Analysis and prediction of gas recovery from abandoned underground coal mines in China

Abstract

Mine closures will be especially widespread in eastern China. However, Because of relatively high residual coal-bed methane content, the abandoned coal mine methane (ACMM) reserves of China are huge, and from a greenhouse gas control perspective it is preferable that they be developed and utilized, rather than allowed to vent to the atmosphere. The exploitation and development of ACMM in China is still in its infancy, with theory and practice undergoing rapid development. Four factors are particularly influential on design of ACMM recovery strategies. The first factor is what may be termed the "enrichment space", which reflects the final state of the strata after completion of longwall extraction and subsequent strata settlement, and is here defined as the region between the outer, limit of stress relief and the limit of the extracted panels. Quantitative analysis of the components of gas mixtures recovered from the enrichment space can be tracked using stable carbon isotope techniques. The second factor is the permeability field surrounding the abandoned mine voids. The thick mudstones that commonly overlie the coal seams serve to confine the water and gas within the enrichment space and old mine voids. The geometry of these confining layers can be confirmed by seismic reflection or other geophysical methods, which can reveal the extent of the zone affected by fracture development. On this basis, models of methane movement in abandoned mines can be constrained, allowing valuable predictions of availability of ACMM resources under different mining and post-closure drainage conditions.