But it will fail to recognize the gas bearing bed buried deeper by the two methods as its porosity log feature is not obvious, especially when density porosity is lower than neutron porosity.
The porosity and permeability of coal-bearing strata have important influence to the exhaust and mining of coal bed gas, but the production of coal bed gas is precondition 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。
3
Experiments showed decreased porosity of the filter bed along the filtering direction.