压敏效应对致密裂缝油藏渗流影响的实验研究

Experimental Study on Influence of Pressure Sensitive Effect on Seepage in Tight Fractured Reservoirs

致密油藏开发过程中,原油的产出会造成地层压力供给不足,作用在岩石骨架上的有效应力增加,岩石骨架发生形变,渗透率降低,从而影响流体的流动及产能,给高效、综合地开发油藏带来诸多问题。以渤海湾盆地济阳坳陷岩样为例,通过分析致密砂岩储层材料的组成、裂缝发育、孔隙结构等影响应力敏感性的因素,通过改变围压的大小,模拟地层中岩石骨架受力情况,明确不同有效应力和岩石渗透率的变化关系。结果表明:敏感性曲线分为两个阶段,第一阶段渗透率递减率大于30%,主要是由于裂缝在压力作用下的假塑性变形;第二阶段渗透率下降小于30%,在这一阶段,弹性变形主要取决于岩石基质孔隙的塑性变形。第二阶段对于应力变化较为敏感,因此应用第二阶段评估储层应力敏感性更为实用,并且建立了压敏模型。

In the process of tight reservoir development, the production of crude oil will cause insufficient formation pressure supply, increase the effective stress acting on the rock skeleton, deform the rock skeleton and reduce the permeability, which will affect the fluid flow and productivity, and bring many problems to the efficient and comprehensive development of the reservoir. Taking the rock sample of Jiyang depression in Bohai bay basin as an example, the factors affecting stress sensitivity were analyzed, such as material composition, fracture development and pore structure of tight sandstone reservoir. The stress of rock skeleton in the formation was simulated by changing the confining pressure, and the relationship between different effective stresses and rock permeability was defined. The results showed that the sensitivity curve was divided into two stages: in the first stage, the permeability decline rate was greater than 30%, which was mainly due to the pseudoplastic deformation of the fracture under pressure. In the second stage, the permeability decreased by less than 30%. In this stage, the elastic deformation mainly depended on the plastic deformation of the pores of the rock matrix. The second stage was sensitive to stress change, so it was more practical to evaluate the stress sensitivity of reservoir in the second stage, and a pressure-sensitive model was established.