低渗致密油藏重复压裂用渗吸液的研究与应用

Research and application of re-fracturing with imbibition technology in low permeability and tight oil reservoir

目的桩西低渗致密油藏压裂投产后单井产能下降快,重复压裂效果差。为改善桩西低渗致密储层开发效果,提出并研究形成了渗吸液作为辅助液的压裂技术。方法室内实验评价了渗吸液对含油致密岩心的渗吸作用,以及对岩心驱替效率的影响,测定了不同含量下渗吸液的油水界面张力和润湿角。结果渗吸液将油水界面张力降至2.6×10^(-2)mN/m,并将水对岩石润湿角118.3°的弱亲油储层润湿性转化为水对岩石润湿角63°的弱亲水性储层。结论通过添加渗吸液可大幅提高渗吸液驱替效率、渗吸速率和采收率,这是渗吸液辅助重复压裂技术日产油量增加和延缓产量递减的主要机理。渗吸液质量分数升高至0.5%后,提升效果变缓。2021年渗吸液辅助重复压裂技术现场实施5井次,与同区块5口常规重复压裂井相比,累计年增油5451 t。该研究对低渗致密储层压裂改造具有指导作用。

Objective After fracturing and putting into production of the low-permeability tight oil in reservoir Zhuangxi,the single-well productivity declined rapidly,and the effect of re-fracturing technology was poor.In order to improve the development effect of low-permeability tight reservoirs in Zhuangxi,the fracturing with imbibition technology was proposed and studied.Methods Through laboratory experiments,the imbibition effect of imbibition fluid on oil-bearing tight cores and its effect on core displacement efficiency were evaluated,the oil-water interfacial tension and wetting angle of different concentrations of imbibition fluid were measured.Results The imbibition fluid reduces the oil-water interfacial tension to 2.6×10^(-2) mN/m,and transforms a weakly oleophilic reservoir with a water-to-rock wetting angle of 118.3°to a weakly hydrophilic reservoir with a water-to-rock wetting angle of 63°.Conclusions The addition of imbibition fluid can significantly improve imbibition repellency efficiency,imbibition rate and recovery,which is the main mechanism of increasing daily oil production and slowing production decline with permeate-assisted repetitive fracturing.The upgrading effect becomes slower after the imbibition fluid concentration rises to 0.5%.In 2021,the imbibition-assisted re-fracturing technology was implemented in 5 wells,and the cumulative annual oil increase was 5451 t compared with 5 conventional re-fracturing wells in the same block.This study is a guideline for fracture modification of low permeability tight reservoirs.