Comparison of hydrocarbon generation simulation of source rocks in close and open system: A case of oil shale from Lower Jurassic in Qaidam Basin, China

摘要

Hydrocarbon generation simulations of an oil-shale sample from Lower Jurassic in Qaidam Basin, China were carried out in both close and open systems in order to compare the results of two different simulating modes which may make us better understand the process of hydrocarbon generation of source rocks in natural geological conditions. The results in close and open systems show that (1) the yields of hydrocarbon gases, CO2 and H2 in both close and open system are very close when the simulation temperature is lower than 350°C, but yields of the total gases and hydrocarbon gases in open system are lower than those in close system when simulation temperature is equal to or higher than 350°C, which indicates liquid hydrocarbons begin to crack into gases when the simulation temperature higher than 350°C, whereas the yield H2 in open system is higher than that in close system, which may be due to the participation of hydrogen in second cracking of liquid hydrocarbons in close system; (2) the yields of expulsion oil and the total generation oil in open system are both higher than those of close system, whereas the yields of residual oil in open and close systems are very close, but the simulation temperature of the highest yield is 300°C and 350°C, respectively; (3) the total yields of hydrocarbon generation in close and open system are 473.6 kg/t_c and 518.0 kg/t_c, respectively, which suggests the oil-shale unit of the Lower Jurassic in Qaidam Basin of China has great hydrocarbon generation potentials; (4) therefore, it may be more reasonable to evaluate hydrocarbon generation potentials of a basin by using the average value of hydrocarbon generation simulation results of source rocks in both close and open systems.