Seepage characteristics of gas pool of extra low permeability sandstone under various types of primary water

According to experiments of water-containing cores in the gas pool of sandstone with extra-low permeability in Daniudi gas field of Ordos basin,it is concluded that the wa- ter- containing cores make apparent the starting pressure gradient due to the existence of the occlusion of small pore throat by water film.With the augmentation of water satu- ration,the characteristic curve of gas seepage draws close to the pressure gradient axis gradually.The gas flow rate will increase apparently only after the pressure gradient reaches a certain value.For the same water-containing core,the starting pressure gradient increases with the enhancement of water saturation as an apparent linear relationship;and the lower the permeability of core,the larger the starting pres- sure gradient value at the same water saturation.The tradi- tional binomial deliverability equation is no longer suitable to the analysis on the production of this kind of gas pool.Dur- ing well pattern arrangement,the double maximum propaga- tion distance of the pressure should be used as the reasonable well spacing.