THM耦合作用下低渗透煤层孔裂隙系统渗流特性的时空演化规律研究

It is a technical problem for gas disaster and coalbed methane extraction to extract methane from low permeability coal seams. It is an extremely effective method for extracting methane from low-permeability coalbed reservoir that heating reservoir by injecting superheated vapor (300℃) into coalbed can significantly enhance reservoir permeability and gas desorption. The key for the method is to figure out the fluid flow distribution in the superheated-vapor-injected channel and its surrounding rock. In the program, the methods such as theory analysis, testing and numerical simulation will be taken to carry on the following researches. First, evolution of mechanical properties and permeability of low-permeability coal samples under coupled thermo-hydro-mechanical processes, and the solid and permeability constitutive equation involving temperature. Then morphology of fracking induced fracture, opening and permeability in coal sample during injecting superheated vapor will be studied and the mathematic model involving temperature of fluid flow in fracture will be presented. The distribution of temperature and displacement in coal sample will be obtained by performing the experiment of injecting superheated vapor into large truly triaxial stressed low-permeability coal sample. Lastly, numerical simulation will be taken to study spatio-temporal evolution of fluid flow in pore and fissure system of low permeability coalbed under thermo-hydro-mechanical coupling effect according engineering practice..In the light of the research results, the technical scheme will be proposed for gas production enhancement by injecting superheated vapor into low-permeability coalbed reservoir.

低渗透煤层气开采是目前我国煤层气高效开采及煤矿瓦斯治理的技术难点。采用向低渗透煤层中注过热水蒸汽（300℃）加热煤层的方法可以有效地增加煤层透气性和强化煤层气解吸，是低渗透煤层气大规模高效开采的有效途径。注热通道及其围岩内温度场和渗流场的分布规律是该技术有效实施需解决的关键问题之一。项目采用理论分析、试验研究和数值模拟相结合的方法，拟研究低渗透煤THM耦合作用下力学特性和孔隙渗流特性演化规律，建立考虑温度影响的固体本构模型和孔隙渗流本构方程；利用自制设备研究三轴应力下注热通道裂缝内注过热水蒸汽过程中裂缝形貌特征、张开度和渗流特性的变化，建立含温度变化的裂缝渗流模型；研究真三轴应力下低渗透煤样注过热水蒸汽对流加热过程中温度场和变形场分布规律；通过数值计算，分析低渗透煤层THM耦合作用下孔隙与裂隙系统渗流特性的时空演化规律。为低渗透煤层原位注过热水蒸汽强化煤层气开采主要技术参数确定提供指导。

原位注热能够促进煤层气解吸和增加煤层渗透性，是实现煤层气大规模高效开采的有效技术途径之一。原位注热开采煤层气过程中，受温度（T）-地应力（M）-渗流（H）多场耦合作用，煤层孔裂缝系统渗流特性的时空演化规律是亟需解决的关键科学问题。.项目综合采用物理试验、理论分析和数值模拟相结合方法，研究并获得如下主要成果：.①研究了高温（500℃）三轴应力下煤的力学、渗流特性变化规律，发现500℃内煤的热变形受热膨胀和热解双重作用，经历了缓慢热膨胀、线性热膨胀和压缩变形三个阶段；在300℃及15MPa三轴应力下，煤的破坏仍是脆性破坏，但温度对煤的强度具有弱化作用，弹性模量和峰值强度可用温度的二次函数表示。.②研究了三轴应力下注高温过热水蒸汽过程中单一煤裂缝渗透率变化规律，得出：三轴应力下，长期注400℃过热水蒸汽过程中，当煤样整体温度增加至150℃时，煤单裂缝渗透率提高至初始值的10%以上，且冷却后，裂缝渗透率仍高于注热前，注入高温过热水蒸汽并使裂缝温度达到150℃时，裂缝渗透率得到增强，有利于解吸的煤层气运移；当裂缝内加入支撑剂后，长期注热能够使裂缝渗透率提高1倍多。.③研究了真三轴应力下大尺寸煤样单一裂缝注热过程中的温度分布，得出：裂缝面附近煤体温度受孔裂隙影响，温度升高与蒸汽相变有关，升温过程分为升温-相变恒温-再升温过程，试验获得的等效热传导系数能综合描述热传导和热对流过程，裂缝面煤体孔裂隙越发育，等效热传导系数越大。.④采用大型数值模拟研究了煤层气原位注热开采过程中的渗流传热过程，得出注过热水蒸汽开采煤层气较常规开采产气快，且总产气量提高了近一倍。.研究成果不仅能够促进岩石渗流力学的发展，而且能够有效指导低渗透煤层气原位注热开采工程，具有重要的科学与工程意义。.项目执行期间发表学术论文27篇，其中SCI收录12篇，Ei收录3篇；出版专著1部；获山西省技术发明一等奖1项；申请发明专利4项；培养研究生10人，研究成员中1人获批国家优青项目。