Summary
This paper aims to investigate the effect of temperature and effective stress on coal permeability. Through the experiment, we find a reversal phenomenon in which the coal permeability presents different change trends as temperature increases at two sides of the reverse point.
The term “critical effective stress” refers to the effective stress at the reverse point. When effective stress is lower than the critical effective stress, the outward expansion effect of the coal block caused by grain and gas swell is greater than compaction effect as temperature increases under low effective stress condition. Therefore, the coal expands primarily outward, which results in fissure opening and permeability increase. When effective stress is higher than the critical effective stress, high effective stress limits the coal's outward expansion. The coal expands inward with increasing temperature, thus causing fissure closure and permeability decrease.
On the basis of dimension analysis and regression analysis, combined with experimental data, this paper develops a high-precision semitheoretical coal permeability model of Qinshui basin in China. Simultaneously, what this paper presents is a permeability prediction method: measuring coal core permeability and performing dimension analysis and regression analysis. With this work done, we can establish a similar permeability model suitable for other target zones. Thus, the analytical method presented in this paper provides a basis for coal permeability prediction.
Model development and analysis of coal permeability based on the equivalent characteristics of dual-porosity structure
