Research on precise quantitative traceability of combined gas extraction in close-distance coal seam group

The combined extraction of gas from close-distance coal seams can be an effective means of preventing and controlling the outburst of coal and gas. It can improve the production efficiency of coal mines and make effective use of coal methane resources. In order to determine the source of the combined extraction of gas in the coal seam group and the proportion of gas extraction in each coal seam, in this work, the combination of carbon isotope measurement, numerical simulation and field layered measurement test are adopted to study the traceability of combined extraction of gas in outburst coal seam group. When the four-layer coal seam is jointly extracted, the gas mixing ratios of the coal seams from top to bottom calculated by the carbon isotope method account for about 23%, 56%, 7% and 13%, respectively. According to the field layered measurement test, the proportion of each coalbed methane in the mixture is about 22%, 55%, 7% and 15% in the top-down four layers of coal seam. In accordance with the numerical simulation study, the top-to-bottom ratio of gas extracted from each coal seam is about 3.4:7.4:1:1.8 when the multi-holes are arranged in parallel to extract the four-layer coal seam. Under the geological conditions of the coal seam in this coal mine, the three research methods all confirm that when the four-layer coal seam is jointly extracted, the amount of gas extracted from the second-layer coal seam is the largest, followed by the amount of gas extracted from the first-layer coal seam, and the amount of gas extracted from the third and fourth-layer coal seams is relatively small. The research offers a theoretical foundation for evaluating the accuracy of measuring the volume of gas extracted from multi-coal seam combined extraction, and provides a new research idea for solving the problem of combined extraction of close-spaced bursting coal seams, which has guiding significance for the accurate measurement of mine gas control.