低渗透油藏超临界CO2、油和水微观渗流机理研究

Carbon dioxide flooding in low-permeability oil reservoir for enhanced oil recovery not only reduces greenhouse emissions but also awards economical benefits. However, since the pore and throat of low-permeability oil reservoir is tiny, fluid seepage occurs at the microscale, and the microscale effect is distinct. It is difficult for macroscopic methods to accurately describe this issue, therefore, the study of three-phase seepage mechanism from the microscopic points of views in low-permeability oil reservoir has important scientific significance and practical value to improve oil recovery of low-permeability oil reservoir. The research object is the supercritical CO2, oil and water three-phase flow in low-permeability oil reservoir. Considering the existence of seepage boundary layer, the physical and mathematical model which can accurately describe this process will be established, and a multiphase multi-component LBM model will be proposed. Based on the microscopic pore structure of natural core obtained by the Micro-CT, three-phase fluid flow in low-permeability oil reservoir will be simulated. Through the analysis of the impact of seepage boundary layer, water saturation and other factors on the three-phase relative permeability curve and seepage mechanism, the inherent mechanism of non-linear three-phase flow in low-permeability oil reservoir under different wetting system will be revealed. This investigation aims at providing basic theoretical support for the use of CO2-EOR technology to improve oil recovery of low-permeability oil reservoir.

低渗透油藏注CO2驱油既能减少温室气体的排放，又能提高原油采收率获得经济效益。然而由于低渗透油藏的孔隙喉道微小，流体的渗流发生在微米尺度，微尺度效应显著。宏观方法难以准确描述该问题，因此，从微观角度出发，针对低渗透油藏内三相渗流机理进行研究，对提高低渗透油藏的原油采收率具有重要的科学意义和实用价值。本项目以低渗透油藏内超临界CO2、油和水三相渗流过程为研究对象，考虑渗流边界层的存在，建立能够准确描述该过程的物理数学模型，构建相应的LBM多相多组分模型。基于由Micro-CT设备获得天然岩心的微观孔隙结构，对低渗透油藏内三相渗流过程进行模拟。通过分析渗流边界层、含水饱和度等因素对三相相对渗透率曲线及渗流机理的影响，揭示不同润湿体系下低渗透油藏三相非线性渗流的内在机理。本研究旨在为利用CO2-EOR技术提高低渗透油藏原油采收率提供基本的理论支持。

在低渗透油藏，利用CO2驱油既能减少温室气体的排放，又能提高原油采收率获得经济效益。然而由于低渗透油藏的孔隙喉道微小，流体的渗流发生在微米尺度，微尺度效应显著。流体在低渗透油藏内的渗流过程和流体在常规油藏中的渗流过程呈现出明显的差别，实验表明存在启动压力梯度，流体呈现出非牛顿流体特征。本项目考虑微尺度效应及渗流边界层的存在，将流体分为边界层流体和体相流体，边界层流体黏度随距离壁面的距离变化。经过数值模拟实践发现，这样处理方式得到的结果和实验结果相比，误差较大。经过反复研究发现，将渗流边界层内的流体视为非牛顿流体，偏差较小，因此本项目从此角度出发，基于一般化的插值补充格子Boltzmann方法和非牛顿流体的本构方程，建立贴体坐标系下的LBM非牛顿流体模型，开发了相应的计算程序。考虑到低渗透砂岩油层中含有类型丰富的粘土矿物，岩石的表面粗糙度和流动通道尺寸相当，即使是层流状态，粗糙度也会对流体的流动产生影响。因此，研究了表面粗糙度对低渗透油藏内非牛顿流体流动特性的影响规律。此外，通过将非牛顿流体的本构方程引入到LBM多相流模型中，建立非牛顿流体两相流模型，并对非牛顿流体驱替牛顿流体问题展开了研究，为建立完善的低渗透油藏内微观渗流机理奠定了基础。在本项目资助下，共发表期刊论文8篇，其中SCI检索4篇，EI检索5篇；会议论文4篇。2名硕士研究生顺利完成答辩并获得学位，2名硕士研究生预计2016年6月答辩。