Kinetics of oil-cracking of different types of marine oils from Tahe Oilfield, Tarim Basin, NW China

The C1-C5 gas generation, carbon isotope ratios during cracking of heavy, normal and high-waxy marine oils from Tahe Oilfield, Tarim Basin, NW China, were described with closed-gold tube under high pressure. Three types of oil have similar gas-generation process, with C1 yield increasing with pyrolytic temperature and C2-C5 yield increasing at first then decreasing with the temperature. Heavy-waxy oil has the highest C1-C5 yield of 510mg/g Chinese Character , whereas heavy oil has the lowest C1-C5 yield of 316mg/gChinese Character. The δ13C1 value was light at first, but gradually became heavier with the increase of pyrolytic temperature. However, the δ13C2 and δ13C3 values gradually became heavier when the temperature was greater than 420℃. Using kinetics software, the kinetic parameters of C1-C5 of different type of marine oils were calculated. With the frequency factor of about 1.78×1014s-1, the distribution of the activation energy of C1-C5 mass formation was relatively narrow, with the range from 56 to 66kcal/mol. Among the three types of oil, heavy oil has the widest activation energy distribution, with the lowest major frequency of activation energy. Based on the kinetic parameters, in combination with the fractional conversion(C)of oil to gas, the maximum temperature at which oil can be preserved as a separate oil phase varies from about 178℃ at geological slow heating rates to 206℃ at geological fast heating rates. The existence of Middle Cambrian volatile reservoir of well Zhongshen 1 from Tazhong Uplift provided a strong evidence for the conclusion. ©, 2015, Science Press. All right reserved.