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.