Accumulation Mechanism Types And Spectrum Of Natural Gas In The E₂s₃, Southern Eastern Sag Of Liaohe Depression

The 3^rd member of Shahejie Formation（E₂s₃） in the south part of eastern sag of Liaohe depression has complex condition for gas accumulations. But the long-term exploration goal is conventional natural gas, leading few gas accumulations discovery. It is necessary and urgent to carry out research on the types of gas accumulations and distribution. In this paper, systematic analysis on the geological conditions of natural gas in E₂s₃ are employed,the type of gas accumulation mechanism are studied with the well, drilling ,logging and other test results, natural gas distribution sequence and modeling are established through natural gas characterization and main controlling factors analysis, which has significance to guide the gas exploration in E₂s₃ of southern eastern sag of Liaohe Depression.According to the mechanism of gas accumulation and research data, two types of source rocks （coal layer and shale）, three kinds of reservoirs （sandstone, shale and coal） and various combination of source-reservoir-seal possess various geological conditions for multi-types natural gas in E₂s₃ of southern eastern sag. Gas types in E₂s₃ include CBM, shale gas, source-contacting gas and natural gas. The total hydrocarbon abnormal in gas logging curve is the direct evidence for CBM, shale gas and source-contacting gas exist in coal, shale and the bottom of tight sand. Studies suggest that shale gas, source-contacting gas and conventional gas are main distributed in E₂s₃^1-2, CBM, shale gas, source-contacting gas and conventional gas are main distributed in E₂s₃³.CBM is mainly distributed vertically between 2100m-3600m.Taoyuan, Huangjindai, Dapingfang and Rongxingtun area are the CBM favorable area,because of the moderate coal depth,thickness,high thermal metamorphism,high adsorbed gas content and higher abnormal of gas logging total hydrocarbon. Shale gas is mainly distributed between 3000m-3600m, Jiazhangsi sag and Erjiegou sag and Rongxingtun, Dapingfang-Taoyuan-Huangyure are the shale gas favorable distribution area, because of its thickness,high TOC,moderate thermal evolution, high hydrocarbon generation potential and higher abnormal of gas logging total hydrocarbon. Source-contacting gas is mainly distributed between 3000m-3300m, the edge of Jiazhangsi sag and Erjiegou sag near the hydrocarbon-generation center, tight reservoir rock directly with the source rock, is area of source-contacting gas favorable distribution. Conventional natural gas accumulations are controlled by hydrocarbon- generation center, favorable structural positions, favorable sedimentary facies and the regional seal, Dapingfang-Hongxing,Rongxingtun are the conventional natural gas distribution favorable areas in E₂s₃³.All types of gas reservoirs in E₂s₃ are associated with each other and gradual transit from one type to another. In that way, all types of gas reservoirs compose the natural gas accumulation spectrum in the E₂s₃ of southern eastern sag. That is, vertically, from the bottom to up form shale gas, CBM, source-contacting gas, conventional gas spectrum in the E₂s₃³.Planely, from sag to surrounding form shale gas, source-contacting, CBM, gas-conventional gas spectrum in the E₂s₃³,horizonly, from sag to slope zone form shale gas, source-contacting gas, conventional gas spectrum in the E₂s₃^1-2, from sag to slope zone form shale gas, source-contacting gas, CBM, conventional gas spectrum in the E₂s₃³.