The dryness coefficient is widely used in the studies on the geochemical characteristics

genetic types and accumulation of coal-derived gas

but only a few of them have addressed the factors affecting the dryness coefficient of coal-derived gas.The major coal-derived gas fields of the Upper Paleozoic reservoir in northern Ordos Basin

such as Dongsheng (Hangjinqi)

Daniudi and Sulige

are chosen.Based on the measured and collected data of chemical components

lateral and vertical distribution characteristics of dryness coefficient of coal-derived gas are analyzed

and a two-stage vertical distribution pattern is established.The main controlling geological factors are discussed within the context of regional geological background.The results indicate that ① the dryness coefficient of the Upper Paleozoic coal-derived gas decreases from the center to the margin of the basin

and it displays a two-stage vertical distribution pattern in which the dryness coefficient firstly increases and then decreases from bottom to top.② The dryness coefficient of coal-derived gas is influenced by maturity

geochromatograph effect and leakage effect.③ The maturity of the Upper Paleozoic source rocks determines the regional distribution characteristics of the dryness coefficient.The main controlling factors affecting the "two-stage" vertical distribution of the dryness coefficient are different in the different depth.The source layer and geochromatograph effect the lower and upper reservoirs

respectively.The dryness coefficient is also affected by leakage effect in the areas with poor preservation conditions.