川西北地区九龙山气田天然气成因与来源探讨

九龙山气田产层主要为下侏罗统珍珠冲组及上三叠统须家河组须二段，目前对二者气藏的气源还未定论。通过对九龙山气田珍珠冲组和须家河组天然气组分和碳同位素组成的详细分析，结合源岩和储层沥青生物标志化合物开展气源对比，以明确天然气来源。九龙山气田存在浅层须家河组须三段泥页岩和深层的茅口组灰岩、下寒武统泥岩2套优质烃源岩，天然气总体为干气，珍珠冲组与须三段天然气组成特征相似，须二段天然气组成具有须家河组和深层气共同特征。珍珠冲组天然气δ₁₃C₂平均为-26.73‰，与周边文兴场和中坝气田须家河组煤系烃源相似，须二段天然气δ₁₃C₂值在-29.5‰～-30.49‰之间，介于浅层煤成气和深层油型气特征。珍珠冲组气层沥青甾萜烷生物标志化合物也与须三段烃源特征相似，具有高的三环萜烷值和重排甾烷/规则甾烷值，C₂₇/C₂₉值分布在0.93～1.00之间，呈“V”字型特征;须二段气层C₂₇/C₂₉值介于须三段和茅口组、寒武系源岩之间，具有与茅口组相似的三环萜烷低值和重排甾烷/规则甾烷低值特征。综合天然气组分、碳同位素和储层沥青生物标志化合物气源对比分析认为，九龙山气田珍珠冲组天然气主要由浅层须三段腐殖型烃源生烃贡献，须家河组须二段天然气由浅层须三段腐殖型和深层茅口组、下寒武统偏腐泥型烃源混合贡献。

Natural Gas Genesis and Sources in Jiulongshan Gas Field, Northwest Sichuan Basin

Lower Jurassic Zhenzhuchong Formation and the second number of Upper Triassic Xujiahe Formation are two main gas production strata of Jiulongshan Gas Field,however,no conclusion has yet to be reached about gas source for the both strata.Therefore,this contribution makes a detailed analysis about the gas component,carbon isotopic composition,source rocks and reservoir bitumen biomarkers,to clear the gas sources of Zhenzhuchong Formation and the second number of Xujiahe Formation.There are 2 offsets of high quality hydrocarbon sources:the shales of shallow Xujiahe Formation (third number),limestone of deep Maokou Formation and mudstone of Lower Cambrian.In general,gas is dry,and gases from both the Zhenzhuchong Formation and the third number of Xujiahe Formation have similar characteristics,while gases from the second number of Xujiahe Formation have combined characteristics of both shallow and deep gases.δ₁₃C₂value is averaged at -26.73‰ for the gas from Zhenzhuchong Formation，which is similar to the Xujiahe Formation coal source of periphery Wenxingchang and Zhongba Gas Fields.Theδ₁₃C₂ value is from -29.5‰ to -30.49‰ for the gas from the second number of Xujiahe Formation,which demonstrates characteristics of both shallow coal-derived and deep oil-derived gas.Zhenzhuchong Formation has high tricyclic terpane value and rearrangement sterane/steranes value,which is the same as Xujiahe Formation.C₂₇/C₂₉value is from 0.93 to 1.00，like shape “V”.The second number of Xujiahe Formation has similar low tricyclic terpane values and rearrangement sterane/steranes to that in Maokou Formation.Therefore,it is concluded that gases in the Zhenzhuchong Formation is sourced from the third number of Xujiahe Formation,while gases in the second number of Xujiahe Formation are mainly derived from both the third number of Xujiahe Formation and deep Maokou Formation.