Abstract: The test data of Daqing, Dagang and Bohai oilfields show that the injection profile reversal occurs in injection wells in the middle and later stages of chemical flooding, thus reducing the effect of increasing oil and decreasing water. To explore the injection profile reversal mechanisms of polymer flooding and enhance the development effect of chemical flooding, a physical core simulation method characterized with "separate injection and separate production" was proposed to investigate the injection profile reversal mechanisms of polymer flooding and the countermeasures. The results show that the key to enhancing oil recovery in water-flooding reservoirs is to increase the injection pressure difference in the medium- and low-permeability areas of reservoirs, in which case the injection rate can be improved, the flow resistance of high-permeability areas can be enhanced by increasing the retention of chemical materials, and the flow resistance of low-permeability areas can be decreased by sidetracking drilling or micro-fracturing. In the process of polymer flooding, the increase of flow resistance and injection starting pressure caused by polymer retention in the low-permeability areas of reservoirs will be much higher than that in the high-permeability areas, and the injection pressure is subject to the rock fracturing pressure of reservoirs, which will jointly result in the injection profile reversal in injection well. However, the alternating injection of polymer solutions (binary or ternary composite system)with high and low retention capabilities can reduce the increasing rate of flow resistance and injection starting pressure in the low-permeability areas of thick oil layers and then will lower the rate of injection profile reversal. Field tests indicate that the alternating injection of oil displacement agents with different retention capabilities can lower the rate of injection profile reversal and enhance the chemical flooding effect in terms of increasing oil and decreasing water.

Key words: heterogeneous reservoir, polymer flooding, injection profile reversal, mechanism of action, countermeasures, practical effects

摘要： 大庆、大港和渤海油田的矿场测试资料表明，化学驱中、后期注入井都出现了吸液剖面反转现象，因此降低了增油降水效果。为进一步探究聚合物驱吸液剖面反转机理、提高化学驱开发效果，采用"分注分采"岩心物理模拟方法，开展了聚合物驱过程中吸液剖面反转作用机制和应对方法实验研究。研究结果表明，水驱油藏提高采收率的关键在于增加储层内中、低渗透部位吸液压差，为此可以提高注液速度或利用化学材料滞留增大高渗透部位渗流阻力或采取侧钻和微压裂等措施减小低渗透部位渗流阻力。聚合物驱过程中，聚合物在储层内低渗透部位滞留所引起渗流阻力和吸液启动压力增幅要远大于高渗透部位的水平，加之注入压力受限于储层岩石破裂压力，二者共同作用引起注入井吸液剖面反转现象。采取高滞留与低滞留能力聚合物溶液（或二元和三元复合体系）交替或梯次注入方式可以降低厚油层内低渗透部位渗流阻力和吸液启动压力升高速度，进而减小吸液剖面反转速度。矿场试验表明，不同滞留能力驱油剂交替或梯次注入减小了吸液剖面反转速度，提高了化学驱增油降水效果。

关键词: 非均质油藏, 聚合物驱, 吸液剖面反转, 作用机制, 应对措施, 实践效果