烃源岩热模拟实验中重排藿烷类化合物变化特征及其意义

摘要

Pyrolysis experiments were conducted on immature hydrocarbon source rocks from the well PL⁃1 in the Bohai Bay Basin to study the influence of thermal evolution on the formation of rearranged hopanes as well as the relationships among rearranged hopane parameters and thermal evolution. The experimental results showed that re⁃arranged hopanes displayed various characteristics during different thermal evolution stages. The absolute concen⁃tration of rearranged hopanes in pyrolysis at 250 °C increased relative to that of the original sample, and it gradually reduced as experimental temperature increased from 250℃ to 400℃. The higher the degree of thermal evolution was, the greater the proportion of absolute concentration of rearranged hopanes decreased. When the experimental temperature was between 300-400℃, the reduced proportions of the absolute concentration of compounds showed a pattern of 17α( H )⁃hopane>18α( H )⁃neohopane>17α( H )⁃diahopane. In addition, the rearranged hopane parameters (17α(H)⁃diahopane/17α(H)⁃hopane) were nearly unchanged at the stage of low mature to mature, nevertheless it gradually increased at the stage of mature to highly mature. The immature to low mature stage is the main stage of the formation of rearranged hopanes. Higher thermal evolution has an influence on the formation of rearranged hopanes to some degree. Moreover, rearranged hopane parameters can be used as an effective maturity index in the stage of mature to highly mature.%为了探索热演化程度对烃源岩中重排藿烷类化合物形成的影响及其地球化学意义，通过对渤海湾盆地PL⁃1井未成熟烃源岩样品进行热模拟实验研究，分析重排藿烷类化合物组成随热模拟实验温度变化特征以及重排藿烷参数与热演化程度的关系。在烃源岩的不同热演化阶段，重排藿烷类化合物变化特征不同。烃源岩热模拟实验250℃时的重排藿烷绝对浓度相对于烃源岩原样中的重排藿烷绝对浓度略有升高；250～400℃时的重排藿烷绝对浓度均逐渐降低。在热模拟实验中重排藿烷绝对浓度降低比例呈现出高成熟阶段＞成熟阶段＞低成熟阶段的规律；在300～400℃对应的成熟—高成熟阶段，化合物绝对浓度降低幅度呈现出17α（ H）⁃藿烷＞18α（ H）⁃新藿烷＞17α（ H）⁃重排藿烷的特征。17α（ H）⁃重排藿烷参数在低成熟—成熟阶段基本不变，在成熟—高成熟阶段逐渐增大。未成熟—低成熟阶段是重排藿烷类化合物形成的主要阶段，较高的热演化程度对重排藿烷的形成具有一定影响，重排藿烷参数可以作为烃源岩成熟—高成熟阶段有效的成熟度指标。