摘要
Three types of natural gases,including coal-derived gas,oil-derived gas and biogenic gas have been found in the Liaodong Bay.All of the natural gases in the main gas fields of the Liaodong Bay are wet gas except those in JZ31-6 which are dry biogenic gas.The natural gas mainly distributes in the northern part of the Liaodong Bay with only a small part in the southern part.In the deep,it mainly distributes in the Shahejie Formation with little in the lower Dongying Formation and the Neogene.The distribution characteristics of the natural gas is controlled by the types and thermal maturity of the organic matters,the thickness of the cap rocks and the formation mechanisms of the overpressure.The organic matter in the northern part are typeⅡ2-prone which mainly generates natural gas with a higher maturity while those in the northern part are typeⅡ1-prone which mainly generates oil with a lower maturity.The thickness of the cap rocks in the 3rd member of the Dongying Formation(E3d3) decreases from the north to the south.The overpressure which evolves in the 3rd member of the Dongying Formation(E3d3) is caused by the uncompaction,providing a good condition for the gas preservation in cooperation with the huge-thick cap rocks,while the overpressure which evolves in the 3rd member of the Shahejie Formation(E3s3) is caused by the expansion of the hydrocarbon,providing a strong power for the natural gas which migrates from the sag to the Liaoxi Salient.