A New Coal Permeability Prediction Method Based on Experiment and Dimension Analysis

Summary

This paper aims to investigate the effect of temperature and effectivestress on coal permeability. Through the experiment, we find a reversalphenomenon in which the coal permeability presents different change trends astemperature increases at two sides of the reverse point.

The term "critical effective stress" refers to the effective stress at thereverse point. When effective stress is lower than the critical effectivestress, the outward expansion effect of the coal block caused by grain and gasswell is greater than compaction effect as temperature increases under loweffective stress condition. Therefore, the coal expands primarily outward,which results in fissure opening and permeability increase. When effectivestress is higher than the critical effective stress, high effective stresslimits the coal?s outward expansion. The coal expands inward with increasingtemperature, thus causing fissure closure and permeability decrease.

On the basis of dimension analysis and regression analysis, combined withexperimental data, this paper develops a high-precision semitheoretical coalpermeability model of Qinshui basin in China. Simultaneously, what this paperpresents is a permeability prediction method: measuring coal core permeabilityand 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 coalpermeability prediction.