海上油田早期注聚聚合物溶液粘弹性分析及地层流变参数计算方法

A viscoelasticity analysis of polymer solution and a method to calculate subsurface rheological parameters for early polymer flooding in offshore oilfields

海上油田井距大、井网不够完善,且平台寿命有限,开展注聚时一般单井注入量相对较大,注入浓度较高,所使用的聚合物分子量较大,因此聚合物溶液在地下的流动行为可能会出现粘弹性效应。基于此,分析了海上油田聚合物驱过程中粘弹性效应影响区域,提出了表征聚合物溶液粘弹性作用范围的临界半径的概念,并且从理论上分析了临界半径随注入强度、松弛时间、幂律指数等参数的变化规律。结果表明,松弛时间越长,临界半径越大;注入强度越大,临界半径也越大;随着幂律指数的增加,临界半径呈现先增大后减小的变化规律。基于粘弹性渗流理论,得到了考虑聚合物溶液粘弹性效应的井底压力差随时间变化的理论关系,据此提出了考虑聚合物溶液粘弹性效应的地层流变参数计算方法。

In offshore oilfields, the polymer flooding is generally larger in single-well injection volume, higher in polymer concentration and heavier in molecular weight of polymer, due to their big well spacing, incomplete well pattern and limited platform life. Thus there may be a viscoelastic effect when the polymer solution flows in subsurface reservoirs. From this consideration, the viscoelastic effect scope was analyzed for the polymer flooding in offshore oilfields, a concept of critical radius that can characterize the viscoelastic effect scope of polymer solution was proposed, and the changes of critical radius with such parameters as injection intensity, relaxation time and power law exponent were analyzed. The results show that the critical radius will increase with extending relaxation time and enhancing injection intensity. With increasing power law exponent, however, the critical radius will firstly increase and then decrease. Based on the theory of viscoelastic flow, a theoretical relationship between pressure difference at borehole bottom and time was derived under consideration of the viscoelastic effect, and a method to calculate the associated subsurface rheological parameters was developed.