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.

The geological factors affecting gas content and permeability of coal seam and reservoir characteristics in Wenjiaba block, Guizhou province

“…The buried depth of the coal seam in Guizhou mountainous area is calculated by the average elevation of the coal seam outcrop minus the peak of the coal seam. The buried depth of coal seam in the study area is mainly distributed in 200–800 m, which is the most favorable buried depth range for commercial development of coalbed methane 34 . From the contour map of the buried depth of No.16, No.27 and No.30 coal seams (Fig.…”

Experimental Study on the Determinant Factors and Energy Criterion of Coal and Gas Outbursts

“…Recently, outburst accidents have often occur, mainly in coal mining countries such as China, Russia, Poland, and Australia . With the deep mining of coal mines, the frequency of occurrences of various mining geological disasters has also increased greatly. , Under deep mining conditions, which involves high temperature, high in situ stress, high gas pressure, high-pressure karst water, and severe rock fragmentation, as a consequence, the possibility of outburst accidents also further increases. − Since the first global outburst accident, many hypotheses and theories related to outbursts have been proposed by some scholars. , Gas pressure, in situ stress, and coal strength have been identified as the dominant factors that combined to create outbursts and contribute to the energy required to pulverize and remove lots of crushed coal from the working face. − Furthermore, the outburst mechanism has been fully explained and analyzed by the hypothesis of comprehensive action of outbursts in detail, and the hypothesis of comprehensive action of outbursts has also been recognized by most researchers.…”

“… 2 With the deep mining of coal mines, the frequency of occurrences of various mining geological disasters has also increased greatly. 3 , 4 Under deep mining conditions, which involves high temperature, high in situ stress, high gas pressure, high-pressure karst water, and severe rock fragmentation, as a consequence, the possibility of outburst accidents also further increases. 5 − 8 Since the first global outburst accident, many hypotheses and theories related to outbursts have been proposed by some scholars.…”