Thedifference of gas production law between initial stage and later stage of shalegas well is essentially attributed to the difference of occurrence

migrationand production mechanisms of adsorbed gas and porous medium-confined gas inthree dimensional stress states. In order to reveal the influence of averageeffective stress on the production law of porous medium-confined gas in theinitial stage and adsorbed gas in the later stage of coal shale gas wellproduction from a micro perspective

and to simulate the whole processes ofcoal shale gas adsorption and desorption in situ stress state

nuclear magneticresonance spectrums method was applied to the whole process of experimental research onisothermal adsorption and desorption of the same coal shale sample situ stressstate from Dongbaowei Mine #36 seam in Shuangyashan basin. The averageeffective stress was taken as the comprehensive measurement index of coalshale

and the amplitude integral of nuclear magnetic resonance spectrum was used as thecharacterization index of micro adsorbed gas and porous medium-confined gas.The relationships between micro adsorbed and porous medium-confined gas contentand average effective stress of coal shale in adsorption and desorption werequantitatively studied. The relationships between the hysteresis coefficient ofmicro adsorbed and porous medium-confined gas and the average effective stresswere studied quantitatively. The influence of average effective stress on theoccurrence and output of micro adsorbed and porous medium-confined gas in coalshale was clarified by multi factor linear regression. The experimental resultsshowed that

the adsorbed gas content of coal shale and average effectivestress could be fitted by Dubinin-Radushkevich function model in the adsorptionand they could be fitted by Weibull function model in the desorption. Theporous medium-confined gas content of coal shale and average effective stresscould be fitted by linear function model. The hysteresis coefficient of microadsorbed gas and the average effective stress accorded with the logarithmicfunction model. However

the decrease of average effective stress had littleeffect on the hysteresis coefficient of micro free gas

and the hysteresiscoefficient of porous medium-confined gas was approximately 41.53%. The porepressure of reservoir and vertical stress of overlying strata were the maincontrol stress factors of micro adsorption and desorption

respectively. Theoccurrence and output of free gas were mainly related to the stress ofsurrounding rock.