Chemical Kinetics of Carbon Isotope Fractionation of Oil-Cracking Methane and Its Initial Application
LU Shuang-fang, LI Ji-jun, XUE Hai-tao, XU Li-heng Daqing Petroleum Institute, Daqing, Heilongjiang 163318, China
By means of the gold tube thermal simulation equipments, 2 oil samples from Tarim Basin are carried out pyrolysis under high pressure and constant heating rate. Combining GC and carbon isotope analysis, the relationship between generation ratio of and carbon isotope ratio of methane and simulating temperature along with heating rate can be obtained. Based on the experiments above, the chemical kinetic models of methane generated from oil and its fractionation of carbon isotope are constructed and calibrated. The results indicate that the average value and distribution range of activation energy of methane generation are similar for the two oil samples with insignificant difference in distributional manner. The average activation energy of ~ 12 CH_4 generation is a little bit lower than that of the corresponding ~ 13 CH_4 because of relatively higher in low part of activation energy distribution of ~ 12 CH_4 compared to that of ~ 13 CH_4. There is a tiny difference between the activation energy distribution of ~ 12 CH_4 and ~ 13 CH_4 gene- ration that results the obvious fractionation of carbon isotope of the methane generated. The initial application of the calibrated models in Tarim Basin suggests that the gas pools in well Yingnan 2 comes mainly from the partial accumulation in late-and recent-period, and that of well Mandong 1 is cumulated gas.