塔里木盆地塔深1井寒武系油气地球化学特征

塔深1井是中国及亚洲陆上最深的探井。在埋深8400m左右、温度160℃、压力80MPa环境下的上寒武统白云岩溶洞储集体中发现了褐黄色的液态烃。研究表明,井深6800~7358m的下奥陶统—上寒武统气样的烃类气体含量为97%,干燥系数为0.97,甲烷碳同位素平均值为-37.9‰,对应的气源岩R_o为1.65%~1.91%,属于典型高演化油型干气,天然气轻烃指纹分析表明与塔河天然气具有相似的母质来源;塔深1井(8406.4~8407.37m)液态烃的正构烷烃齐全,OEP为1.029,C₂₁-/C₂₁+为0.49~1.46,Pr/Ph为0.762~0.991,具有植烷优势,反映了还原—强还原环境的海相腐泥型烃源岩;从表征原油成熟度变化的Pr/nC₁₇,Pr/nC₁₈及芳烃甲基菲指数等分析,与塔河油田奥陶系原油有较大区别,与来自中下寒武统烃源岩的塔东2井、T904井原油相似,其族组分碳同位素δ13C分布于-29.13‰~-25.84‰,具C₂₇>C₂₈<29甾烷特征,初步认为其来自于中下寒武统烃源岩,而高地层压力可能是其保存的重要原因。 

GEOCHEMICAL CHARACTERISTICS OF THE CAMBRIAN OIL AND GAS IN WELL TASHEN 1, THE TARIM BASIN

The Well Tashen 1 in Tarim Basin is the deepest subaerial well both in China and in Asia.The brown liquid hydrocarbon had been first discovered in the Upper Cambrian dolomite pore and cave with the formation temperature being 160℃,the formation pressure being 80 MPa and the buried depth being 8 400 m.The systematic geochemical analysis on the gas and liquid hydrocarbon from the Lower Ordovician to the Upper Cambrian in Well Tashen 1 shows that the content of hydrocarbon gas is 97 percent,the dryness factor of the gas is 0.97 and the average carbon isotope of CH₄ is -37.9‰.The R_o of the correspondent source rock is from 1.65% to 1.91%,which is characteristic of typical oily dry gas with high thermal maturity.Various biomarkers and distribution of isotope of petroleum family composition in the saturated fraction from extracts of two samples in Well Tashen 1 indicate that the distribution of n-alkanes is complete(from nC₁₃ to nC₃₈ with the C₂₃ being dominant),the OEP is 1.029,the C₂₁-/C₂₁+ is from 0.49 to 1.46 and the ratio of Pr to Ph(Pr/Ph) is from 0.762 to 0.991 with a predominance of phytane,suggesting a marine sapropelic source rock under the reduction to strong reduction environment.On the other hand,the parameters representing thermal maturity of biomarkers,such as Pr/nC₁₇,Pr/nC₁₈ and MPI,show the great difference between the Ordovician oil in Tahe oilfield and the liquid hydrocarbon in Well Tashen 1.The latter mostly like to the oils in Well Tadong 2 and Well T904 that is believed to come from the Middle and Lower Cambrian source rock.In addition,the liquid hydrocarbon in Well Tashen 1 is characteristic of sterane C₂₇ > C₂₈ << C₂₉ and the isotope of petroleum family composition in the saturated fraction is -29.13‰ to -25.84‰.It can be inferred that the liquid hydrocarbons in the Upper Cambrian dolomite mostly come from the Middle and Lower Cambrian source rock and the high formation pressure is an important reason of the hydrocarbon being preserved in the deep buried formation.