Abstract:

Previous studies on the hydrocarbon generation potential of Chang 7 hydrocarbon source rocks in the southern Ordos Basin were mainly focused on analyzing static geochemical parameters. No systematic evaluation of hydrocarbon generation potential has ever been carried out, which limited our understanding of the potential of Chang 7 hydrocarbon source rocks and the shale oil resource distribution. For this reason, rock samples were collected from two types of Chang 7 source rocks for thermal simulation experiments, and comparative analysis was performed on the hydrocarbon generation products, yield characteristics and hydrocarbon generation kinetics. We suggest that: (1)Distribution of activation energy of black shale is more concentrated than that of dark shale, and the peak frequency of activation energy and frequency factor of black shale are lower than those of the dark shale. This indicates that the black shale has the characteristics of short-term rapid hydrocarbon generation. (2)Under geological conditions, R_o values of the black shale during the main hydrocarbon generation period (0.70%~0.87%) are lower than those of the dark shale (1.06%~1.72%). (3) In a closed system, R_o is in the range of 0.9%~1.3%. The total hydrocarbon production rate and the amount of oil produced are both higher in the black shale than in the dark shale. Comprehensive analysis of geochemical data of the dark and black shales suggest that the former is more favorable source rock for shale oil resources in the study area.

Key words: Ordos Basin, pyrolysis experiment, hydrocarbon-generating characteristics, source rocks, Chang 7 member