构造煤中N2驱替CH4纳-微孔裂隙演化特征与发生条件联动效应

It is the key to improve the effectiveness of construction and reduce blindness of construction to find out the evolution characteristics of nanometer pores and micron fractures and the connected effects with the changing of injection critical conditions..The project intends to different deformation degree tectonic coal in Lu’an, He’bi and Ping ding-shan mining area as the research objects, the nanometer pore structure (scanning electron microscope, mercury injection, Nitrogen/carbon dioxide adsorption method) and micro fracture structure (optical microscope, CT scan, NMR) in tectonic coal in the original states were observed and tested. Based on adsorption potential theory, surface free energy theory, fractal theory and percolation theory, the critical values about adsorption pores, diffusion pores and seepage fractures were determined, the combined types were classified. By using of the technologies and methods that the testing of the oxygen groups and main elements in tectonic coal, construction of molecular structure model, experiment of deformation and permeability in the isothermal adsorption and displacement process, the simulation of the changing about pore sizes, mathematical models about construction of fractures deformation, the evolution characteristics about nanometer pores and micro fractures in the process of nitrogen displacing methane in different deformation degree of the tectonic coal were identified. The mathematical models of the pore sizes of adsorption pore-gas pressure - gas content and gas migration resistance were established, the linkage changing mechanism of the critical entry conditions and the entry amount of nitrogen into the nanometer pores caused by the diameters changing of the nanometer pores and micro fractures is revealed. Which can provides the theory basis for the effective injecting nitrogen and displacement amounts of the methane in the tectonic coal reservoir.

查明氮气注入构造煤储层驱替甲烷气引起的纳-微孔裂隙演化特征及其与注入临界条件变化的联动效应是提高其施工有效性、减少施工盲目性的关键。.本项目拟以潞安、鹤壁和平顶山等矿区的构造煤为研究对象，进行原始状态下构造煤中纳米级孔隙结构（扫描电镜、压汞、N2/CO2吸附法），微米级裂隙结构（光学显微镜、CT扫描、核磁共振）观测，基于吸附势、表面自由能、分形、渗流等理论，确定吸附孔、扩散孔、渗流裂隙的临界值并划分其组合类型；采用构造煤含氧官能团及主要元素测试、分子结构模型构建、等温吸附-驱替过程变形量-渗透率测试、孔径变化模拟、微裂隙变形数学建模等技术与方法，查明构造煤中N2驱替CH4过程中纳-微孔裂隙结构演化特征；构建吸附孔径-气压-含气量和气体运移毛管阻力的数学模型，揭示出纳-微孔径变化引起的氮气进入纳米孔临界条件和进入量的联动变化机制，以期为构造煤中氮气伴注的有效性、甲烷驱替量等研究提供理论依据。

为了查明构造煤中氮气驱替甲烷过程不同纳-微孔裂隙组合类型下纳米孔隙-微米裂隙的转化特征及氮气进入纳米孔隙条件，为现场构造煤中氮气注入参数优化、注入方式选择提供理论依据。本项目以山西潞安、鹤壁和平顶山矿区的构造煤为研究对象，进行了压汞、液氮吸附、光学显微镜、扫描电子显微镜、核磁共振等实验，结合核磁共振T2谱和分形理论，确定出扩散孔、渗流孔-微裂隙的临界值；建立了孔-裂隙综合评价参数体系，划分了孔-裂隙组合类型。进行了元素分析、X射线光电子能谱（XPS）、傅立叶变换红外光谱（FTIR）和核磁共振碳谱（13C-NMR）等实验，并应用ACD/CNMR predictor 软件、MS( materials studio)软件，优化构建出煤的立体分子结构模型，模拟得出了CH4、N2及CH4/N2混合气的吸附量随压力的变化特征。进行了煤吸附甲烷/氮气以及氮气驱替甲烷引起煤基质变形、渗透率变化实验，构建了相应的数理模型，得出了其变化规律。构建了氮气注入CH4进入的临界尺寸及进入量的数学模型，并模拟得出了关键地质储层参数和注入参数下对采收率的影响。.结果表明：（1）扩散孔和渗流-微裂隙的临界值分别为72 nm和2.5 ms。研究煤样可划分为高扩散高渗流连通较差型、低扩散高渗流连通较好型、低扩散低渗流连通较好型等三种组合类型。.（2）随着煤阶升高，煤中芳香烃结构从“以苯和萘为主”逐渐变为“以萘和蒽为主、四环和五环芳香化合物结构芘为辅”的形式。.（3）当50%CH4+50%N2混合吸附时，PDS煤、HB煤、CP煤达到最佳驱替效果时的压力分别为3MPa、4.5MPa和6MPa。吸附孔结构中芳香环结构占比越高，驱替压力越高。.（4）煤岩吸附甲烷、氮气、氮气驱替甲烷引起的基质变形量均符合Langmuir方程形式。并表现出：低压时渗透率变化较快；随着压力升高，渗透率变化变慢。.（5）注入氮气后，氮气的分压作用和基质收缩作用有利于甲烷气体解吸产出。其他条件相同时，纳米级孔隙越多，越不利于注气驱替。采用闷压、循环方式并选择产气超过1年的井进行注入，驱替效果相对较好。