Abstract: In order to study the influence of thermal evolution on the formation and distribution of rearranged hopanes as well as geochemical significance, pyrolysis experiment was conducted on crude oil from the TZ62 well in Tarim Basin. The analytical results showed that thermal maturity played an important role on the formation and distribution of rearranged hopanes. At the experimental temperature of 400 ℃ to 500 ℃,with the increase of degree of thermal evolution, the thermal cracking of microcrystalline wax and the thermal degradation of the asphaltene in crude oil have made a main contribution to the formation of rearranged hopanes. Peak oil cracking was corresponding to the experimental temperature at 500 ℃ to 550 ℃,and hopanoids concentrations decreased obviously. Furthermore, 17αhopane had a faster rate of thermal cracking than rearranged hopanes during peak oil cracking stage. Higher degree of thermal evolution played an important role in methyl rearrangement during the experimental temperature increasing from 550 ℃ to 600 ℃. Rearranged hopanes parameters (17αdiahopane/17αhopane, Ts/Tm) were nearly unchanged when the experimental temperature ranges from 400 ℃ to 500 ℃. Rearranged hopanes parameters increased gradually while experimental temperature ranging from 500 ℃ to 550 ℃(corresponding peak oil cracking). However, the parameters then shows an apparent reversal at the temperature of 550 ℃ to 600 ℃. The reversal in these parameters was mainly the result that 17αhopane had faster rate of hydrocarbon generation than rearranged hopanes. Rearranged hopanes parameters can be used as effective maturity parameters at the stage of the late oil window to peak oil cracking.

Key words: crude oil, pyrolysis experiment, rearranged hopane, maturity, geochemical significance