热力作用对烃源岩中重排藿烷类化合物形成的作用

通过对87个采自鄂尔多斯盆地煤系烃源岩和松辽盆地湖相烃源岩样品进行的地球化学分析结果显示，热力作用对烃源岩重排藿烷组成特征的影响强烈。随成熟度的变化，来自两套沉积体系的烃源岩中重排藿烷相对丰度的分布相似，随成熟度增大17α（H）-重排藿烷和18α（H）-新藿烷相对丰度均先增大后减小，并在R_o:0.80%~0.90%（生油窗）时达峰值。不同沉积环境的烃源岩中重排藿烷的成熟度与绝对浓度的变化规律一致。在R_o:0.50%~0.70%（未熟-低熟）阶段，重排藿烷绝对浓度较大；在R_o:0.70%~0.80%（成熟）阶段，重排藿烷的绝对浓度显著降低。不同沉积环境中重排藿烷的参数随成熟度的变化规律揭示:在重排藿烷的形成过程中，热力作用的影响要强于沉积环境和生物来源。

Thermal Effect on the Distribution of Rearranged Hopanes in Hydrocarbon Source Rocks

The molecular geochemical characteristics of a total 87 samples of lacustrine and coal measure hydrocarbon source rocks collected from the Songliao Basin and Ordos Basin are systematically analyzed in order to evaluate thermal effect on the distribution characteristics of rearranged hopanes in hydrocarbon source rocks. The results indicate that both lacustrine and coal measure hydrocarbon source rocks contain abundantly four series of rearranged hopanes and their distributions in geological bodies from different depositional environments or parent material sources show similar variation trends. The relatively lower abundant rearranged hopanes are distributed from low mature to high mature stages, whereas the abnormally high or higher abundant rearranged hopanes are mainly presented in mature stage. The linear correlations between the 17α(H)-diahopane series and other three series of rearranged hopanes including 18α(H)-neohopane series, the early-eluting rearranged hopane series and 21-methyl-28-nor-hopane series, are diverse clearly. In addition, the variations of relative abundance of rearranged hopanes from the two sets of samples show similar trend. For example, the relative abundances of 17α(H)-diahopane and 18α(H)-neohopane display an initial increase and a following decrease with increasing maturity and the highest amounts appear to be distributed in the range of maturity 0.8%-0.9% R_o. On the other hand, the absolute concentrations of rearranged hopanes have consistent variation for the hydrocarbon source rocks derived from different sedimentary environments with increasing maturity. Rearranged hopanes are formed at immature to mature stage corresponding to R_o=0.5%-0.7%. With the source rocks into mature stage (R_o=0.7%-0.8%), the absolute concentration decreases remarkably with the decreasing extent more than 90%. The consistency of variation of relative abundance and absolute concentration of rearranged hopanes in different depositional systems indicate that thermal effect has much more important impact on the distribution and composition of rearranged hopanes compared with sedimentary environments and biological sources.