Statistic analysis on macro distribution law of geostress field in coalbed methane reservoir

Based on the site measured data of the in-situ geostress from 232 hierarchy coalbed methane wells in East Hubei, Qinnan, Western Guizhou-Eastern Yunnan and Huainan Regions, in references to the Hoek-Brown analysis method, the macro geostress distribution law of the coalbed methane reservoir was systematically analyzed and the different stress parameters with the depth varied curve were regressively established in order to provide the references to the judgment of the stress status in the deep coal reservoir and the selection of the rock parameters. The results showed that the coal reservoir in China was in a medium - high stress area, the type of the stress field was in an inhomogeneous distribution,σH>σv>σh type and σv>σH>σh type would be 94% mainly and the σH>σh>σv type would be less concentrated in the shallow depth.The lateral pressure coefficients k of the coal reservoir was less than the average value of Hoek-Brown and 88% of the site measured data would be lower than the domestic average line.The σH/σv and k value varied with the depth both could be explained with the hyperbola shape and the integration would be “dispersion in shallow and convergence in deep depth”.The horizontal principal stress difference would have a certain linear positive correlation with the depth. While the variation of the σH/σh was not high, would be between 1.015～1.915 mainly and the average would be 1.47.The research results can provide reference for the judgment of the stress state of deep coal reservoirs and the selection of rock parameters.