聚合物流变性对非均质油藏波及效率的影响

Effects of Polymer Rheology on Sweep Efficiency of Heterogeneous Oil Reserves

研究聚合物溶液的流变性与其在非均质油藏中渗流特性之间的关系,可为进一步发挥聚合物驱在海上油田的应用效果提供理论依据。结合海上某油田砂岩稠油油藏实际的非均质性特征,研制出一种能在高压下模拟驱油体系在油藏深部渗流的层内非均质性二维可视填砂模型,实验筛选出同一剪切速率下,剪切黏度近似相等,但流变性差异较大的3种驱油体系,并以固定剪切速率的注入方式进行渗流实验。实验表明,3种驱油体系驱替后,在模型中均呈现楔形的剩余油分布状态,但透光面积和渗流规律存在较大差异。聚合物溶液的流变性能够延缓注水进入无效循环的阶段,从而改善低渗透层的水驱油波及效率,表现为幂律指数n越小,波及效率越高。

Studies on the relationship between polymer solution rheology and the seepage characteristics in heterogeneous oil reserves provide a useful theoretical basis to improve the efficacy of polymer flooding in offshore oilfields. On the basis of the actual heterogeneity of heavy oil reservoirs in the sandstones of an offshore oilfield, we developed a two-dimensional visual sand-packed model capable of simulating reservoir heterogeneities in the seepage of oil displacement systems within the deeper parts of an oil reservoir, under high pressures. In this work, we performed a rheology experiment using injections with a fixed shear rate on three oil displacement systems. These displacement systems have significantly different rheologies, but similar shear viscosities at the same shear rate. It was shown in this experiment that oil displacement using these three oil displacement systems always resulted in wedge-shaped residual oil distributions within the similitude model. However, there were significant differences between these systems in their transparent areas and seepage patterns. It was shown that polymer solution rheology can delay the onset of ineffective cycling during fluid injections, thus improving the sweep efficiency of oil displacement in low-permeability reservoirs, resulting in increases in sweep efficiency with decreases in the power law exponent, n.