The primary migration of petroleum has been recently described in detail for a thermally mature core of the Barnett Shale with almost nonvariant organofacies and maturity. Here, we use samples from the same well to provide new insights into the fractionation of pyrrolic nitrogen compounds during primary migration. Using gas chromatography–mass spectrometry (GC-MS), a decrease in concentration of carbazoles and benzocarbazoles was observed which correlated with migration distance. However, a preferential removal of individual isomers like benzocarbazole[a] relative to benzocarbazole[c] could not be detected. Enlarging the analytical window, we studied the effect of primary migration on high molecular weight nitrogen-containing compounds using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) combined with electrospray ionization (ESI) in the negative ion mode. Compounds with one or two nitrogen atoms are most abundant. Among the N₁ compounds, those with 12, 15, 18, 20, and 23 double bond equivalents (DBEs) were dominating classes representing carbazole-type compounds (among others) with one to three ortho-annelated benzene rings (12, 15, and 18) and four to five ortho- and peri-annelated benzene rings (20, 23). In comparison, the N₂ compound class mainly consists of compounds with 12, 15, 17, 20, and 23 DBEs representing (among other compounds) biindoles with zero to one ortho-annelated benzene ring (12, 15) and carbazolocarbazoles with zero to two ortho-annelated benzene rings (17, 20, and 23). A relative enrichment of biindole-type compounds relative to carbazolocarbazoles in migrated petroleum was shown. This might indicate that aromatic compounds with separated ring systems like biindoles are less strong retained in the source rock than fully annelated polycyclic aromatic compounds like carbazolocarbazoles. Within individual DBE classes of N₁ and N₂ compounds, very similar carbon number (CN) distributions were illustrated for nonmigrated and migrated fluids, i.e., a predominance of C_0–5 alkylated homologues maximizing at C₂ or C₃ substitutes. Regardless of fractionation, the overall similar distributions in DBE and CN suggest that pyrrolic nitrogen-containing compounds have restricted precursors and common mechanisms of formation. Nonfluorescent chlorophyll catabolites (NCCs), the final breakdown products of chlorophyll, were tentatively suggested as possible precursors.

中文翻译：

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德克萨斯州马拉松1豆科灌木油井的Barnett页岩序列内石油初次迁移过程中的吡咯氮化合物化合物的分馏

最近，对Barnett页岩的热成熟岩心（几乎没有变化的有机相和成熟度）进行了石油的主要运移的详细描述。在这里，我们使用同一口井中的样品，以提供有关初级迁移过程中吡咯含氮化合物分馏的新见解。使用气相色谱-质谱法（GC-MS），观察到咔唑和苯并咔唑的浓度降低，这与迁移距离相关。但是，无法检测到相对于苯并咔唑[c]优先去除个别异构体，如苯并咔唑[a]。扩大分析范围，我们使用负离子模式结合傅里叶变换离子回旋共振质谱（FT-ICR-MS）和电喷雾电离（ESI）研究了初级迁移对高分子量含氮化合物的影响。具有一个或两个氮原子的化合物含量最高。在N之中_1种化合物（具有12、15、18、20和23双键当量（DBE）的化合物）占主导地位，代表具有1至3个邻苯环（12、15和18）的咔唑类化合物（除其他外）以及四到五个邻位和周边退火的苯环（20、23）。相比之下，N ₂类化合物主要由具有12个，15个，17个，20个和23个DBE的化合物组成，这些DBE代表（除其他化合物外）具有0到1个邻苯环（12、15 ）的双吲哚和具有0到0的邻氨基苯并咔唑。两个邻-退火的苯环（17、20和23）。显示了在迁移的石油中，相对于咔唑咔唑，双吲哚型化合物相对富集。这可能表明具有分开的环系统的芳族化合物（如双吲哚）与完全退火的多环芳族化合物（如咔唑咔唑）相比保留在烃源岩中的强度较低。在单个DBE类别的N ₁和N ₂化合物中，对于非迁移和迁移的流体显示出非常相似的碳数（CN）分布，即，占优势的C _0-5烷基化同系物在C ₂或C ₃处最大化替代品。无论分馏如何，DBE和CN中总体上相似的分布表明，吡咯含氮化合物具有受限的前体和常见的形成机理。初步建议将非荧光叶绿素分解代谢物（NCC）作为叶绿素的最终分解产物。