黏弹性驱替液所产生的微观力对驱油效率的影响

Influence of the micro-force produced by viscoelastic displacement liquid on displacement efficiency

多孔介质中的驱油效率一般是由宏观驱替压力梯度与油水间界面张力的比值来确定的.但是,当宏观驱替压力梯度恒定时,无法用宏观力去解释黏弹性对驱油效率的影响.为此,分析了弹性和非弹性驱替液作用在残余油上的微观力,以及作用在流动的弹性和非弹性流体中各"点"上应力的异同,用数学方法计算了流体支点受到不同大小应力对微观流线的影响,研究了微观流线的改变对作用在微观残余油上的作用力的影响;通过实验证明了在宏观压力梯度不变的条件下,增大的微观力主要作用在孔隙中各种残余油团的突出部位,使突出部位变形并移动.可视岩心模型实验结果证实了上述计算和分析的结论,给出了不同黏弹性流体对岩心驱油效率的影响,以及考虑黏弹性对驱油效率的影响因素后的数模计算结果,并且与现场大规模聚合物驱的效果以及现场密闭取心结果进行了对比.上述数学模拟计算、分析、实验室和现场试验结果都表明,当驱替液的弹性增加时,作用在残余油的微观力也会改变.结果是,在驱替压力梯度恒定的条件下,黏弹性驱替液比非弹性驱替液的驱油效率高.这种用微观流线和微观作用力的分析方法以及所得到的结论应有助于进一步了解多孔介质中驱油效率的机理,有助于优化驱油方案设计,有助于筛选和研制更好的化学驱油剂和分析注入非牛顿流体和凝胶时出现的现象.

The displacement efficiency(De) in porous media is usually determined by the ratio of the macro pressure gradient to the interfacial tension(IFT) between displacement liquid and residual oil.However,when the pressure gradient is constant,it cannot be explained why the viscoelastic displacement liquid can increase the displacement efficiency.Therefore,the micro-forces acting on residual oil by elastic displacement liquid and inelastic displacement liquid,and the difference between the stresses acting on 'the fulcrums' in the elastic fluid and the inelastic fluid flowing are analyzed.The effect of the stress difference on the micro-flow-line in pores is simulated,and the affect of the change of the micro-flowline on the micro forces acting on residual oil is shown.Experiments show that when the macro pressure gradient is not changed,the increased microforce acting on the protruding part of different types of the residual oil drop group in pore makes the protruding part deform and makes the residual oil drop group move.The conclusion is proven by visual core model.The effects of different viscoelastic displacement fluids on the displacement efficiency of cores,and the numerical simulation result in which the effect of viscoelasticity on the displacement efficiency is considered are presented.They are compared with field large-scale displacement results and field sealed coring results.The mathematical simulation result,analysis result,experimental results and field results all shown that,the microforce acting on residual oil will change when the elasticity of the displacement fluid is increased,and therefore the displacement efficiency of viscoelastic displacement fluid is higher than that of inelastic displacement fluid.The analysis method of micro-flowline and micro-force and the conclusions drawn from this paper will be helpful to further understanding the displacement mechanism in porous media,be helpful to optimizing oil displacement plan design,be helpful to screening and developing better displacement agents,and helpful to analyzing the phenomena associated with the injection of non-Newtonian fluid and gel.