页岩储层离子扩散特征及影响因素分析

Analysis of Ion Diffusion Characteristics and Influencing Factors in Shale Reservoirs

页岩储层压裂返排液中矿化度有明显升高,这与页岩储层离子扩散能力有关。目前,尚没有定量表征页岩储层离子扩散能力的方法。基于此,提出一种评价页岩离子扩散能力的方法,并分析其影响因素。结果表明:页岩储层中黏土矿物含量越高,离子扩散速度越快,持续时间越长。尤其是蒙脱石,其孔隙结构遇水发生反应,盐离子迅速扩散,会引起储层中压裂液矿化度的升高;盐溶液和表面活性剂也会对页岩储层的离子扩散能力有明显影响,但影响方式有诸多不同。Na+和K+通过压缩黏土扩散双电层厚度来降低页岩在溶液中的离子扩散能力,此外,K+还能进入页岩硅氧四面体中,阻止盐离子扩散;活性剂会引起溶液分子间作用力的改变,降低页岩在溶液中的离子扩散能力。通过页岩储层离子扩散实验对认识页岩储层裂缝发育程度和页岩储层性质具有重要的工程意义。

The salinity in the shale reservoir fracturing fluid has increased significantly,which is related to the ionic capacity of shale reservoirs.At present,there is no method for quantitatively characterizing the ionic diffusion ability of shale reservoirs.Based on this,a method for evaluating the shale ion diffusion capacity was proposed,and its influencing factors were analyzed.The results show that the higher the clay mineral content in the shale reservoir is,the faster the ion diffusion rate is and the longer the duration is.In particular,the pore structure of montmorillonite reacts with water,and then the salt ions diffuse rapidly,which will cause the salinity of the fracturing fluid in the reservoir to increase.The salt solutions and surfactants also have a significant effect on the ion diffusion capacity of shale reservoirs,but there are many different affecting ways.Na+and K+reduce the ion diffusion capacity of the shale in the solution by compressing the thickness of the electric double layer.In addition,K+can also enter the shale silica tetrahedron,preventing the diffusion of salt ions.The active agent causes a change in the force between the molecules of the solution,and reduces the ion diffusion ability of the shale in the solution.The shale reservoir ion diffusion experiment has important engineering significance for understanding the shale reservoir fracture development and shale reservoir properties.