Origin and Geochemistry of Natural Gas in Kuqa Depression, Tarim Basin

Geochemical characteristics of natural gas in Kuqa depression of Tarim basin are studied. The maturity and source of gas in the depression is discussed by using the result of carbon isotope kinetics. The gas in Kuqa depression, containing wet gas, condensate and dry gas, appears the trends of both methane content and dryness coefficient decreases from west to east and from north to south. It belongs to coal-formed gas and originates from Mesozoic source rocks. Its maturity in different structural belts is differentiated with Ro ranging from 0.7% to over 2%. The Ro of gas from Kela-2 gas field ranges from 1.3% to 2.5%. It is considered from the comprehensive data analyses that the major source rocks in Kuqa depression should be Jurassic coal-bearing source rocks, while Triassic source rocks make the second contribution to the gas pool in it.