Abstract: In this paper,the visco-elastic characteristics of polyacrylamide solution have been studied experimentally.Based on the forms of residual oil after water flooding in porous media and flowing behavior of polymer solution,the mechanisms of the effect of polymer solution with visco-elastic characteristic on each type of residual oil after water flooding had been analyzed and the mechanisms of polymer solution with visco-elastic characteristic increasing microscopic oil displacement efficiency were studied.By the analysis of microscopic experiments of percolating flow,relevant relationships between the characteristic parameter describing the visco-elastic behavior of polymer solution and displacement efficiency of residual oil in "dead ends" were given.It is shown that the larger the visco-elastic behavior of polymer solution,the higher the displacement efficiency of residual oil in "dead ends".The residual oil can be pulled into "oil threads" by the polyacrylamide solution,and a new type of oil flow channel,i.e."oil thread" channel,can be formed and residual oil flows downstream through the "oil thread" channel.The probability of forming a steady "oil thread" flow channel in polymer flooding was also analyzed theoretically and proved.The research result indicates that the mechanism of polymer solution microscopically increasing oil recovery is due to the visco-elastic characteristic of the polymer solution,the sweeping force acting on the residual oil by the visco-elastic polymer solution is larger than that of water.The residual oil was not pushed out by the polymer solution but pulled out by the polymer solution.It is also found that every type of residual oil after water flooding can be decreased by visco-elastic polymer solution,and the larger the visco-elastic property,the stronger the capability of the polymer solution to “sweep out”the residual oil.

Key words: polyacrylamide solution, rheological characteristic, viscous-elastic behavior, oil displacement efficiency, mechanism

摘要： 实验研究了水解聚丙稀酰胺溶液的粘弹性,分析了粘弹性聚合物溶液对残余油的作用机理,研究了粘弹性聚合物溶液提高残余油驱替效率的机理.根据微观渗流实验,建立了描述聚合物溶液粘弹性的特征参数与孔隙盲端中残余油驱替效率的对应关系,粘弹性越强,对盲端中残余油的驱替效率越高.聚合物溶液可将残余油拉成“油丝”,形成新的油流通道——“油丝”通道,文中理论分析并证明了聚合物溶液的粘弹性可以形成稳定的“油丝”油流通道.研究结果表明,聚合物驱提高微观驱油效率的机理是由于聚合物溶液的粘弹特性,残余油是被聚合物溶液拉出来的,而不是推出来的.粘弹性的聚合物溶液均会不同程度地降低各类残余油量,粘弹性越大,携带出的残余量越大,驱替效率越高.

关键词: 聚丙稀酰胺溶液, 流变性, 粘弹性, 驱油效率, 机理