表面活性剂在致密油藏裂缝-微纳米孔隙中的多尺度渗吸驱油机理研究

The oil recovery of tight oil reservoirs after large scale fracturing is less than 10%, and it is a great challenge to explore potential of tight oil further. Surfactant can significantly improve oil displacement performance of spontaneous imbibition between fracture and matrix, but the imbibition mechanism of surfactant in complex network formed by artificial fracture, natural fissure and matrix micro-nano pores is unclear. With the multi-scale distribution characteristics of fractures and micro-nano pores in the tight oil reservoirs after fracturing, this project will built the multi-scale digital rock which can describe the fractures, nano pores and micro pores in matrix through multi-scale CT Scanning, and then study the micro-nano scale imbibition mechanism of surfactant using fracture and micro-nano pore complex network. Meanwhile, the equivalent double-fractal model of fractures and micro-nano pores will be constructed. Combining the experiments of surfactant imbibition in fractured tight core samples, the mathematical model of surfactant imbibition in fracture and tight matrix of tight oil reservoir will be developed, and the law of surfactant imbibition in fracture and tight matrix will be revealed and the influencing factors will be clarified. The research achievements of this project will be useful for the making development planning of tight oil reservoirs based on the imbibition mechanism and surfactant screening, and it is significant for enhancing tight oil recovery.

致密油藏大规模压裂后采收率不足10%，如何进一步挖掘致密油潜力是目前开发的难点。表面活性剂可以大幅度提高裂缝与基质间渗吸驱油效果，是最有潜力的提高致密油藏采收率的方法之一。但表面活性剂在由人工裂缝、天然裂缝、基质微纳米孔隙组成的复杂网络中的渗吸驱油机理尚不明确。本项目针对致密油藏压裂后裂缝与微纳米孔隙多尺度分布的特征，通过多精度CT扫描，构建能同时表征裂缝、微米孔隙、纳米孔隙的多尺度数字岩心，运用裂缝-微纳米孔隙复杂网络模型探究表面活性剂微观渗吸驱油机理。同时基于分形理论，构建裂缝-微纳米孔隙等效双重分形介质模型，结合裂缝性致密岩心渗吸实验，构建岩心尺度表面活性剂在裂缝-致密油基质中的渗吸驱油数学模型，揭示表面活性剂在裂缝-致密油基质中的渗吸驱油规律并明确其影响因素。本项目研究成果将有助于基于渗吸机理的致密油藏开发方案设计和表面活性剂筛选，对提高致密油藏采收率具有重要意义。

自发渗吸是致密油藏重要的提高采收率机理。表面活性剂可以大幅度提高渗吸驱油效果，但表面活性剂在人工裂缝、天然裂缝、基质微纳米孔隙组成的复杂网络中的渗吸驱油规律尚不明确。本项目综合高压压汞、核磁共振、CT与FIB-SEM扫描等多种测试技术，阐明了致密油藏孔隙结构特征，明确了不同分形模型计算得到的分形维数的物理意义、适用范围与假设条件。考虑复杂裂缝网络的分叉和迂曲特性，将复杂裂缝网络等效为具有分形特征的迂曲二叉树裂缝网络模型，推导得到克氏渗透率、表观气体渗透率和滑脱因子表达式，明确其渗流规律及应力敏感特征。开展了表面活性剂在裂缝性致密岩心中的自发渗吸驱油实验，揭示了裂缝-致密油基质自发渗吸驱油规律，明确了影响渗吸驱油效率的主控因素。考虑表面活性剂吸附和扩散机理，对微纳米孔喉中自发驱油过程开展力学分析，建立了表面活性剂自发渗吸驱油力学模型，定量表征了毛管力在渗吸驱油过程中的动态变化，阐明了表面活性剂吸附和扩散作用对渗吸驱油影响机制，实现了浮力在表面活性剂溶液渗吸驱油贡献的定量表征。构建了致密油藏注水开发机理判定图版，定量表征了驱替和渗吸作用在注水开发中的贡献。创新构建了考虑重力作用的裂缝自发渗吸新模型，明确了重力对润湿相流体在裂缝中自发渗吸的影响，建立了可以定量表征重力对裂缝中自发渗吸影响的诊断图版。对裂缝中水自发渗吸驱油过程进行了研究，得到了裂缝自发渗吸油水前缘解析解，构建了岩心尺度裂缝自发渗吸驱油数学模型，阐明了裂缝分布特征对自发渗吸驱油速率的影响。依托本项目共发表研究论文34篇，其中SCI检索21篇，EI检索7篇；申请发明专利8项，已授权4项，获得中国发明协会发明创业奖成果奖一等奖1项；培养研究生11名。本项目研究成果可以为致密油藏复杂裂缝网络表征与渗吸驱油机理提供理论指导，对致密油藏提高采收率具有重要意义。