鄂尔多斯盆地奥陶系海相碳酸盐岩生烃性能与中部长庆气田气源成因研究

Research on Hydrocarbon Generation of Ordovician Marine Carbonatite of the Ordos Basin and Genesis of Changqing Gas Fields

用激光 -荧光显微镜等有机岩石学方法 ,挑选样品中有明显生、排烃现象的碳酸盐岩 ,再以测定的这类碳酸盐岩的有机碳含量为依据 ,确定本区高成熟碳酸盐气源岩残余有机碳的下限指标用 0 .13%～ 0 .14 %比较合理。根据碳酸盐岩储层孔隙中充填沥青和皮膜状残余沥青的分布和含量 ,论证了陕参 1井等奥陶系碳酸盐岩地层在地质历史中 ,存在若干油气有效储层。采用连续升温 ,步进取样的热模拟实验方法 ,揭示了本区煤与碳酸盐岩干酪根随热演化作用增强 ,烃类气体产物的干燥系数增大 ,δ1 3C1 、δ1 3C2 明显变重的规律 ,并根据样品实验结果推算 ,本区石炭系—二叠系煤最大生气阶段的δ1 3C1 应为 - 2 7‰～ - 2 8‰ ,碳酸盐岩最大生气阶段的δ1 3C1 应为- 31.7‰～ - 33‰。在气源成因判识中 ,根据主生气期阶段对天然气成藏储聚的贡献最大、甲烷碳同位素较重以及长庆气田风化壳气藏天然气δ1 3C1 重值区并不与石炭系—二叠系煤的镜质组反射率高值区匹配的现象等进行气源判识 ,认为长庆奥陶系风化壳气藏 。

On the basis of observation of hydrocarbon generation and selection of carbonate rock samples by using the laser fluorescence microscopy, it is determined that the lower limit of the residual TOC content of highly mature carbonate of gas source rocks in this area is 0.13%~0.14%. According to the content and distribution of filling bitumen and crustiform residual bitumen, it is demonstrate that there exist effective reservoir rocks of oil and gas in the Ordovician strata of well SC-1 and other wells. Simulation results of continuous heating and stepwise sampling indicate that the dryness parameters of hydrocarbon gases are becoming larger and carbon isotopes of methane and ethane (δ 13C 1 and δ 13C 2) becoming heavier with the progress of the thermal evolution of coal and carbonate Kerogen in this area. It is estimated that the main gas generation stage of the coal corresponds to the period when the carbon isotope of methane (δ 13C 1) ranges between -27‰ and -28‰ and the main gas generation stage of carbonate kerogen corresponds to the period when the carbon isotope of methane (δ 13C 1) is from -31.7‰ to -33.0‰. As regards the identification of gas sources, we hold that the Changqing Ordovician oil pool is a weathering reservoir with mixed sources of Upper-Palaeozoic coal (C-P) and Lower-Palaeozoic marine carbonate. This conclusion is based on the fact that the main gas-generation period has the most contribution to the gas accumulation with heavier carbon isotope of methane and that the distribution of heavier methane carbon isotope does not correspond to the distribution of high vitrinite reflectance (Ro%) of the C-P coal.