Petroleum alteration by thermochemical sulfate reduction – A comprehensive molecular study of aromatic hydrocarbons and polar compounds
Petroleum alteration by thermochemical sulfate reduction – A comprehensive molecular study of aromatic hydrocarbons and polar compounds
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DOI：
10.1016/j.gca.2014.11.021
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发表时间：
2015-03
影响因子：
5
通讯作者：
C. Walters;F. C. Wang;K. Qian;Chunping Wu;Anthony S Mennito;Zhibin Wei
中科院分区：
文献类型：
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作者：
C. Walters;F. C. Wang;K. Qian;Chunping Wu;Anthony S Mennito;Zhibin Wei
热化学硫酸盐还原(TSR)在将碳氢化合物完全氧化为二氧化碳的过程中会改变石油的组成。TSR对挥发性物质的分子和同位素组成的影响是众所周知的，然而，对于非挥发性的高相对分子质量的芳香族和极性物种还没有很好的文献报道。为了解决这一缺陷，一套由Smackover碳酸盐生成并积累的陆上墨西哥湾沿岸石油和凝析油被组装起来，其中包括经历不同程度的TSR蚀变和储层热裂解的样品。用气相色谱和APPI-FTICR-MS对芳烃类化合物和NSO物种的全分子组成进行了表征和半定量，其中硫代蒙脱石的浓度是TSR变化程度的可靠指标。一旦由TSR生成，除最极端的储集层温度(>；180°C)外，硫钻石蒙脱石类化合物在所有环境中都保持热稳定。油气浓度和分布受热裂化和TSR的影响。随着TSR蚀变程度的增加，原油中单芳烃的含量增加，高相对分子质量芳烃的分布向更稠密的物种转移，烷基碳氢化合物的数量减少。有机硫化合物由TSR过程产生。除了先前研究中提到的苯并噻吩类和二苯并噻吩类化合物的增加外，TSR还产生了含有一个或多个硫原子的缩合物种，这些硫原子可能由一个或多个噻吩核组成。我们推测，这些物种是由多环芳烃的部分氧化和脱烷基化反应产生的，然后是硫掺入和缩合反应。TSR蚀变油中残留的有机硫是“原固体沥青”，进一步冷凝、氧化或硫掺入生成高硫固体沥青，这在化学上有别于热裂解反应形成的焦油。尽管TSR涉及烃类氧化成CO2，但以前对TSR蚀变油的研究尚未鉴定出中间产物。利用NESI-FTIRC-MS，含氧物种的存在和分布变得明显。所有的油都含有少量的O2和O4物种，推测单环烷酸和双环烷酸来自源头。随着TSR的进展，含氧物种的分布向含氧量更高的物种转移，最高可达O8。观察到SOx物种也有类似的趋势。我们假设这些是部分氧化的凝聚烃，这些物种很可能是由Püttmann等人提出的反应形成的。(1989)对与Kupferschiefer矿化有关的多环芳烃的氧化，其中具有芳基-芳基键的碳氢化合物与硫结合形成噻吩类物种。TSR的速度受储层温度和硫化氢的存在的影响。通常，需要较高的储层温度(>；140°C)才能发生广泛的TSR蚀变。来自Gin Creek油田的石油似乎收到了硫化氢的电荷，推测来自向下倾斜储层的Tsr蚀变，这加速了相对较冷的储层内的Tsr反应(∼109°C)。这种条件允许产生和保存大量的含硫物种，这些物种在更高的温度下会被热裂解。
Thermochemical sulfate reduction (TSR) alters petroleum composition as it proceeds towards the complete oxidation of hydrocarbons to CO2. The effects of TSR on the molecular and isotopic composition of volatile species are well known; however, the non-volatile higher molecular weight aromatic and polar species have not been well documented. To address this deficiency, a suite of onshore Gulf coast oils and condensates generated from and accumulating in Smackover carbonates was assembled to include samples that experienced varying levels of TSR alteration and in reservoir thermal cracking. The entire molecular composition of aromatic hydrocarbons and NSO species were characterized and semi-quantified using comprehensive GC × GC (FID and CSD) and APPI–FTICR-MS.The concentration of thiadiamondoids is a reliable indicator of the extent of TSR alteration. Once generated by TSR, thiadiamondoids remain thermally stable in all but the most extreme reservoir temperatures (>180 °C). Hydrocarbon concentrations and distributions are influenced by thermal cracking and TSR. With increasing TSR alteration, oils become enriched in monoaromatic hydrocarbons and the distribution of high molecular weight aromatic hydrocarbons shifts towards more condensed species with a decrease in the number of alkyl carbons. Organosulfur compounds are created by the TSR process. In addition to the increase in benzothiophenes and dibenzothiophenes noted in previous studies, TSR generates condensed species containing one or more sulfur atoms that likely are composed of a single or multiple thiophenic cores. We hypothesize that these species are generated from the partial oxidation of PAHs and dealkylation reactions, followed by sulfur incorporation and condensation reactions. The organosulfur species remaining in the TSR altered oils are “proto-solid bitumen” moieties that upon further condensation, oxidation or sulfur incorporation result in highly sulfur enriched solid bitumen, which is chemically distinct from pyrobitumen formed by thermal cracking reactions.Although TSR involves the oxidation of hydrocarbons to CO2, prior studies of TSR-altered oils have not identified intermediate products. Using NESI–FTIRC-MS, the presence and distribution of oxygenated species become evident. All oils possess minor amounts of O2and O4species, presumable mono- and di-naphthenic acids originating from the source. As TSR progresses, the distribution of oxygenated species shifts towards increasing species with higher oxygen content, up to O8. Similar trends are observed for the SOxspecies. We hypothesize that these are partially oxidized condensed hydrocarbons and that these species are likely formed by the reaction proposed by Püttmann et al. (1989) for the oxidation of PAHs associated with Kupferschiefer mineralization, whereby hydrocarbons with aryl–aryl bonds incorporate sulfur to form thiophenic species.The rate of TSR is influenced by reservoir temperature and the presence of H2S. Typically, high reservoir temperatures (>140 °C) are needed for extensive TSR alteration to occur. Oil from the Gin Creek Field appears to have received a charge of H2S, presumably from TSR alteration of a down dip reservoir, which has accelerated the TSR reaction within a relatively cold reservoir (∼109 °C). This condition has allowed for the generation and preservation of abundant sulfur containing species that would be thermally cracked at higher temperatures.