作为页岩油藏开发的一种关键技术手段,压裂阶段的动态渗吸驱油在近年来已成为油藏工程研究的热点.鉴于全球能源需求以及对非常规油气资源的持续勘探,这项技术在提高页岩油藏开采效率方面的重要性不容小觑.然而,页岩油储层动态渗吸过程中,不同因素在动态渗吸各个阶段的具体作用机制尚不明确,各因素对渗吸驱油效果的影响难以精确量化,严重制约了页岩油藏开发效率的进一步提高,导致开发成本上升,同时给资源的可持续开发带来了挑战.针对页岩油储层动态渗吸机理及作用规律不清的问题,建立了岩心尺度数值模拟模型,采用控制变量法设置了 15 个模拟方案,揭示了驱替压差、毛细管半径、润湿角、油水粘度对动态渗吸驱油效果的作用机制,明确了流体渗流变化规律.研究表明:动态渗吸中,毛细管半径从 0.1 μm增大至10 μm,毛细管力减小,流体渗吸速率加快,渗吸采收率提高了8.0%;驱替压差从 0 MPa开始增大,渗吸由静态升级为动态,3 MPa时渗吸采出程度提高了7.9%;认为驱替压差与采出程度符合幂函数关系,存在最优驱替压差.岩心润湿性由亲水向中性、亲油变化,采出程度由水润湿的 48.9%下降到油润湿的 33.9%;原油粘度由53.30 mPa·s降低至 13.99 mPa·s,渗吸采收率提高了 9.1%;驱替相粘度越大,初始渗吸速度越小,但渗吸驱油效果越好.现场操作中可通过优化注入压力,选择合适的压裂液、表面活性剂等,提高亲水程度和驱替相粘度,改善动态渗吸过程,从而增大驱油效率.未来应进一步考虑多相流动的复杂性,同时结合储层的非均质性,从不同尺度研究各因素对页岩动态渗吸过程的影响.

As a critical technical approach for shale reservoir development,dynamic imbibition displacement during the fractur-ing stage has emerged as a focal point in reservoir engineering research over recent years.In light of global energy demands and ongoing exploration of unconventional oil and gas resources,the significance of this technology in enhancing the exploitation of shale oil reservoirs cannot be overstated.However,the specific mechanisms of dynamic imbibition process in shale oil reservoirs influenced by various factors still aren't unclear,and it's difficult to accurately quantify their impact on imbibition oil production efficiency.These uncertainties significantly hinder further improvement in the development efficiency of shale oil reservoirs,lead to higher development costs and bring huge challenges to sustainable resource development. Aiming at the unclear dynamic imbibition mechanisms and action laws of shale oil reservoir,a core-scale numerical simulation model was established,and the control variable method was adopted to set up 15 simulation schemes.By these methods,the mechanisms of displacement pressure difference,capillary radius,wetting angle and oil-water viscosity of dynamic imbibition displacement effect,and the change laws of fluid seepage were revealed.The effects of displacement pressure difference,capillary radius,wetting angle,and oil-water viscosity on the effectiveness of dynamic imbibition oil recovery,and the laws of fluid seepage changes were clarified in this study.The results show that:During dynamic imbibition,as the capillary radius increase from 0.1 μm to 10 μm,capillary force decrease and fluid seepage rate accelerates,leading to 8.0%increase in imbibition recovery.Along with the displacing pressure difference increases from 0 MPa to 3 MPa,the imbibition upgrades from static to dynamic,and the imbibition recovery degree increases by 7.9%.It is considered that the displacing pressure difference and the recovery degree are in accordance with the power function relationship,and there is an optimal displacing pressure difference.With changes in rock wettability from hydrophilic to neutral or oleophilic,extraction degree decreases from 48.9%for water-wet conditions to 33.9%for oil-wet conditions.As crude oil viscosity decreases from 53.3 mPa·s to 13.99 mPa·s,imbibition recovery rate increases by 9.1%;the higher the viscosity of water phase,the smaller the initial imbibition velocity,but the better the imbibition displacement effect.In oil field operation,by optimizing injection pressure,selecting suitable fracturing fluid and surfactant,the hydrophilic degree and displacement phase viscosity can be improved,and the dynamic imbibition process can be improved to increase the oil displacement efficiency.In the future,the complexity of multiphase flows and the heterogeneity of reservoirs should be further considered to study the influence of various factors on the dynamic imbibition process of shale from different scales.