原油热模拟实验中重排藿烷类变化特征及其意义

通过对TZ62井原油进行热模拟实验，探讨热演化程度对原油中重排藿烷类化合物形成分布的影响及其地球化学意义。实验发现：在400～500 ℃阶段，随着热演化程度的增加，原油中高碳数微晶蜡类长链化合物热裂解和原油中的沥青质热降解作用对重排藿烷的形成具有贡献作用。在500～550 ℃对应的原油裂解高峰阶段，藿烷类化合物浓度明显降低，且17α(H)-藿烷比重排藿烷类化合物具有更快的热裂解速率。在温度为550～600 ℃阶段，较高的热演化程度对17α(H)-藿烷甲基重排作用形成重排藿烷具有贡献作用。重排藿烷参数(17α(H)-重排藿烷/17α(H)-藿烷、Ts/Tm)在400～500 ℃变化较弱，几乎不受热演化程度的影响；在500～550 ℃的原油裂解高峰阶段，逐渐增大；在550～600 ℃发生反转，逐渐减小。重排藿烷参数可作为高成熟阶段原油成熟度判识的有效参数，其有效应用范围是生油窗晚期至原油裂解高峰期。

Rearranged Hopanes Compositions in Pyrolysis Experiment of Crude Oil and Geochemical Significance

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.