The porosity and permeability of coal-bearing strata have important influen ce to the exhaust and mining of coal bed gas , but the production of coal bed gas is prec ondition of its richen.

• 煤系地层孔隙性和渗透率对煤层气的抽放、排采具有重要影响,但煤层气的生成却是其富集的先决条件。