Based on the pyrolysis products for the Jurassic low-mature coal under programmed temperature,and chemical and carbon isotopic compositions of natural gas from the Kuqa Depression, the genetic origin of natural gas was determined,and then a gas filling model was established,in combination with the geological background of the Kuqa Depression.The active energy of CH_4,C_2H_6 and C_3H_8 was gotten after the data of pyrolysis gas products under different heating rates（2℃/h and 20℃/h）were fitted by the Gas Oil Ratio（GOR）Isotope Model soft.When the frequency factor（Af）was chosen as 1×10^（14）,the active energy of CH_4,C_2H_6 and C_3H_8 was 58 kcal/mol,57 kcal/mol and 54 kcal/ mol,respectively.The distributive ranges of theδ^（13）C_1,δ^（13）C_2 andδ^（13）C_3 values for the pyrolysis gas products are-35.9‰to-30.7‰,-26.2‰to-21.3‰and-26.4‰to-22.7‰,respectively.All of the natural gases from the Kuqa Depression are dominated by hydrocarbon gases,with the high gas dryness（C_1/C_（1-4））at the middle and northern parts of the depression and the low values at both east and west sides and the southern part.The carbon isotopes of methane and its homologs as a typical coal-type gas are enriched in ^（13）C,and the distributive range of theδ^（13）C_1,δ^（13）C_2 andδ^（13）C_3 value is-32‰to -38‰,-22‰to-24‰and-20‰to-22‰,respectively,with the carbon isotopes of gaseous alkanes being less negative with the carbon number.With the ethane being enriched in ^（13）C the increasing tendency of the geological reserve of natural gas in the Kuqa Depression is observed.This observed change is consistent with the results of pyrolysate gas yield of coal as a potential gas source in the Kuqa Depression,suggesting natural gas was thermally derived from the humic organic matters and the carbon isotopes of gaseous alkanes would coarsely predict the geological reserve of gas in the Kuqa Depression.Through the simulation of kinetic processes of gas generation for the Jurassi
LIU QuanyouZHANG TongweiJIN ZhijunQIN ShengfeiTANG YongchunLIU Wenhui
