低渗透油藏表面活性剂驱微乳液渗流机理及数值模拟研究

The proven reserves of national low permeability reservoir increases year by year. Due to the small pore throat of low permeability reservoir, the high irreducible water saturation, the serious heterogeneity and the existence of start-up pressure, it is difficult to develop low permeability reservoir by conventional water flooding, the producing degree and recovery of water flooding is low. The surfactant field test of Chaoyanggou and Yushulin oil field in Daqing show that, Surfactant flooding can reduce the start-up pressure. But there are differences in the effect of surfactant flooding. Both indoor experiment and field test show that the surfactant flooding process which can produce emulsification has better effect. So we will study the displacement mechanism and percolation rule of the microemulsion after the emulsion of surfactant flooding in low permeability reservoir. We will integrately use the percolation mechanics, physical chemistry, numerical calculation and other multi-disciplinary theory knowledge, apply the experimental analysis and numerical calculation method in this topic. So we can deeply systematic study the formation conditions of the microemulsion for low permeability surfactant flooding and set up the quantitative discriminant standard of microemulsion formation conditions. Combining the physical and chemical parameters of microemulsion flooding, we study the displacement mechanism and percolation rule. So the mathematical model of microemulsion flooding which considering start-up pressure and microemulsion quantitative discriminant conditions is established, and the numerical simulation software is prepared to apply in the field practice to improve and perfect the numerical simulation of surfactant flooding.

全国低渗透油藏探明储量逐年增加，由于低渗透油藏孔喉细小，束缚水饱和度较高，非均质性严重，存在启动压力，常规注水开发难度大，水驱动用程度地、采收率低。大庆朝阳沟油田和榆树林油田表面活性剂驱现场试验表明：表面活性剂驱能够降低启动压力，但表面活性剂驱效果存在差异，室内实验和矿场试验都表明，表面活性剂驱过程能够产生乳化的效果较好，因此本课题将对低渗透油藏表面活性剂驱乳化后微乳液的驱油机理和渗流规律进行研究。本课题将综合运用渗流力学、物理化学、数值计算等多学科理论知识，采用实验分析、数值计算等手段，深入系统地研究低渗透油藏表面活性剂驱微乳液形成条件，建立微乳液形成条件的定量判别标准，结合微乳液驱驱油物理化学参数的测定，研究微乳液驱驱油机理和渗流特征，建立考虑启动压力和微乳液定量判别条件的微乳液驱数学模型，并编制数值模拟软件，并应用于矿场实际中，改进和完善表面活性剂驱的数值模拟方法。

低渗透油藏喉道半径小、贾敏效应严重，存在启动压力梯度，水驱效率低、采收率低，平均只有20%左右，因此，研究微乳液驱提高采收率具有重要的意义。.本项目优选出了低渗透油藏有利于形成微乳液的表面活性剂体系，即3.5%十二烷基硫酸钠+10.0%正丁醇+2.5%盐溶液，为低渗透油藏开展微乳液驱化学用剂筛选提供了参考；针对低渗透油藏孔隙结构特征，明确了岩石润湿性、喉道半径、孔喉分布、矿物组成等地质条件和注入水性质、注入速度、运移距离、含水率级别、段塞大小等开发条件对于微乳液形成的影响，确定了微乳液的形成条件，给出了微乳液形成判别标准：运移距离大于1/3倍注采井距；表面活性剂浓度为0.35%~0.45%；注入液渗流速度为1.2~2.5×10-5cm/s，能够定量判别地下渗流过程中微乳液相存在状态，为建立微乳液驱数学模型提供基础参数；发展改进了定量描述微乳液驱相态变化特征和乳化过程的微乳液相态模型，解决了Hand模型不能精准描述高水/油组分的溶解度曲线、难以获得非对称双结点曲线的解析解、难以直观模拟相态变化过程的问题，提高了相态模拟计算精度；揭示了微乳液提高采收率及活化剩余油机理，结果表明，与水驱相比，微乳液驱能够降低启动压力梯度15%~25%、能够提高油相相对渗透率12%~28%、具有乳化增粘效果，增粘5~10倍，提高采收率16.34~19.88个百分点，为低渗透油藏微乳液驱挖潜剩余油提供了依据；建立了考虑微乳液驱物化过程和启动压力梯度变化的非线性渗流数学模型，编制了微乳液驱油数值模拟软件，为微乳液驱机理研究提供了理论基础，能够科学指导微乳液驱开发方案的编制。.综上所述，本项目解决了低渗透油藏微乳液驱开发的化学剂选择、微乳液形成条件、活化剩余油机理、微乳液渗流规律、微乳液数值模拟等微乳液驱提高采收率技术的关键科学问题，对于低渗透油藏化学驱提高采收率具有重要的理论意义和现实意义。