考虑污染条件下页岩气储层气-水两相渗流机理研究

Shale gas, as the realistic unconventional gas resource, which plays an important role in ensuring national energy security by strengthening its basic theoretical innovation, accelerating its exploration and development and achieve the high-efficiency development technology. Currently, large-scale hydraulic fracturing technology is applied to develop shale gas. Reservoir pore structure will become more complex after the reservoir is exposed to fracturing fluids. The main reason is the shale will soften and swell under wetting, and filter liquid will block the shale formation and will react chemically with petrographic composition to form precipitates. Therefore, it is very important to predict shale gas productivity, evaluate fracturing effect and make plans for shale gas development by doing research on the seepage mechanism under the condition of formation damage in shale gas reservoir. In this subject, a set of theories and methods system will be formed to measure nanoscale pore structure parameters and physical property parameters in shale gas reservoir, and to simulate gas-water two phase flow in fracture media. Desorption mechanism of organic matters in reservoir and micro seepage mechanism in pore-fracture and the influence of formation damage on gas flow will be revealed in this research. We will propose a method to evaluate the formation damage after fracturing and establish a mathematical model of nonlinear unstable fluid-solid coupling which takes formation damage into consideration. Those research results will provide theoretical and scientific basis for shale gas development.

页岩气作为最现实的非常规天然气资源，强化基础理论创新、加快勘探开发步伐、形成高效开发技术对保证国家能源安全有着重要意义。 目前页岩气开发多采用水平井大规模水力压裂技术。页岩气储层与压裂液接触后储层孔隙结构将会更加复杂，主要原因是页岩遇水软化膨胀、滤液堵塞页岩储层孔隙、滤液与岩石成分发生物理化学反应生成沉淀。因此研究页岩气储层考虑污染条件下渗流机理对准确预测产能、评价压裂效果、指导开发方案设计等至关重要。 本课题研究将形成一套系统页岩气储层纳米级孔隙结构参数与物性参数测定方法、气体-水两相流动数值模拟方法，揭示页岩气储层有机质解吸机理、基质岩石孔隙-裂缝微观渗流机理及储层伤害对渗流的影响，给出页岩气储层水力压裂污染评价方法，建立考虑页岩气储层污染条件下非线性不稳定流-固耦合渗流数学模型，为页岩气储层开发方案设计提供理论基础和科学依据。

形成了一套系统的页岩气储层基质、有机质、天然微裂缝的孔隙结构参数测定方法，给出了考虑压裂液污染的龙马溪组页岩储层微观孔隙结构参数范围。测定了页岩气储层岩石渗透率—应力敏感性、污染条件下页岩渗透率及滑脱系数、污染条件下页岩吸附解吸规律、页岩储层裂缝长期导流能力，形成一套系统的页岩气储层物性参数测定方法并给出页岩气储层污染前后岩石物性参数变化规律。基于改进的马尔科夫链蒙特卡洛方法（MCMC方法）、泰森多边形拓扑理论、岩石弹性力学理论，建立了考虑应力条件的三维孔隙-裂缝网络模型，为页岩气储层数值模拟计算提供了理论基础。考虑页岩气在孔隙中的吸附解吸、气体滑脱、压裂液污染渗流机理，建立了页岩气储层基质中气-液两相LBM渗流模型。考虑裂缝粗糙度、开度、迂曲度三个裂缝参数，建立了页岩气储层裂缝中气-液两相LBM渗流模型。利用区域分解的方法建立了页岩气多尺度气-液两相流固耦合渗流模型，该模型能够实现模拟页岩气从纳米孔—微米孔—裂缝的连续流动。利用LBM方法建立了页岩气在不同孔隙尺寸下的非线性不稳定流-固耦合渗流模型，通过有限元求解形成了页岩气储层甲烷气体-水两相流-固耦合流动数值模拟方法。本研究成果为后续页岩气储层渗流规律研究、气井产量预测、开发方案设计提供理论基础。