徐深1井深层天然气地球化学特征与各类气源岩的贡献

徐深1井4个井段天然气甲烷组分都占烃类含量的97%以上,演化程度随着埋深而增加。随着演化程度加深,链烷烃脱甲基、环烷烃开环作用、芳构化作用和烷基化程度不断提高。营城组天然气甲烷碳同位素值比乙烷的重,碳同位素值都有反序特征;火石岭组天然气甲烷碳同位素值为-29.20‰,乙烷碳同位素值未检测到。徐深1井营城组具有腐殖型特征,处于高-过成熟演化阶段;火石岭组则具有腐泥型特征,为高-过成熟天然气。利用烃源岩及天然气烃指纹色谱技术和模拟计算软件建立了源岩贡献比例计算模板。经模板计算,徐深1井营城组天然气来自沙河子组烃源岩的占54%以上;火石岭组天然气来自火石岭组烃源岩的占50%,来自沙河子组烃源岩的占43.08%。营城组和石炭—二叠系烃源岩对营城组和火石岭组天然气的贡献均较小。

Geochemical features of natural gas in deep reservoirs in Xushen 1 well and Contribution of various source rocks

The methane content accounts for over 97% of natural gas compositions in the 4 pay zones in Xushen 1 well.The degree of hydrocarbon evolution increases with depth,which is accompanied by demethylation of alkanes,ring opening of cycloalkanes,aromatization and heightening alkylating degree.For the gas in Yingcheng Fm,the carbon isotope values of methane are heavier than that of ethane.For the gas in Huoshiling Fm,the carbon isotope value of methane is-29.20‰,but the carbon isotope value of ethane is not detectable.The source rocks in Yingcheng Fm in Xushen 1 well are characterized by their humic-type organic matters,and is in high-to over-mature evolution stage;While the source rocks in Huoshiling Fm are characterized by their sapropelic-type organic matters,and generate high-to over-mature natural gas.A quantitative model for natural gas generation is developed by using the hydrocarbon fingerprint chromatograms of source rocks and natural gas and mathematic simulation software.Calculation results show that the source rocks in Shahezi Fm would have contributed over 54% of gas to the reservoir in Yingcheng Fm in Xushen 1 well,while the source rocks in Huoshiling and Shahezi Fms would have contributed 50% and 43.08% of gas to the reservoir in Huoshiling Fm,respectively.Only very little gas in the Yingcheng and Huoshiling Fms have been derived from the Yingcheng Fm and Permo-Carboniferous source rocks.