含水饱和度对灰岩热解生成CO2气产率和碳同位素的影响

Influence of Water Saturation on Generation of CO_2 and Its Carbon Isotope Fractionation from Limestone Pyrolysis

以琼东南盆地的前第三系1块基底灰岩样品为替代样品,应用热模拟实验方法,进行了一系列不同含水条件下的热解实验,并对实验产物CO2的产率和碳同位素进行了分析,探讨了莺歌海盆地基底灰岩的生气情况。结果表明,水的存在与否、含水量的多少均对灰岩热解生成CO2有重大影响。水可以促进灰岩热解生成CO2气体,并能够极大地降低灰岩的热解温度。与无水条件相比,含水条件下灰岩热解产物CO2的碳同位素明显变轻。通过与前人钙质泥岩热解实验对比,并结合莺歌海盆地实际地质资料,研究认为莺歌海盆地CO2气藏可能主要来源于中新统海相钙质泥岩,而前第三系基底灰岩的贡献很少。

A pre-Tertiary limestone sampled from the Qiongdongnan basin,South China Sea, was pyrolyzed Under conditions of different water saturations to compare their differences in carbon dioxide generation and carbon isotope fraetionation. The result shows that the presence of water and its amount significantly affect the generation of thermogenic carbon dioxide. Water not only improves carbon dioxide formation, but also reduces the temperature of limestone decomposition. With comparison of no water in pyrolysis,water causes the isotopically lighter carbon of CO2 from limestone decomposition. Combined with the previous pyrolysis results of calcareous shales and the geological and geochemical data of Yinggehai basin, these suggest that the inorganic carbon dioxide would mainly originate from the lower Miocene calcareous shales and the contribution of pre -Tertiary limestone was less important.