Reliable estimation of gas reserves in coalbed methane (CBM) reservoirs requires accuratedetermination of adsorption isotherms relating the ability of coal to adsorb gas in the presence ofwater.Gas diffuses through the water,enters the matrix structure,and then adsorbs on the coalsurface.This process is relatively slow and therefore,the time and effort required for constructingequilibrium isotherms are usually very demanding.This paper presents a rapid approach fordetermining the equilibrium gas isotherms by means of the measurements conducted with thecoal samples taken from the wet coalbed methane (CBM) reservoirs containing a system of gas,water,and coal.A new data interpretation method is developed in order to reduce the timerequired to construct the equilibrium gas isotherms using the experimental data obtained bymeans of non-equilibrium measurements.This is accomplished with a theoretical approach,implementing non-equilibrium thermodynamics of gas and water adsorption on the coal surface,using well-established isotherms along with unsteady-state description of mass transfer betweenthe cleat and matrix of the coal.The applicability of this approach is verified by analyzing a varietyof non-equilibrium experimental data.
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