Study on physical simulation test method of coalbed methane production in superimposed gas-bearing system

In order to study the spatio-temporal dynamic evolution characteristics of reservoir parameters and productionduring the coalbed methane (CBM)production of multi-superimposed gas system in the eastern Yunnan and western Guizhou area, the CBM production system has been reformed and upgraded for the special CBM reservoir-forming characteristics and existing testing equipments. The components of the coal-bed methane mining system consists of drainage pipes, gas-water separators, production pipelines, and other accessories. A set of physical simulation test methods for CBM production was establishedfor the selection of aggregate materials,specimen preparation and coalbed methane mining. Finally, the advantages of the test system and method, the future improvement directions and the applicable conditions were summarized.In order to verify the effect of physical simulation test method, a vertical well was used as an example to carry out a coal-bed methane mining experiment with a superimposed gas-bearing system, and the dynamic evolution law of gas pressure, coal seam temperature, coal seam deformation, production and other parameters in the process of coalbed methane mining in 4 coal seams was studied.The experimental resultsshow thatthe gas pressure is approximately elliptical with the wellbore as the center. The closer to the wellhole,the lower the gas pressure, and vice versa. The gas migration speed gradually decreases from near well section to far well section.The temperature decreases from the central axis of the wellbore to the boundary. The closer to the wellbore, the greater the temperature drop, and vice versaThe final volumetric strains of coal seams 1 to 4 at 360 min is 0.067%, 0.109%, 0.117% and 0.154% respectively, and the larger the initial gas pressure of the coal seam, the larger the final deformation. The lower the initial reservoir pressure is, the earlier the volumetric strain growth rate slows down.The instantaneous production curves show a single peak curve type which quickly reaches the peak and drops sharply in the early stage.The research results verify the reliability of the physical simulation test method for superimposed gas-bearing coalbed methane mining, and can provide a reference for on-site coalbed methane mining.