煤层气排采时储层气水状态及其对渗透率的控制作用

During the process of CBM drainage, the state of gas and water in coal reservoirs is in dynamic change with the production of gas and water, resulting in dynamic changes of coal reservoir permeability, which ultimately affects the productivity of CBM well. The dynamic change of coal reservoir permeability, drainage system and productivity of CBM well is closely related to the change of gas and water state. This project will focus on the core scientific problem of the influence of the dynamic change of gas and water state on the permeability during the drainage of CBM, and select the 3# coal seam of Jincheng mining area in Qinshui Basin as the research object. Displacement experiments and low field NMR will be used as the main means. The coal samples with different gas and water saturation and different sequence of saturation will be tested, which can reveal the characteristics difference of gas and water state and permeability with different confining pressures under static conditions. In order to establish an accurate calculation model of permeability based on nuclear magnetic information, the appropriate parameters can be selected according to the experimental results. Combined with permeability test, scanning electron microscope and CT scanning experiments, the change characteristics of pore and fissure of coal before and after displacement can be analyzed, and the dynamic change rule of gas and water state and permeability can be clarified during the process of CBM production. Finally, the linkage change relationship between confining pressure/displacement pressure, gas and water state and permeability can be established, which will provide a theoretical basis and scientific basis for optimizing the drainage system of CBM well and increasing production.

煤层气排采过程中，随气水产出，煤储层内部气、水赋存状态处于动态变化，致使煤储层渗透率动态变化，最终影响煤层气井产能，因此“排采时气水状态变化—煤储层渗透率动态变化—排采制度及气井产能”三者之间息息相关。本项目拟围绕“煤层气排采时储层气、水状态动态变化对渗透率的影响”这一核心科学问题，以沁水盆地晋城矿区3#煤层为研究对象，以驱替实验和低场核磁共振技术为主要手段，对不同气水饱和状态和不同饱和顺序的煤样进行测试分析，揭示静态条件下，煤储层中气、水状态和渗透率在不同围压下的特征差异；依据实验结果，选取合适参数，建立基于核磁信息的渗透率精确计算模型；进而结合煤岩渗透率测试、扫描电镜和CT扫描等实验，分析驱替前后煤体孔裂隙的变化特征，阐明煤层气排采时气、水状态动态变化对渗透率的控制作用，构建围压/驱替压力—气、水状态—渗透率联动变化关系，为煤层气井排采制度优化和增产提产提供理论基础和科学依据。

煤层气排采过程中，随着储层流体的产出，储层内部气、水的赋存状态随之发生动态变化，进而影响到作用于煤基质的有效应力，以及煤基质的吸附膨胀/解吸收缩过程，最终表现为储层渗透率的变化，深刻制约着煤层气井的产能。鉴于此，本项目拟围绕“煤层气排采时，储层气、水状态动态变化对渗透率的影响”这一核心科学问题，以沁水盆地南部寺河矿3#煤为研究对象，在掌握研究区基础地质条件的基础上，以低场核磁共振技术、驱替实验以及覆压孔渗测试为主要手段，对不同气水饱和度的煤样进行了测试分析，揭示了静态条件下，随着围压的改变，煤储层流体分布的变化特征，研究了储层孔-裂隙结构及其非均质性对储层水分布的影响作用，分析了应力与孔-裂隙压缩对水分布的扰动机制，阐明了含水饱和度与应力对渗透率的耦合控制作用；通过设置不同的围压与驱替压力，研究了不同流体赋存特征下煤储层的渗透率变化规律，分析了动态条件下，有效应力与含水饱和度对煤储层孔隙度-渗透率特征的耦合影响；依据实验结果，选取合适的参数，构建了基于核磁信息的渗透率精确计算模型；阐明了煤层气井排采制度对渗透率与产能的控制作用，初步提出了促进煤层气井产能高效释放的方法建议。