对碳酸盐生油岩的有机质丰度及其演化特征的讨论

碳酸盐生油岩的有机质丰度下限问题存在不少的争议,它关系到碳酸盐沉积区的含油气远景评价,因而需要进一步加强研究。我国大部分碳酸盐生油岩(不含泥质)的剩余有机碳含量较低.平均为0.1—0.2%,但烃类含量可达100—200ppm。吉曼概括了世界上页岩和石灰岩生油岩的平均有机碳及烃的含量:页岩有机碳及烃的平均含量分别为1.14%和96ppm;石灰岩则分别为0.24%和98ppm。 

RICHNESS OF ORGANIC MATTER AND ITS EVOLUTIONAL CHARACTERISTICS IN CARBONATE SOURCE ROCKS

For a long time, there is an argument about the lower limit of the richness of organic matter for a carbonate to be source rocks. It is a key problem in evaluating oil and gas prospects in carbonate rock area. However, the richness indicators for carbonate source rocks used in China are set on lower levels. Based on a preliminary study on the richness and loss of organic carbon during thermal evolution, considering the difference of diagenesis between shales and carbonate rocks, it is suitable to take 0.3-0.5% as the lower limit of organic carbon and 100 ppm or more as that of hydrocarbon content. Thermal simulation experiments on several samples showed that the threshold of carbonate source rocks is at about 420℃, but the lower limit is at 470℃ which was acquired from the maximum pyrolysls temperature. The experiment also shows that the hydrocarbon content decreases with thermal evolution and 8-9% organic carbon was lost during the whole maturation stage. Organic carbon loss increased to 16% In the mid-period of overmaturation stage and 20% at the later stage.