煤层气U型井煤粉产出机理及影响因素研究

Production Mechanism and Influencing Factors of Coal Powder in U-shape Coalbed Methane Horizontal Well

煤粉产出的控制直接决定煤层气的开采成本与经济效益。针对沁水盆地寿阳区块煤层气U型水平井作业特点,从岩石力学与煤层气地质学角度出发,分析了煤粉来源与产出机理,总结出煤层地质与开采工程扰动对煤粉产出的影响。研究表明:煤粉主要来源于煤层裂缝中游离态的煤粉和因煤体骨架结构破坏产生的煤粉,而引起煤体骨架结构破坏的机理可分为剪切破坏与压实滑移破坏两种;煤粉的产出是多种因素共同作用的结果 ,煤层的地质条件是煤粉产出的内部因素,工程扰动是外部因素。同时提出了适合U型煤层气井的科学的煤粉防控措施:加强煤储层在平面上与垂向的特征研究,采用欠平衡或近平衡钻井工艺尽量避开在易产粉的软煤层进行施工作业;在完井过程中采用玻璃钢管或PE管完井;在排采过程中要保证连续、平稳和合理的降压。

Study on how to control the coal powder production reasonably determines the exploitation cost and economic benefit of the eoalbed methane （CBM） directly.According to operation characteristics of U-shape coalbed methane horizontal wells in Shouyang block of Qinshui Basin,the source and production mechanism of the coal powder were analyzed,and the effect of coal seam geology and engineering disturbance on the coal powder was summed up from the point of rock mechanics and coalbed methane geology.Research shows that the coal powder mainly comes from that in the seam fractures as free state and that produced in the process of coal skeleton structural damage including shear failure and compaction slip failure.Coal powder pro- duction is the result of many factors including internal factors such as geological conditions of the coal seam and external factors such as engineering disturbance.At the same time the suitable scientific measures of pre- vention and control on the coal powder for the area of coalbed methane well were put forward.The study on vertical and areal characteristics of the coal reservoir should be strengthened and underbalanced or approach- ing balance drilling technology will be applied to avoiding operation on the soft seam with easy-produced powder.FRP pipe or PE pipe may be used during the well completion.Continuous,stable and reasonable depressurization should be held in drainage process.