【作者】 黄华州；

【导师】 桑树勋； 李国君；

【作者基本信息】 中国矿业大学 ， 矿物学岩石学矿床学， 2010， 博士

【摘要】 基于疏水降压的原位煤层气地面井抽采技术在淮南高瓦斯矿区效果不佳,针对淮南矿区煤层气富集、构造煤发育、长壁多煤层开采等地质与井巷开拓背景,试图探索一种煤矿采动区与煤炭开采相结合的远距离被保护层卸压煤层气地面井抽采地质理论与工程技术。论文以煤储层为切入点,应用光学显微镜观测、电子显微镜观测、地球物理测井、压汞分析、低温液氮吸附、高压等温吸附、渗透率测定等方法手段开展了构造煤的系统观测和储层特性分析,查明了构造煤的地质发育特征和卸压煤层气地面井抽采的储层条件;以卸压煤层气地面井抽采工程跟踪研究、矿井采场岩移监测数据、保护层开采上覆岩层变形与煤层气井孔破坏的相似材料实验模拟和数值模拟为依据,研究了保护层开采引起的被保护层储层改造与渗透性演变规律,奠定了卸压煤层气地面井可采的地质理论基础,并建立了作为煤层气抽采布井、钻井、完井地质依据的远距离卸压煤层气地面井井孔稳定性理论;最终将采场应力下煤储层改造理论与煤层气地面井井孔理论应用于卸压煤层气抽采工程实践,提出了远距离卸压煤层气地面井井位、井身优化设计方案。证实了构造煤储层是卸压煤层气地面井抽采的优质储层。煤体结构的破坏通过增加外生孔的数量,不仅增加了煤孔隙度、总孔容、大孔孔容及中孔孔容,还使微孔孔容及微孔比比表面积大幅增加,使得构造煤煤体破坏程度越高吸附能力越强,储气能力越强。自制加卸载试验仪的实验结果表明构造煤渗透性对于应力的增减较原生结构煤更为敏感,具有更为明显的“加压减流”、“卸压增流”能力,且煤体结构破坏程度越高对应力变化的响应越迅速。原因是应力释放会导致孔隙度的大幅增大、数量较多的高连通性的采动裂隙、卸压松弛裂隙的伴生。揭示了采动影响下远距离被保护层储层渗透性的时空演变规律与改造机理。工作面推进过程中被保护层裂隙发育区及高渗区位于工作面后方的未压实采空区中部,其具有随工作面前移而移动的动态发育规律,且高渗特性保持时间短,限制了地面井抽采的有效抽采时间和产能。采动影响稳定后,裂隙发育区及高渗区位于压实线与四周断裂线限定的环形圈内,构造煤储层得到显著改造,且采动发生后即发育,稳定后仍保持,为卸压煤层气地面井长期高效抽采提供了理论依据。建立了卸压煤层气地面井的井孔稳定性理论。采场应力下上覆岩层移动对井孔的破坏存在平面和层域控制效应,井孔破坏主要表现为剪切破坏和轴向拉压破坏及两者兼有的组合破坏三种力学破坏类型和松散层中下部、岩层软弱结构面、软硬岩层交界、厚软岩层内部四处主要破坏位置。地质及采场工程要素显著影响煤层气井孔稳定性。岩移的大小和速率变化控制了井孔受破坏程度,在平面上采区中线附近受破坏程度大,在层域上靠近开采层的位置受破坏程度大。岩层厚度和岩性组合的综合作用控制了岩层内部井孔破坏位置,上硬下软的岩性组合易发生由离层发育引起的轴向拉压破坏,硬软硬的岩性组合极易在软弱结构面发生剪切破坏,上厚下薄、上软下硬的软岩层中部易发生组合破坏。同时大采高、快推进速度则会加剧以上的各种破坏。以煤储层卸压改造和井孔稳定性理论为依据,探索性地提出了卸压煤层气地面井的采区优化布置和井身优化设计方案,认为采空区压实线与采场四周边界线限定的区域是卸压煤层气抽采布井的最佳位置;提出Ⅰ类井身结构在采高不大于2.0m,推进速度不大于5m/d,松基比不大于1时,Ⅱ类井身结构在采高不大于2.6m,推进速度不大于5m/d,松基比不大于1.8时,具有高稳定性。更多还原

【Abstract】 This study introduces a way to drainge stress relief coalbed methane(CBM) from the distant protected coal seam after the lower protective coal seam mined through surface vertical wells over the longwall panel which is drilled in advance of mining. The compression in the overlying protected coal seam is relieved and gas flow ability is greatly increased because of the relaxation of the overlying strata after the protective coal seam is mined, which make that the wells get high gas production. This study has proved that the stress relief drainage technology through surface vertical wells is scientific in theory through sheared coal reservoir characteristics experiments, physical and numerical simulation tests, moreover, dynamic variation of sheared coal reservoir permeability during the protective coal seam mining and after the protective coal seam mined is summarized to design the well deployment in the area where the high gas flow ability would maintain a long time. Some engineering problems resulted in surface wells stopping producing are analyed too. The position where the wellbore is easily broken is found and some solutions are provided to maintain the wellbore integrity. The design methods of wellbore structure are summarized through engineering practice, and some drilling and completing methods to strengthen the wellbore stability are gave to help the surface well get high drainage efficiency.The results also indicate that reservoir adsorption capacity and gas storage ability is correlated positively with the level of the coal structure destruction. Sheared coal has better gas flow ability than primary coal while the compression is relieved. All these have proved that sheared coal reservoir is convenient for stress relief CBM drainage by surface vertical wells.The permeability of the protected coal seam varied dynamically during the protective coal seam mining and after the protective layer mined. Well developed abscission layer and high permeability area in the protected coal seam locate in the central panel in plane behind the face during mining , it moves with face advancement and has a short life. However, after the lower protective coal seam mined, well developed abscission layer and high permeability area in protected coal seam shifts from the central panel to the zone aound the gob, it may be kept for a long time.The wellbore stability is closely relevant to casing strength, borehole diameters, geological conditions , mining factors of the lower protective coal seam. The wellbore structure of surface wells for stress reilief CBM is destroyed at the beginning of the mining influence because of the axial tension failure and shear failure resulted from overburden movement. Axial tension failure and shear failure to casing is initiated by vertical and horizontal movements of overburden. The extent of the casing failure is different in various position. The failure is serious while wells locate in the central panel in plane and casing is near mined coal seam in vertical direction. The difference of rock layer thickness and the lithology combination have great influence on wellbore stability too. The bigger mining height and greater face advance speed would strengthen all kinds of the above-mentioned failure.Mining fractures and high permeability area are located in zones where lines of compaction and the panel boundary line are determined after its effect has become relatively stable, in this area, the wellbore stability is better than central panel too. So it is the optimum well location for surface vertical wells to drain stress relief CBM.The technology parameters of wellbore structure and their applicalble geological conditions and mining factors are summarized from the engineering practice. And a new kind of wellbore structure is designed to strengthen the wellbore integritybased on the above research results.The drilling and completing technologies are discussed and some suggestions are provided to strengthen the wellbore stability during the lower protective coal seam mining.更多还原