低势控藏特征与动力学机制及在油气勘探中的作用

含油气盆地油气藏的形成和分布受低势场控制.济阳坳陷已发现的油气藏分布特征表明: 在势场作用下, 油气只能进入到孔隙度超过某一临界值或内部势能低于周边势能2倍到100倍以上的储层内聚集成藏; 随着埋深加大和储层孔隙度变小, 圈闭聚集油气成藏的临界条件呈规律性变化, 即埋深较大的圈闭成藏时要求的相对势能较浅部储层的势差更大.动力学分析和物理模拟实验研究表明, 地表条件下储层聚集油气的前提条件是其孔喉半径大于周边围岩的两倍以上; 地下储层聚集油气的前提是它与周围介质间的毛细管力之差大于储层内部的毛细管力与上覆静水柱压力之和.圈闭内外势差越大, 它们聚集油气的饱和度越大, 聚集的油气量越多.低势控藏特征与动力学机制分析表明: 对深层来说, 只要储层的物性比周边围岩的物性好到一定程度就能成藏, 即便本身低孔低渗也能有油气聚集.通俗的说, 油气成藏没有死亡线(不考虑油藏经济价值), 这就极大地扩充了含油气盆地油气勘探的领域和深度; 对浅层来说, 高孔渗砂体周边的相对低孔渗砂体能作为有效盖层, 不一定需要有巨厚泥岩充当盖层, 这一观点的提出可以在一定程度上扩大浅层油气勘探的领域和有利区. 

Characteristic and Dynamics Mechanism of Low Potential Controlling on Hydrocarbon Accumulation

The formation and distribution of hydrocarbon accumulation are controlled by the fluid potential in oil-bearing basin. The distribution characteristics of discovered hydrocarbon accumulation in the Jiyang superdepression show that hydrocarbon could only be accumulated in the reservoir rock where the potential varies from 2 to 100 times of the potential of the surrounding rock. A certain critical value of porosity is necessary for hydrocarbon accumulation in depth. The research also suggests that the porosity decreases and the critical formation condition of hydrocarbon accumulation changes with the burial depth. The trap in the deep burial depth should meet the condition of relatively lower potential compared with the trap in the shallow burial depth. The dynamic analysis and physical experiments also show that the premise condition of hydrocarbon accumulation in the surface of the earth is pore radii in the reservoir rock is double of that in the surrounding rock. The premise condition of hydrocarbon accumulation in the underground reservoir rock is the capillary pressure disparity higher than the sum of capillary pressure and the stratigraphic pressure in the reservoir., which suggests that the lower potential in the trap would cause the higher oil saturation and resources in the reservoir. The characteristics and dynamic analysis suggest that hydrocarbon can be accumulated in the deeper reservoir with low porosity and permeability only if the physical property of reservoir is better than that of the surrounding mudstone, which could extend the hydrocarbon exploration domain and depth. The characteristics also suggest that sand with relative low porosity and permeability can be cap rocks for sand with relatively high porosity and permeability, which could broaden the favorable exploration area in the shallow strata.