Abstract: Much of the marine carbonate rocks in China are organic carbon poor (mean organic carbon content values generally <0.20%),but are still regarded as source rocks due to the conventionally proposed minimum organic carbon content required for carbonate source rocks (0.10% or even lower). No commercial accumulation was found related to these carbonate rocks after over ten years of exploration, showing the incorrectness of the above minimum organic carbon content. Obtaining such a low minimum value is caused by the unreasonable hypotheses of high hydrocarbon potential of organic matter in marine carbonate rocks and high expulsion ratio of hydrocarbon from carbonate rocks,by overestimating organic matter lost during maturation of carbonate rocks, and by omitting the hydrocarbon lost during second migration. Integrated consideration of above factors will reach the following: (ⅱ) The minimum organic carbon content for a carbonate source rock should be gained by an analogy in exploration instead of by an experiment. (ⅱ) The minimum organic carbon content values for a carbonate source rock, for a high to over mature source rock, and for a gas source rock are not necessarily lower than those for a mudstone source rock,for a mature source rock, and for an oil source rock respectively. They all should be 0.40%~0.50% at least.

Key words: carbonates, source rock, organic carbon content, China

摘要： 我国存在大量平均有机碳丰度很低(一般小于0.20%)、但仍能达到以往提出的碳酸盐岩烃源岩有机碳丰度下限(一般在0.10%)的碳酸盐岩,多年的勘探未发现其能生成原生工业性油气藏,表明该下限提得过低,原因在于传统观点笼统地认为碳酸盐岩中有机质生烃能力较高、碳酸盐岩排烃率高、提出过高的高演化阶段碳酸盐岩原始有机碳恢复系数,并且未考虑运移散失。在重新考虑这些因素后,认为烃源岩平均有机碳下限指标应主要由实际情况的类比来确定。碳酸盐岩烃源岩、高—过成熟阶段的烃源岩以及气源岩的有机碳丰度下限未必分别明显低于泥岩烃源岩、成熟阶段的烃源岩和油源岩,它们的平均有机碳含量都应在0.40%～0.50%以上。

关键词: 碳酸盐岩, 烃源岩, 有机质类型, 有机碳下限, 有机碳恢复系数