四川盆地陆相天然气地球化学特征及对比

为了系统认识四川盆地陆相天然气地球化学特征及差异，利用天然气组分、碳同位素与轻烃等地球化学资料，对四川盆地不同地区不同层位陆相天然气地球化学特征进行分析及对比，探讨其差异成因。结果表明，四川盆地陆相天然气地球化学特征在横向与纵向均存在较大差异。横向上，川西地区天然气甲烷含量与干燥系数均高于川中地区，川西地区天然气以干气为主，川中地区天然气以湿气为主，地层厚度、埋深及气源岩的不同是造成上述差异的主要原因。不同地区的天然气组分特征参数纵向变化规律也明显不同，川西地区该变化规律主要受烃源岩成熟度与天然气运移分馏影响，而川中地区则主要受烃源岩成熟度及类型的影响。四川盆地陆相天然气以成熟气与高成熟气为主，仅川中地区侏罗系天然气以成熟气为主，川西地区天然气成熟度最高，川中地区与川南地区上三叠统次之，川中地区侏罗系最低，烃源岩埋深与厚度的差异造就了上述成熟度差异。四川盆地陆相天然气以煤型气为主，同时存在一定的油型气，不同地区油型气的含量、分布、成因与来源均存在较大的差异：川西地区仅须二段存在少量油型气，来自马鞍塘组—小塘子组生成的石油裂解；川中地区侏罗系以油型气为主，来自侏罗系干酪根裂解；川南地区须家河组有一定的石油裂解成因油型气，主要来自下伏气藏。四川盆地上三叠统天然气以水溶相与游离相运移，而侏罗系天然气则主要以游离相运移。[JP]

The Geochemical Characteristics and Comparison of the Terrestrial Natural Gas in Sichuan Basin

For the systematic understanding of the geochemical characteristics and differences of the terrestrial natural gas in Sichuan Basin,using the gas components,carbon isotopes,and light hydrocarbons,the characteristics of different strata in different parts of Sichuan Basin and its reasons were analyzed and investigated.The results show that gas geochemical characteristics differ significantly on lateral and longitudinal.On lateral,the methane content and dry coefficient in west Sichuan Basin are greater than those in central Sichuan Basin.The main natural gases in the former and the later are dry and wet gases,respectively.The main reasons of the above-mentioned diversities are the difference in formation thickness,burial depth and source rock.Great difference also exists in the longitudinal change rules of the gas composition.The rule in west Sichuan Basin is mainly affected by the maturity of source rock and the migration fractions of natural gas.However,in central Sichuan Basin,it is affected by the maturity and type of source rock.The gases are mainly mature and highly-mature gases in the study area,and only the central Sichuan Basin′s Jurassic natural gases are mainly mature gases.The maturity of gases is the highest in west Sichuan Basin,second in the Upper Triassic in central and south Sichuan Basin,and the lowest in the Jurassic in central Sichuan Basin.These results are caused by the various formation thicknesses and burial depth.With a little oil type gas,coal type gas is the main terrestrial gas in this area.Differences exist in the content,distribution,cause and source of oil type gas in diverse areas.Only a few oil type gases exist in T₃x₂ of west Sichuan Basin which is from the petroleum cracking of Maantang Formation-Xiaotangzi Formation.Oil type gas,coming from the kerogen cracking of Jurassic,is the dominant natural gas of Jurassic in central Sichuan.Some oil type gas (from the petroleum cracking),mainly deriving from the underlying gas reservoir,exists in Xujiahe Formation of south Sichuan Basin.The migration of the natural gas of the Upper Triassic in Sichuan Basin occurs in water dissolving phase and separate phase while the Jurassic in Sichuan Basin mainly occurs in separate phase.