低渗透致密油藏压裂驱油剂润湿性评价及效果

针对低渗透致密油藏压裂驱油剂的润湿性评价问题，分析现有接触角法的误差及不确定性，提出了评价压裂驱油剂润湿性的改进方法，采用润湿倾向指数，即驱油剂与蒸馏水在亲水/油表面的润湿接触角的比值来表征压裂驱油剂的润湿性改变方向和程度。结果表明，用接触角和接触角变化的最大值反映驱油剂对储层润湿性改变方向和能力都存在一定的不确定性。亲水表面的性质非常稳定，润湿接触角偏差较小，但亲油表面的润湿接触角偏差较大。蒸馏水与亲水/油表面润湿接触角的相对平均偏差分别为0.281%、8.929%。另外，部分驱油剂在亲水/油表面的接触角最大变化值差异不明显。用润湿倾向指数可较好地表征驱油剂的润湿性改变程度。润湿倾向指数不确定度远小于接触角不确定度。0.2%磺酸盐类驱油剂、聚氧乙烯醚类驱油剂、氟碳类驱油剂在亲水表面的接触角（润湿30 s）不确定度分别为1.24、3.11、0.64，而水润湿倾向指数不确定度分别为2.48×10^-2、6.33×10^-2、1.76×10^-2。通过Amott 方法，测得7 种压裂驱油剂作用下天然岩样的水湿指数。该水湿指数从大到小的排序与用接触角法测得的水润湿倾向指数从小到大的顺序一致。两种方法的测试结果进一步证实了使用润湿倾向指数的准确性和优越性。该方法有利于快捷地评价压裂驱油剂对储层润湿性的改变能力，优选低渗透致密油藏压裂驱油剂。

Wettability Evaluation and Effect of Fracturing Oil Displacement Agent in Low-permeability Tight Reservoirs

Aiming at the wettability evaluation of fracturing oil displacement agents in low-permeability tight reservoirs，the errorand uncertainty of the existing contact angle method were analyzed. An improved method for evaluating the wettability of fracturing oil displacement agents was proposed. The wettability tendency index，i.e.，the ratio of wetting contact angle between oildisplacement agents and distilled water on the hydrophilic/lipophilic surfaces，was used to characterize the wettability changedirection and degree of fracturing oil displacement agents. The results showed that there was some uncertainty in reflecting both thedirection and ability of the oil displacement agent to change the reservoir wettability by the contact angle and the maximum value ofthe contact angle change. Hydrophilic surfaces were very stable and had small deviations in wetting contact angle，while lipophilicsurfaces had large deviations in wetting contact angle. The relative average deviations of the wetting contact angles between distilledwater and hydrophilic/lipophilic surfaces were 0.281% and 8.929%，respectively. In addition，the differences in the maximumchange values of contact angles of some oil displacement agents on hydrophilic/lipophilic surfaces were not obvious. The wettabilitychange degree of oil displacement agents could be better characterized by wetting tendency index. The uncertainty of wettingtendency index was much smaller than that of contact angle. The uncertainties of contact angle（wetting for 30 s）of 0.2% sulfonateoil displacement agents，polyoxyethylene ether oil displacement agents and fluorocarbon oil displacement agents on hydrophilicsurfaces were 1.24，3.11 and 0.64，respectively，while their uncertainties of water wetting tendency index were 2.48×10^-2，6.33×10^-2 and 1.76 × 10^-2，respectively. The water-wetting index of natural rock samples under the effect of seven fracturing oildisplacement agents was measured by the Amott method. The order of this water-wetting index from largest to smallest wasconsistent with the order of water-wetting tendency index from smallest to largest measured by the contact angle method. The testresults of both methods further confirmed the accuracy and superiority of wetting tendency index. This method was beneficial forquickly evaluating the ability of fracturing oil displacement agents to change reservoir wettability and for preferentially selectingfracturing oil displacement agents for low-permeability tight reservoirs.