致密油储层纳微米孔隙介质非线性渗流机理研究

Nano/micron scale pore are widely distributed in tight oil reservoir. The seepage law existed for the tight oil reservoir matrix could not reflect the real flow character of the porous medium, which is not based on fluid mechanics theory, nor from microscopic perspective. This fund use three kinds of methods：experiment measurement, fluid mechanics theory analysis and micro pore network model(PNM) numerical simulation, to explore the microscopic percolation mechanism of the tight oil reservoir from three aspects: the fluid properties, pore structure character and liquid-solid interface reaction. Including the following steps: First，the fluid mechanics models are established for single phase liquid and oil-water immiscible two-phase flow in nano/micron circular tube considering the coupling interaction of liquid properties and liquid-solid interface reaction. Then, based on the above theory and combined the pore structure character from the experiment testing and measurement, the single-phase liquid and water flooding oil two phase flow PNM are simulated, The influencing mechanisms of those porous structure factors are revealed for liquid flow in nano/micro porous media; Last, Comparative analysis of simulation results and the seepage experiment results, the nonlinear seepage mechanisms due to the comprehensive coupled factors are revealed for single-phase liquid and water flooding oil two phase flow in nano/micro porous media, the non-linear seepage equation of single phase liquid for tight oil reservoir matrix is confirmed, those can provide accurate theoretical basis for numerical reservoir simulation of tight oil, and provide important theoretical guidance for improving the matrix seepage process after hydraulic fracturing even for developing tight oil reservoir efficiently.

致密油储层发育丰富的纳微米级孔隙，现用的致密油储层基质的渗流理论，没有从流体力学基础理论和微观角度出发，不能反映孔隙介质内的真实流动规律。本基金采用实验测试分析、流体力学理论分析和纳微米尺度孔隙网络模型(PNM)数值模拟三种方法，从流体和孔隙介质特性及液-固界面作用三方面探索致密油储层非线性机理。具体包括：通过流体力学理论建立纳微米圆管单相液体、油水两相非混相流动的动力学模型，分析液-固界面作用和流体特性相互耦合对其影响机制；以此为基础，结合致密油储层的孔隙结构特征，进行PNM数值模拟，揭示孔隙介质结构参数对单相液体和水驱油两相非线性渗流的影响机制；通过模拟结果与渗流实验结果对比分析，揭示纳微米孔隙介质多因素耦合的单相和水驱油两相非线性渗流机理，并确定致密油储层基质单相液体非线性渗流方程，为致密油油藏数值模拟技术提供理论基础，并为水力压裂后改善基质渗流过程及致密油的高效开发提供理论依据。

致密油是我国非常规石油资源最现实的接替领域，但致密油藏孔喉处于纳微米级，孔隙度小，渗透率低，渗流阻力大。本项目采用实验测试、流体力学理论分析和纳微米尺度孔隙网络模型(PNM)数值模拟方法，对致密油纳微米孔隙介质进行了如下研究工作。.（1）进行了致密储层岩心的孔隙度渗透率测试，进行了单相渗流实验和启动压力梯度测试，为后续工作提供实验依据；.（2）推导并简化了液固界面长程范德华力形式，将其加入流体力学方程，并考虑含溶解气的流体的微可压缩性，采用涡流函数、正则摄动法等求解方程组的近似解析解，流速低于与泊肃叶流动，但流速和压力梯度仍呈线性关系；再分析了宾汉流体和静电作用引起的电黏滞力的纳微圆管流动，结果显示两者都能降低流速，但宾汉性能引起启动压力梯度（TPG）和非线性特征，电黏滞力增强非线性程度；最后建立了考虑四种因素的润湿微圆管流动，得到了低速非线性流动模型，结果与去离子水在氧化硅微圆管流动实验吻合，可推测牛顿流体在纳微尺度下变为了宾汉流体；并将模型扩展到多孔介质，模型结果与多个岩心流动渗流曲线、TPG和可动流体直径下限（Rm）相吻合，误差小于9%，地层压力下，Rm在10~30nm之间。.（3）建立了纳微米圆管内无动界面的水驱油两相流动输运模型，并研究了以上四个因素对两相流动的影响；并构建了考虑流体微可压缩性、电黏滞力和范德华力的3维孔隙网络模型，模拟了单相和水驱油两相的渗流过程，发现考虑微观作用单相流速会降低，两相流动见水点后移，降低幅度较小，但降低接触角和增加油水界面张力能明显增强水驱油过程。.项目从微观作用和流体性质角度分析了纳微孔隙的流动特征，阐释了致密油藏低速非线性渗流机理，流速降低是由于微观作用力、微可压缩性和宾汉塑性共同引起的，TPG和Rm及非线性特征主要由宾汉塑性引起，宾汉塑性存在时也受微可压缩性和范德华力的影响。该项目探明了致密油藏非线性渗流特征的机理，并寻找到了降低流动阻力的方法从而指导油藏开发提高采收率。