清洁压裂液返排液对致密油藏自发渗吸驱油效果的影响

针对清洁压裂液返排液回收利用率低、处理困难的问题,并结合致密油藏渗吸采油机理,以处理后的现场清洁压裂液返排液作为渗吸液,开展清洁压裂液返排液对致密油藏自发渗吸驱油效果的影响研究。结果表明:选择渗吸液浓度时,不仅要考虑降低黏附功、提高洗油效率,还要兼顾界面张力和润湿性对毛细管力的影响,当渗吸液质量分数为50%时,渗吸采收率最大可达27. 5%,此时毛细管力作为渗吸驱油的动力占据主导地位,渗吸强度较大;随着岩心渗透率增加和实验温度升高,渗吸采收率逐渐升高。天然岩心渗吸—核磁联测实验结果显示,2块天然岩心的渗吸采收率均可达到26%左右,渗吸初始阶段,油水置换速度较快,渗吸采收率迅速上升,20 h后渗吸速度下降直至渗吸结束。清洁压裂液返排液能够提高致密油藏自发渗吸采收率,为该类压裂液返排液重复利用提供了一种新思路。

Influences of the clean fracturing flow-back fluid on the oil displaced effect of the spontaneous imbibition in dense reservoirs

Aiming at the problems of the low recovery-utilization rate and difficult to handle for the clean fracturing back-flow fluid, and combined with the imbibition oil producing mechanism in the tight reservoir, regarding the treated field clean fracturing back-flow fluid as the imbibing fluid, the influences of the clean fracturing back-flow fluid on the spontaneous imbibition and flooding effects of the tight oil reservoir were studied. The results show that when selecting the concentration of the imbibing liquid, reducing the adhesion work and improving the cleaned efficiency are not only considered, the impacts of the interfacial tension and wettability on the capillary force should be also taken into account, when the concentration of the imbibition is 50%, the maximum imbibition recovery can reach 27.5%. At this time, the capillary force takes the dominant position for the imbibition oil flooding, the imbibition strength is pretty larger;with the increases of the core permeability and the experimental temperature, the imbibition recovery increases gradually. The results of the natural core imbibition-magnetic testing experiment show that both imbibition recoveries can up to 26% or so for two pieces of the natural core, at the initial stage of the imbibition, the oil-water replaced and displaced speed is greatly rapid, the imbibition recovery rises fast, after 20 h, the infiltration rate decreases until the end of the imbibition. The clean fracturing back-flow fluid can improve the spontaneous imbibition recovery of the tight oil reservoir, thus a new idea is provided for the reutilization of this type of back-flow fracturing fluid.