TRACING ORGANIC-INORGANIC INTERACTIONS BY LIGHT STABLE ISOTOPES (H, Li, B, O) OF AN OIL-BEARING SHALE AND ITS CLAY FRACTION DURING HYDROUS PYROLYSIS
TRACING ORGANIC-INORGANIC INTERACTIONS BY LIGHT STABLE ISOTOPES (H, Li, B, O) OF AN OIL-BEARING SHALE AND ITS CLAY FRACTION DURING HYDROUS PYROLYSIS
复制标题
DOI：
10.1007/s42860-021-00163-4
复制
发表时间：
2021-12
影响因子：
2.2
通讯作者：
N. Clauer;L. Williams;A. Fallick
中科院分区：
文献类型：
--
作者：
N. Clauer;L. Williams;A. Fallick
追踪埋藏诱导的有机物成熟和相关粘土物质蚀变过程中的相互作用对于了解单个和组合的矿物和有机过程至关重要。在本研究中，轻元素B，Li，O和H的样品从石油倾向的始新世Kreyenhagen页岩圣华金盆地（加州）进行了检查。自然埋藏引起的温度升高是通过热解实验模拟的，热解实验的温度逐渐升高（270-365°C），持续时间不同（72-216小时），适用于整个岩石及其<2 μm的部分。伊利石结构以及伊利石-蒙皂石混合层的富钾夹层没有受到热解实验的影响，富蒙皂石夹层没有塌陷，但可溶性矿物和有机质发生了改变。未处理的全岩及其热解当量的稀土元素（RE）的分布模式在分析不确定性，这证实了热解实验引起的变化是最小的散装样品。而<2 μm组分的稀土元素则发生了明显的变化，表明全岩和<2 μm组分可能含有不同类型的有机质。此外，只有碳酸盐，氧化物，氯化物，和有机物一起受到影响的伊利石-蒙皂石结构的蒙脱石丰富的夹层。沥青涂层的蒙皂石夹层可能增加了有机来源的B在其网站。随着热解温度的升高，排烃相的δ 11 B和δ 7 Li以及烃类流体的B和Li含量发生变化。根据热解粘土组分的δ 11 B和δ 7 Li，连续释放的B不是同位素均匀的，这可能取决于在连续热解步骤中有机质的类型如何分解，以及释放的组分。有机硼的δ ~（11）B从低温时的-2‰逐渐增加到高温时的+9‰。相对于作为参考的露头样品的值，计算的释放的δ 7 Li也增加，但它几乎保持不变，从310°C下72 h的-7‰到365°C下216 h的-8‰。在300°C以上热解过程中，<2 μm粒级的δ 18 O值显著降低，而δD值变化不大。热解至300°C后，总有机碳（TOC）保持统计学上的恒定，δ 7 Li值也是如此。在本研究中的热解实验表明，沥青涂层蒙脱石夹层的存在下，可能已被误认为脱水蒙脱石在文献中。与异常伊利石K-Ar年龄一起，在源岩和储集岩中出现的这种沥青包裹的伊利石-蒙皂石夹层的出现可以指示相对于伊利石化的烃成熟时间。
Tracing interactions during burial-induced organic maturation and associated clay-material alteration is of prime importance for understanding both the individual and combined mineral and organic processes. In the present study the light elements B, Li, O, and H of a sample from oil-prone Eocene Kreyenhagen Shale from San Joaquin Basin (California) were examined. The natural burial-induced temperature increase was simulated by pyrolysis experiments at progressively increasing temperatures (270–365°C) and for varied durations (72–216 h) applied to the whole rock and its <2 μm fraction. The illite structure as well as the K-rich interlayers of the illite-smectite mixed layers were not affected by the pyrolysis experiments and the smectite-rich interlayers did not collapse, while the soluble minerals and the organic matter were altered. The distribution pattern of the rare-earth elements (REEs) from untreated whole rock and of its pyrolyzed equivalents are within analytical uncertainty, which confirms that the changes induced by pyrolysis experiments were minimal in the bulk sample. Conversely, the REEs from the <2 μm fractions were modified significantly, suggesting that the whole rocks and the <2 μm fractions may contain different types of organic materials. Also, only the carbonates, oxides, chlorides, and organic matter were affected together with the smectite-rich interlayers of the illite-smectite structure. Bitumen coating of the smectite interlayers probably increased the amount of B of organic origin in their sites. The δ11B and δ7Li of the successively expelled hydrocarbon phases changed with increasing pyrolysis temperatures, together with the B and Li contents of the hydrocarbon-related fluids. On the basis of the δ11B and δ7Li from pyrolyzed clay fractions, the B released successively was not isotopically homogeneous, probably depending on how the type of organic matter decomposed during the successive pyrolysis steps, and on which components were released. The δ11B of organic-B increased progressively from –2‰ at low experimental temperature up to +9‰ at the highest temperature. The calculated δ7Li that was released also increased relative to the value of the outcropping sample used as a reference, but it remained almost constant from –7‰ at 310°C for 72 h to –8‰ at 365°C for 216 h. The δ18O values of the <2 μm size fractions decreased significantly during pyrolysis above 300°C, but the δD changes were rather modest. The total organic carbon (TOC) remained statistically constant after pyrolysis to 300°C, as did the δ7Li values. The pyrolysis experiments in the present study suggest the presence of bitumen-coated smectite interlayers that could have been misidentified as dehydrated smectite in the literature. Together with abnormal illite K-Ar ages, the occurrence of such bitumen-coated illite-smectite interlayers occurring in source and reservoir rocks could indicate the timing of hydrocarbon maturation relative to illitization.