Low maturity coal samples were taken from the Ordos Basin to conduct gold tube thermal simulation experiment in a closed system, and the characteristics of the products were analyzed to find out the fractionation mechanism of carbon isotopes and the causes of abnormal carbon isotopic compositions of natural gas. At the heating rates of 2 °C/h (slow) and 20 °C/h (rapid), the low maturity coal samples of the Ordos Basin had the maximum yields of alkane gas of 302.74 mL/g and 230.16 mL/g, the δ¹³C₁ ranges of −34.8‰ to −23.6‰ and −35.5‰ to −24.0‰; δ¹³C₂ ranges of −28.0‰ to −9.0‰ and −28.9‰ to −8.3‰; and δ¹³C₃ ranges of −25.8‰ to −14.7‰ and −26.4‰ to −13.2‰, respectively. Alkane gas in the thermal simulation products of rapid temperature rise process showed obvious partial reversal of carbon isotope series at 550°C, and at other temperatures showed positive carbon isotope series. In the two heating processes, the δ¹³C₁ turned lighter first and then heavier, and the non-monotonic variation of the δ¹³C₁ values is because the early CH₄ is from different parent materials resulted from heterogeneity of organic matter or the carbon isotope fractionation formed by activation energy difference of early enriched ¹²CH₄ and late enriched ¹³CH₄. The reversal of carbon isotope values of heavy hydrocarbon gas can occur not only in high to over mature shale gas (oil-type gas), but also in coal-derived gas. Through thermal simulation experiment of toluene, it is confirmed that the carbon isotope value of heavy hydrocarbon gas can be reversed and inversed at high to over mature stage. The isotope fractionation effect caused by demethylation and methyl linkage of aromatic hydrocarbons may be an important reason for carbon isotope inversion and reversal of alkane gas at the high to over mature stage.

从鄂尔多斯盆地采集的低成熟度煤样品在密闭系统中进行了金管热模拟实验，分析了产物的特征，找出了碳同位素的分馏机理以及天然气中碳同位素组成异常的原因。 。在2°C / h（缓慢）和20°C / h（快速）的加热速率下，鄂尔多斯盆地的低成熟度煤样品的最高烷烃产量为302.74 mL / g和230.16 mL / g，的δ ¹³ C ^ _1米范围-34.8‰至-23.6‰和-35.5‰至-24.0‰; δ ¹³ C ^ _2米范围-28.0‰至-9.0‰和-28.9‰至-8.3‰; 和δ ¹³ C ^ ₃范围分别为-25.8‰至-14.7‰和-26.4‰至-13.2‰。快速升温过程的热模拟产物中的烷烃气体在550°C时表现出明显的碳同位素系列的部分逆转，而在其他温度下则表现出正的碳同位素系列。在两个加热过程中，δ ¹³ C ^ ₁接通打火机第一，然后重，和的非单调的变化δ ¹³ C ^ _1个值是因为早期的CH ₄是从不同亲本材料造成的有机物或异质早期富集的¹² CH ₄与晚期富集的活化能差形成碳同位素分馏¹³ CH ₄。重烃气体的碳同位素值的反转不仅会发生在高到过成熟的页岩气（油型气）中，而且还会发生在煤衍生的气中。通过甲苯的热模拟实验，可以确定重烃气体的碳同位素值可以在高至成熟阶段逆转和逆转。芳烃的脱甲基和甲基键合引起的同位素分馏作用可能是高到超成熟阶段碳同位素转化和烷烃气体逆转的重要原因。