Abstract
To understand the interlayer change characteristics during coalbed methane(CBM)production from a multilayer superimposed gas-bearing system(MSGS),a large-scale coupled CBM production test device involving multiple fields was developed in the present study and a four-layer superimposed gas-bearing system was simulated.Based on the response characteristics of the deformation and pressure fields during CBM production,the interlayer change characteristics were analyzed.Results show that the reservoir pressure change involves multiple stages,and these changes decrease the pressure in production layers significantly.Changes in other layers are enhanced with proximity to the production layer,and the decrease in reservoir pressure causes shrinking and deformation of the coal body.Owing to the Poisson effect,the adjacent layer deforms by expansion,and this gradually decreases pressure in the layer.A sensitivity coefficient k and a deformation rate X are used to analyze the sensitivity of the other layers to changes in the production layer and the associated damage.The k increases linearly with production time,and both κ and λ increase with proximity to the production layer.The present study demonstrates that for CBM production from an MSGS,the deformation and reservoir pressure evolution data are suitable for determining the production effect characteristics of a coal seam.Targeted protection measures can thus be introduced in adjacent layers to ensure safe and efficient CBM production.
NSTL