毛细管突破压力模拟实验及页岩封闭能力

为了研究流体流动路径上的多个两相流体界面对岩石封闭能力的影响，利用单个毛细管进行了不同条件下的突破压力模拟实验。结果显示，毛细管中为单相流体时，使流体流动所需的突破压力与毛细管的直径有关而与毛细管长度无关；当毛细管中的流体为气液混合相时，所需突破压力随气水界面数的增加而增大；而毛细管的表面润湿性的变化则会使得突破压力随气水界面数目而变化的趋势更加显著。根据实验结果认为，富有机质页岩作为盖层时，生成的烃类流体与岩石中的水形成了混合相流体，而疏水的有机质表面和亲水的矿物表面形成润湿性不断变化的流动通道，从而导致突破压力的增大，因此有机质及其中烃类的生成能够提高盖层的封盖性能。当泥页岩盖层中的流体为气水/油水混合相时，其突破压力在多种机制的作用下，与盖层厚度存在正相关性。在低渗油气藏开发中，油气和水的混合分布是形成启动压力梯度的一种重要机制。

Experimental study of the breakthrough pressure of capillaries and the sealing ability of shale

Several experiments were made with mono-capillary-tubes to study how breakthrough pressure of mudstone cap rock changes when there are multiple two-phase interfaces in the flow path. The results indicated that breakthrough pressure is related to diameter but not the length of the capillary tube when there is only liquid phase in the tube. However, with two mixed phases in the tube, the breakthrough pressure slightly increases with the number of two-phase interfaces, and the increase becomes more remarkable when the wettability of tube surface changes from hydrophilic to a mix of hydrophilic and hydrophobic. The results indicated that the sealing ability of black shale could be improved by the presence of organic matter and hydrocarbon generation. Additionally, for shales with two phases in pore system, breakthrough pressure has a positive relation with the thickness of cap rock. This interpretation is different from previous ones with respect to breakthrough pressure being related to the thickness of cap rock. Mixed phases of oil/gas and water is also an important explanation why fluids can only be mobilized when the driving pressure gradient reaches a critical value, which is called starting pressure gradient in low permeability pools.