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Abstract In order to accurately determine the stress of coal matrix in different coal reservoir properties and different surrounding rock stress conditions，the stress mathematical model of coal matrix by fully considering the coupling effects among the solid，liquid and gas in reservoir was established. Considering the compositions of internal material of the coal reservoir，the coal reservoir geometry concept model was established based on the spherical pore structure. Combined with the elastoplastic mechanics theory，the mathematical model about the effective stress coefficient was gained. Considering the damage evolution processes of coal total stress and pore stress with damage mechanics theory，the effective stress mathematical model of coal reservoir matrix was established. Taking the original reservoir parameters in Fanzhuang block for example，the effective stress changing laws were gained in different reservoir parameters：the effective stress is larger influenced by porosity and gas saturation. When other conditions are the same，with increasing of porosity or gas saturation，the stress of the coal matrix is exponentially decreasing. However，the influence of porosity is more intense than that of the gas saturation，the exponential relation curve between effective stress and gas saturation is more obvious than the porosity. The distributions of pores size and stresses are different. Under the same porosity conditions，with the increase of proportion of the biggest holes，it is logarithmic reduction. The effective stress is linearly reduced with water saturation increases.
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Received: 24 December 2012
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2014, Vol. 33 
