临界解吸压力约束下的常压页岩气多尺度输运机理研究

常压页岩气藏具有吸附气占比高、微裂缝发育和较快达到临界解吸压力等特点，开采时多尺度输运行为复杂且鲜有专门研究，制约了常压页岩气高效开发。本项目围绕“常压页岩储层微纳孔缝系统多尺度输运行为对地层压力衰减的响应机制”这一核心问题，在明确多尺度微纳孔缝特征及岩石力学性质的基础上，设计实验定量表征地层压力衰减过程中基质和裂缝的输运能力，明确裂缝渗透性对有效应力变化的响应特征和基质纳米孔动态效应；基于地层压力是否达到临界解吸压力，分阶段建立考虑多尺度孔缝空间几何特征、吸附层效应和液相分布状态的储层渗透性评价数学模型，形成常压页岩储层应力敏感评价方法；基于介科学“主导机制间的竞争-协调”原理，揭示微纳孔缝尺度、壁面性质、含液量及分布等多因素影响下的，多种气体输运机制共同参与的常压页岩气多尺度输运机理。研究成果将丰富常压页岩气微观输运理论体系，并可为开发过程中储层保护对策制定、产能预测等提供依据。

Normal-pressure shale gas reservoirs are characterized by high adsorbed gas ratio, developed micro-fractures and rapid reaching critical desorption pressure. The multiscale transport behavior during exploitation is complicated and rarely studied, which restricts the efficient development of normal-pressure shale gas. This project focuses on the response of multiscale transport behavior in micron and nano pores of normal-pressure shale formation to the depletion of formation pressure. Based on the investigation of multiscale pore structure and rock mechanics, the experiments are designed to quantitatively characterize the transport capacity of matrix and fractures during formation pressure depletion. Then the response characteristics of fracture and matrix nano-pore permeability to effective stress change is determined. Based on whether the formation pressure reaches the critical desorption pressure, mathematical models of reservoir permeability evaluation are established in stages considering multiscale pore space geometric, adsorption layer effect and liquid phase distribution. Then the stress sensitivity evaluation method of normal-pressure shale gas reservoir is put forward. According to the principle of compromise in competition of mesoscience, the normal-pressure shale gas multiscale transport mechanisms with multi-gas transport behaviors involved are clarified considering the influences of transport channel scales, pore wall properties, liquid content and distribution. The research results will not only enrich the theoretical system of normal-pressure shale gas transport, but also be beneficial to the formation damage control during production and production forecast.