聚合物分子尺寸与油藏孔喉的配伍性

Compatibility between polymer molecular size and pore throat in reservoirs

驱油用水溶性聚合物分子流经多孔介质时经受孔喉尺寸的自然选择作用。根据“架桥”原理，可对孔喉形成较稳定堵塞的聚合物分子水动力学半径（Rn）与孔喉半径（R）的关系为：Rn大于0．46R。通常，适于聚合物驱油藏的平均孔喉半径中值约为4～16Mm。聚合物分子尺寸的归一化权重分布函数在10nm至数百纳米出现主分布峰，并可能带有水动力学半径为10^3nm数量级或更大的次分布峰。聚合物分子线团越大，在矿化度上升、溶液电场加强后越易被压缩。超大聚合物分子被压缩后使归一化权重分布函数主峰向分子尺寸更大方向移动。梳形聚合物分子结构的改性增强主链刚性，使水动力学半径升高，产生增黏效果。与分子量和水解度相近的聚丙烯酰胺相比，梳形聚合物溶液的增黏幅度高于水动力学半径变化程度。聚合物驱中水动力学半径大于10^3nm数量级的聚合物分子易造成孔喉半径较小的部分多孔介质堵塞，使用清水配制聚合物溶液时此现象更严重。

In polymer flooding, polymer molecules undergo sifting by pore throats when passing through porous media. According to the ＂bridging＂ principle, the relationship between the hydrodynamic radius （Rh） of molecule that can block pore throat and the radius of pore throat （R） is： Rh〉0. 46R. The median of average radii of pore throats in reservoirs suitable for polymer flooding ranges from 4μm to 16μm. The main peak of normalization weighting distribution function （f （Rh）） relating to the size of polymer molecular clew appears in the range of 10nm to hundreds of nm, sometimes with a secondary peak in which Rh is thousands of nanometers or even bigger. With salinity increasing and electric field strengthening in solution, the bigger the size of the clew, the easier is it to be compressed. The compression makes the peak of f （Rh） move to the direction of bigger molecular size. The molecular structure modification of comb-shape polymer （CP） boosts the rigidity of backbone chain, as a result, the Rh of CP and accordingly the viscosity of solution increase. Compared with HPAM with almost the same molecular weight and degree of hydrolysis, the change of viscosity of CP solution is a bit bigger than that of Rh. Polymer molecular clews with Rh of thousands of nanometers or bigger can block the porous medium with small pore-throat radius, especially when the polymer solution is prepared with fresh water.