煤中金刚烷的分布与演化

金刚烷的浓度和指数是研究深层油藏裂解程度和成熟度的重要参数，由于金刚烷的形成机理不明，制约了金刚烷化合物在深层油气地球化学中的应用。通过对华北地区镜质体反射率（R_o）在0.55%~5.32%的二叠系煤样开展金刚烷色谱-质谱定量分析，发现低成熟煤样中存在单金刚烷系列化合物，而煤样中双金刚烷、三金刚烷和四金刚烷系列化合物的检出所对应的R_o分别为0.81%、1.82%和2.59%。这表明不同笼数金刚烷的生成具有阶段性，笼数越高，其所对应的烃源岩成熟度越高。定量分析结果表明，煤样在R_o为0.55%~3.01%时为金刚烷生成阶段，煤样在R_o>3.01%时对应金刚烷裂解阶段，其中，当R_o>2.71%，单金刚烷系列和双金刚烷系列的组成发生变化。金刚烷参数，如二甲基单金刚烷指数1（DMAI1）、二甲基单金刚烷指数2（DMAI2）、三甲基单金刚烷指数1（TMAI1）、三甲基单金刚烷指数2（TMAI2）以及乙基单金刚烷（EA）参数1-EA/（1-EA＋2-EA）]，与R_o在0.55%~3.01%阶段具有较好的正相关。金刚烷产率的比值，如二甲基单金刚烷系列与二甲基双金刚烷系列比值、甲基单金刚烷系列与甲基双金刚烷系列比值、单金刚烷系列与双金刚烷系列比值以及单金刚烷与双金刚烷比值，与R_o在0.81%~4.28%阶段具有明显的负相关关系，表明这些参数可以用作评价成熟度的良好指标。

Distribution and evolution of diamondoids in coals

The concentration and index of diamondoids are the key parameters for evaluating the cracking degree and maturity of deep reservoirs. The formation mechanism of diamondoids is unknown, which restricts the application of diamondoid compounds in petroleum geochemical exploration of deep strata. Through the quantitative analysis of diamondoids by gas chromatography-mass spectrometry on the Permian coal samples with the vitrinite reflectance (R_o) of 0.55%-5.32% in North China, it was found that the adamantane series existed in the low-mature coal samples. The R_o corresponding to the diamantane, triamantane and tetramantane series in the coal samples were 0.81%, 1.82% and 2.59%, respectively. This indicates the staged generation of diamondoids with different cage units. The higher the cage unit is, the higher the corresponding maturity of the source rock will be. The quantitative analysis results show that the R_o of coal sample in the range of 0.55%-3.01% indicate the generation stage of diamondoids, while the R_o greater than 3.01% indicates the cracking stage of diamondoids. When R_o>2.71%, the composition of the adamantane and diamantane series changed. Diamondoid parameters, such as the dimethyladamantane index 1 (DMAI1), dimethyladamantane index 2 (DMAI2), trimethyladamantane index 1 (TMAI1), trimethyladamantane index 2 (TMAI2) and ethyladamantane (EA) parameter1-EA/(1-EA+2-EA)], have a good positive correlation with R_o in the range of 0.55%-3.01%. The ratios of diamondoid yield, such as the ratio of dimethyl adamantanes series to dimethyl diamantanes series, the ratio of methyl adamantanes series to methyl diamantanes series, the ratio of adamantanes series to diamantanes series and the ratio of adamantine to diamantane, has a significant negative correlation with R_o in the range of 0.81%-4.28%, indicating that these parameters can be used as good indicators for evaluating the maturity of source rock.