Implications of Geological Conditions on Gas Contents: A Case Study in the Pingdingshan Coalfield

Abstract

Coalbed methane occurrence and its geological control factors are important for coal and gas co-mining. In recent years, more than 50% of the outburst accidents occurred near the faults and the thickening strips in Chinese mines. Therefore, studying the gas occurrence and its controlling factors is vital to prevent gas disasters in outburst mines with complex geology. In this paper, the distributions of faults, coal thickness, and gas content were characterized and analyzed based on fractal theory and geostatistics. Then, finer coal thickness inverted by the cross-layer boreholes for gas extraction was analyzed at a single working face. The geological control characteristics of gas contents were finally studied. The results show that coal thickness, burial depth, and fault complexity are the geological factors controlling gas contents from a regional to local scale. The sedimentary environment determines the regional coal thickness distribution and even stratification, which leads to higher gas content in the eastern thick-coal region than in the west. And the gas content varies linearly with burial depth in the same geological zonation. The fault fractal dimension is a quantitative representation of fault complexity. The dense distribution of minor faults is why the sizable fractal dimension in the local region is crucial in controlling the uneven enrichment of gas content. Therefore, more refined geological detection and characterization is the way to gas precision control in the future.