Abstract: Shale gas tends to exist in the forms of adsorbed and free gas in reservoirs.Accurate determination of the ratio of adsorbed-free gas is of great significance to evaluating shale gas content and making reasonable plan for shale gas exploitation.At present,there are hardly any fine evaluation of the adsorbed-free gas content,and the influential factors and mutual conversion pattern of adsorbed-free shale gas are rarely known in the Wufeng-Longmaxi Formations,Fuling area.Hence,based on the analyses of influential factors on adsorbed-free gas,we built a model to quantitatively calculate the maximum adsorption capacity according to the mass of shale,and chose a preferred micropore filling model to characterize the absolute adsorption capacity of shale,in an effort to measure the real adsorbed and free gas contents of shale and figure out the ratio of adsorbed-free gas.In addition,the effect of factors including temperature,TOC,water saturation and porosity,on the mutual conversion of adsorbed-free gas,is also under discussion.The results show that,the adsorbed gas content tends to increase from shallower to deeper layers of the Wufeng-Longmaxi Formations,but the absolute adsorbed gas content of the shale stays steady as the depth further increasing.The average ratio of the adsorbed-free gas is about 34% in the shale studied.In comparing the effects of individual factors on the mutual conversion at a depth of 2 000 m to 3 500 m,we found that the effect of porosity and TOC is the most significant,followed by the water saturation,and that of pressure coefficient variation is the least.

Key words: adsorbed-free gas mutual conversion, quantitative evaluation, Wufeng-Longmaxi Formations, shale gas, Fuling area