THE TWO-STAGE FRACTIONATION MODEL OF METHANE CARBON ISOTOPE FROM THE THERMAL SIMULATION EXPERIMENTS OF SOURCE ROCKS IN THE KUQA DEPRESSION OF THE TARIM BASIN
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摘要: 选用塔里木盆地库车坳陷三叠系和侏罗系的煤、黑色泥岩及碳质泥岩等样品进行了260~540℃之间的生烃热模拟实验,模拟温阶为40℃,并对产物中天然气的碳同位素和实验后的固态产物的镜质体反射率进行了测定,得到了模拟气态烃产物中甲烷的碳同位素与模拟产物成熟度Ro的关系。实验表明,在烃源岩由未成熟到过成熟的演化过程中,甲烷碳同位素存在二阶分馏,在未熟到成熟(Ro<1.5%)阶段,甲烷碳同位素随温度(成熟度)的增加由重变轻,而在成熟到过熟阶段,甲烷碳同位素随温度(成熟度)的增加由轻变重,在这2个演化阶段甲烷碳同位素与Ro均呈线性相关。Abstract: Thermal simulation experiments of hydrocarbon generation on coal,mudstone and carbargilite samples of Triassic and Jurassic from the Kuqa Depression in the Tarim Basin were carried out through the temperature from 260 to 540℃ with 40℃ as increment.Carbon isotope of the generated gas and vitrinite reflectance(Ro) of post-experiment solid product were measured.The relationship between carbon isotopic values of methane in gaseous hydrocarbon and maturity of solid products was also obtained.The results of the experiment showed that there is two-stage model of isotopic fractionation during source rock evolution.During immature to mature phase(Ro1.5%),carbon isotopic values of methane became lighter with the increase of temperature(maturity).On the contrary,during mature to overmature phase,it became heavier with the increase of temperature(maturity).However,both in the above two phases,carbon isotopic values of methane and maturity were in linear relation.
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