hence, the buoyant ascent does not relate with critical migration saturation and relative permeability, and can't obey the Darcy's law. Two concepts on hydrocarbon migration have been discussed, i.e. dominant migration pathway and effective migration space, the former implies main direction of hydrocarbon migration and the latter refers to the space in which the hydrocarbon migration really occurred. About 70% oil and gas reservoirs are situated in the dominant migration pathway, while the effective migration space occupies only about 5%-10% of total porous space in a carrier bed. There are three types of traps according to the different combinations of seal strength and trap closure, which are the key controlling factors on the distribution of oil and gas. On the basis of research and statistics, the half-life of petroleum reserve is inferred to be about 29 Ma, and the average age of a giant oil field is about 35 Ma. According to the calculated results of hydrocarbon microseepage fluxes, the average natural age of a median-giant oil and gas field is thought to be about 50-100 Ma.