煤层气其实是吸附气

Coalbed methane is adsorption gas underground

煤层气开发正迅速发展,但学术界对煤层气的赋存状态问题仍存有争议。针对此问题,主要从煤层气的赋存机理和开采机理进行了研究。结果表明:①泥岩烃源岩的有机质含量低,吸附的甲烷数量少,基本上不具有开采价值;煤岩的有机质含量高,有机质吸附的甲烷数量多,具有开采价值。②煤岩的有机质极性弱,易于吸附极性弱的甲烷分子,而极性较强的矿物质则倾向于吸附水分子。③煤岩由基质岩块和裂缝组成,是裂缝性泥岩,由煤岩基质生成的甲烷自由气都运移到裂缝并散失掉了,只有吸附气保存了下来。④煤层气需要排水降压,使地层水脱气、吸附气解吸并形成自由气后运移至裂缝中才能被开采出来。⑤煤层气开采存在临界产气压力,并且在开采过程中不存在扩散现象。

Coalbed methane development is growing fast. However the occurrence state of coalbed methane is still in query, for which a study was conducted in this paper. Source rock of mudstone has a small amount of organic material, which can only absorb quite small amount of methane recoverable without economic value. However coal has a large amount of organic material, which can absorb a large amount of methane recoverable with economic value. Organic material of coal rock is polarized weak on molecules, is likely to adsorb methane molecules with weak polarization. The strongly polarized minerals in coal rock are likely to adsorb water molecules with strong polarization. Coal rock consists of matrix block and fractures, which can be called fractured mudstone. The methane in free gas generated in matrix migrated to fractures and was lost away, and finally only adsorption gas was stored and kept. It needs to produce water and decrease formation pressure to develop coalbed methane. Pressure drawdown can degas the formation water, and desorb adsorption methane, and generate free gas. Then free gas migrates to fractures and will be produced to surface. There is critical production pressure for coalbed methane development. The process of coalbed methane production does not have diffusion phenomena.