Chemical characterization of the kerogen from Moroccan Timahdit oil shale by analysis of oxidation products

A 33 step alkaline permanganate degradation of the kerogen from Moroccan Timahdit oil shale (M-Zone) was carried out. A very high total yield of oxidation products was obtained (95.4% based on original kerogen). Detailed GC-MS analyses of ether-soluble acids, acids isolated from aqueous solutions and soluble products of further controlled permanganate dedradation of precipitated, ether-insoluble acids, served as a basis for the quantitative estimation of the participation of various types of products and for comparison with other kerogens. The most interesting finding was the observed uniquely high yield of aromatic oxidation products from an intermediate type I–II kerogen. Taking into account the almost equally dominant aliphatic (50.2%) and aromatic (43.2%) nature of the acidic oxidation products, the existence of an aliphatic cross-linked nucleus mixed with cross-linked aromatic units in the Timahdit shale kerogen is postulated. Uniform distribution of oxidation products throughout the degradation suggested a similar reactivity of the various kerogen constituents towards alkaline permanganate.     

Multistage alkaline permanganate degradation of a type II kerogen

The products of a 27-step alkaline permanganate degradation of a type II kerogen from a sample of Toarcian shale, Paris Basin, have been studied. The high yield of oxidation products consisted of 1.86% neutrals and bases, 24.48% ether-soluble acids, and 45.95% precipitated, ether-insoluble acids, based on weight of original kerogen. The ether-soluble acids and the soluble products of further permanganate degradation of precipitated acids were found to consist mostly of saturated unbranched C₆–C₂₂ α,ω-dicarboxylic and C₉–C₂₅ monocarboxylic acids. Significant amounts of aromatic monocarboxylic, dicarboxylic and tricarboxylic acids were also found. Alkane tri- and tetracarboxylic acids were obtained in small concentration.     

Improvement of kerogen structural interpretations based on oxidation products isolated from aqueous solutions

A detailed investigation of kerogen oxidation products remaining in aqueous solutions after the usual isolation of degradation products by extraction with ether or precipitation, was carried out for the first time in kerogen structural studies. Three shale samples were investigated: Green River shale (type I kerogen), Toarcian shale, Paris Basin (type II), and Mannville shale, Canada (type III). The yields of acids from aqueous solutions were noticeable: 12.98, 15.32 and 22.32%, respectively, based on initial kerogens. Qualitative and quantitative capillary GC/MS analysis showed that the ratios of different kinds of identified acids depended much on the type of precursor kerogen. Some of the acids identified in aqueous solutions have not been found earlier among the degradation products of the same kerogen samples, or were obtained in different ranges and yields. Consequently, slight modifications were suggested of the image on the nature of various types of kerogens based on examination of ether-soluble acids only. Namely, slightly higher proportions of aromatic and alkane-polycarboxylic acids in the total oxidation products of both type I and type II kerogens indicated larger participation of aromatic and alicyclic and/or heterocyclic structures in these two kerogens. On the other hand, for type III Mannville shale kerogen, a somewhat larger share of aliphatic type structures was demonstrated.     

Molecular Structure of Kerogen in the Longmaxi Shale: Insights from Solid State NMR,FT‐IR,XRD and HRTEM

Kerogen plays an important role in shale gas adsorption, desorption and diffusion. Therefore, it is necessary to characterize the molecular structure of kerogen. In this study, four kerogen samples were isolated from the organic-rich shale of the Longmaxi Formation. Raman spectroscopy was used to determine the maturity of these kerogen samples. High-resolution transmission electron microscopy (HRTEM), 13C nuclear magnetic resonance (13C NMR) , X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy were conducted to characterize the molecular structure of the shale samples. The results demonstrate that VReqv of these kerogen samples vary from 2.3% to 2.8%, suggesting that all the kerogen samples are in the dry gas window. The macromolecular carbon skeleton of the Longmaxi Formation kerogen is mainly aromatic (fa’=0.56). In addition, the aromatic structural units are mainly composed of naphthalene (23%), anthracene (23%) and phenanthrene (29%). However, the aliphatic structure of the kerogen macromolecules is relatively low (fal*+falH=0.08), which is presumed to be distributed in the form of methyl and short aliphatic chains at the edge of the aromatic units. The oxygen-containing functional groups in the macromolecules are mainly present in the form of carbonyl groups (fac=0.23) and hydroxyl groups or ether groups (falO=0.13). The crystallite structural parameters of kerogen, including the stacking height (Lc=22.84 ?), average lateral size (La=29.29 ?) and interlayer spacing (d002=3.43 ?), are close to the aromatic structural parameters of anthracite or overmature kerogen. High-resolution transmission electron microscopy reveals that the aromatic structure is well oriented, and more than 65% of the diffractive aromatic layers are concentrated in the main direction. Due to the continuous deep burial, the longer aliphatic chains and oxygen-containing functional groups in the kerogen are substantially depleted. However, the ductility and stacking degree of the aromatic structure increases during thermal evolution. This study provides quantitative information on the molecular structure of kerogen samples based on multiple research methods, which may contribute to an improved understanding of the organic pores in black shale.     

Changes in the composition of bitumen extracts and chemical structure of kerogen during hydrous pyrolysis

The paper presents data on the composition of biomarkers from bitumen extracts and the chemical structure of kerogen from C_org-rich sedimentary rocks before and after hydrothermal treatment in an autoclave at 300°C. Samples selected for this study are kukersite and Ordovician Dictyonema shale from the Baltics, Domanik oil shale from the Ukhta region, Upper Permian brown coal from the Pre-Ural foredeep, carbonaceous shale from the Oxfordian horizon of the Russian plate, and Upper Jurassic oil shales from the Sysola oil shale bearing region. The rocks contain type I, II, III, and II-S kerogens. The highest yield of extractable bitumen is achieved for Type II-S kerogen, whereas Type III kerogen produces the lowest amount of bitumen. The stages of organic matter thermal maturation achieved during the experiments correspond to a transition from PC_2–3 to MC_1–2. The ¹³C NMR data on kerogen indicate that the aromatic structures of geopolymers underwent significant changes.     

中国典型海相富有机质页岩的生气机理

目前页岩生烃的评价体系主要停留在静态条件下,忽略了成烃的动态过程,不能正确评价页岩原始的生烃潜力.采用生烃动力学模拟实验方法,分别对一个相对低成熟的典型海相富有机质页岩及其干酪根样品开展封闭体系和半开放体系下的人工熟化,并对熟化后的两个系列样品进行黄金管生气动力学模拟实验.对裂解产物中气态烃化合物、轻烃类化合物以及碳同位素开展了定量分析,结果表明,甲烷生成过程被划分为4个阶段,即生油（小于1.0% EayR_o）、凝析油生成（1.0%~1.% EayR_o）、湿气生成（1.%~2.2% EayR_o）和干气生成阶段（大于2.2% EayR_o）;页岩中甲烷的最大产率主要来自干酪根的初次裂解（占22.7%）、可排沥青（占7.6%）和残余沥青（占19.6%）的二次裂解;经过早期排烃作用的页岩样品仍有大量的可溶沥青,在高-过成熟阶段其可以与干酪根、不可溶沥青相互作用,成为晚期主要的页岩生气母质.      

Comparison of oil shales and kerogen concentrates by 13C nuclear magnetic resonance

Six oil shales and their kerogen concentrates have been studied using ¹³C CP/MAS NMR techniques to study the distribution of organic carbon species. It is found that if the aromatic and aliphatic regions are divided at about 80 or 100 ppm, the apparent aromaticities of a raw shale and its kerogen concentrate are in good agreement. The presence of oxygen-substituted carbons in the raw shales and their depletion in the kerogen concentrates are observed and discussed.     

Comparison of oil shales and kerogen concentrates by C nuclear magnetic resonance

Six oil shales and their kerogen concentrates have been studied using ¹³C CP/MAS NMR techniques to study the distribution of organic carbon species. It is found that if the aromatic and aliphatic regions are divided at about 80 or 100 ppm, the apparent aromaticities of a raw shale and its kerogen concentrate are in good agreement. The presence of oxygen-substituted carbons in the raw shales and their depletion in the kerogen concentrates are observed and discussed.     

Study of petroleum generation by pyrolysis—I. Pyrolysis experiments by Rock-Eval and assumption of molecular structural change of kerogen using13C-NMR

Green River shale (Type I kerogen), Yaamba shale (Type II kerogen) and Sarufutsu coal (Type III kerogen) were heated to various temperatures using Rock-Eval. The amount of hydrocarbons generated and weight loss by pyrolysis were measured to obtain a better understanding of petroleum generation. After the pyrolysis experiments, elemental analysis (C, H), vitrinite reflectance (%R_o) measurement, maceral observation, infrared spectroscopy (IR) and¹³C-NMR spectroscopy were carried out on the coal samples. Changes in H/C atomic ratio, IR and NMR spectra indicate that experiments by Rock-Eval resemble those of the natural evolution of kerogen. However, the petrographic changes of the coal show more similarity to coal liquefaction and coking than to natural coalification. Changes in the amount of generated hydrocarbons with increasing maturation show that Type II kerogen produces more hydrocarbons than does Type I when R_o does not exceed 1.1%. Petroleum generation curves for the three samples were concordant with trends in natural systems, and a conceptual model of petroleum generation curve classified into three types is proposed, namely (1) curve of total amount enerated, (2) curve of generation rate, and (3) curve of fluid composition. Changes of IR and NMR spectra after pyrolysis imply that generated hydrocarbons are derived from aliphatic C structures of kerogen macromolecules. Moreover, the difference in genetic potential between Type I and Type III reflects different amounts of aliphatic structures. Type I is assumed to have a simple assemblage (mainly polymethylene carbons), and Type III is assumed to have a more complex variety of structures that are responsible for the difference in generation rates between the two kerogen Types. A quantitative analysis of C species of various bond structure by¹³C-NMR confirms that petroleum generation is the process of bond cleavage of kerogen macromolecules; lower-energy bonds decrease at an earlier stage of reaction, while aromatic carbons with higher bond energies survive to form graphitic structure at postmature stages. Emphasis is placed on the idea that the most important and direct factor in petroleum generation is a change in the molecular structure of kerogen with increasing maturation. NMR and other methods providing information about molecular structures of kerogen will become strong tools for evaluating source rocks and sedimentary basins in the future.     

Relics of biolipids in kerogen of Cambrian Siberian Platform oil shale

Products of thermal cracking of kerogen of Lower-Middle Cambrian oil shale are studied by modern instrumental analytical methods (FTIR, gas chromatography, mass spectrometry, etc.). The analyses demonstrate that the geopolymer kerogen matrix inherited fragments of lipids synthesized by living organisms, including aliphatic fat acids, both free or bounded into glycerol esters, i.e., animal or vegetable fats. It is shown that vegetable pigments (carotenes and xanthophylls) play a crucial role in the formation of monocyclic structures (including molecular alkylbenzene, alkylphenol, and phenylalkane fragments) in kerogen. Since the studied kerogen is rich in esters, it is worth performing alkaline hydrolysis of its macromolecules (ester saponification) before their thermolysis, which inevitably distorts the initial structure of molecular skeletons.     

Biological markers from Green River kerogen decomposition

Isoprenoid and other carbon skeletons that are formed in living organisms and preserved essentially intact in ancient sediments are often called biological markers. The purpose of this paper is to develop improved methods of using isoprenoid hydrocarbons to relate petroleum or shale oil to its source rock. It is demonstrated that most, but not all, of the isoprenoid hydrocarbon structures are chemically bonded in kerogen (or to minerals) in Green River oil shale. The rate constant for thermally producing isoprenoid, cyclic, and aromatic hydrocarbons is substantially greater than for the bulk of shale oil. This may be related to the substantial quantity of CO₂ which is evolved coincident with the isoprenoid hydrocarbons but prior to substantial oil evolution. Although formation of isoprenoid alkenes is enhanced by rapid heating and high pyrolysis temperatures, the ratio of isoprenoid alkenes plus alkanes to normal alkenes plus alkanes is independent of heating rate. High-temperature laboratory pyrolysis experiments can thus be used to predict the distribution of aliphatic hydrocarbons in low temperature processes such as in situ shale oil production and perhaps petroleum formation. Finally, we demonstrate that significant variation in biological marker ratios occurs as a function of stratigraphy in the Green River formation. This information, combined with methods for measuring process yield from oil composition, enables one to relate time-dependent processing conditions to the corresponding time-dependent oil yield in a vertical modified-in situ retort even if there is a substantial and previously undetermined delay in drainage of shale oil from the retort.     

伦坡拉盆地渐新统丁青湖组油页岩特征及其地质意义

伦坡拉盆地丁青湖组油页岩呈北西-南东向断续分布,长约50 km,油页岩有18~22层,薄者0.10 m,厚者8.81 m,一般厚0.70~2.00 m。工业分析数据表明,油页岩属于高灰分、中低含油率、低发热量型。油页岩有机碳质量分数为2.40%~20.23%,平均值7.38%,丰度较高。干酪根镜检显示油页岩有机质类型为腐泥型（Ⅰ型）,镜质体反射率（R_o）值为0.43%~0.71%,平均值为0.52%,说明油页岩有机质处于未成熟-低成熟阶段。油页岩样品检测出丰富的正构烷烃、类异戊二烯烷烃、萜烷化合物和甾烷化合物。饱和烃色谱/质谱特征表明伦坡拉油页岩有机母质来源以水生浮游植物为主。通过生物标志物特征及野外地质观察,揭示了油页岩形成于一定盐度的缺氧还原半深湖-深湖环境。湖盆内各种水生浮游植物、藻类等为油页岩的形成提供了主要的有机母质来源,稳定的构造条件和缺氧的环境有利于有机质的堆积和保存。     

高磁场固态碳13核磁共振法研究干酪根的热降解成烃机理

用高磁场(75.46MH_Z)固态碳13核磁共振(NMR)波谱仪研究了抚顺油页岩在热降解模拟试验中干酪根的化学结构变化.为了消除旋转边带的干扰,在应用交叉极化与魔角自旋(CP/MAS)技术的同时,采用了Dixon TOSS技术,从而得到高分辨的波谱图。据此测定了热降解过程中干酪根各种碳结构组成的变化,计算了芳碳率、亚甲基基团平均碳原子数、环缩合指数等一系列干酪根的结构参数,并与干酪根的相对产油潜力相关联.发现干酪根的产油潜力直接与亚甲基基团的含量有关,而芳碳以及与芳碳相连的甲基碳则贡献甚微.文中还对干酪根的热降解成烃机理作了探讨。     

陆相烃源岩凝析油形成演化实验模拟特征

为了解陆相烃源岩在深埋过程中凝析油形成与演化特征,利用高温高压生烃模拟仪对辽河盆地西部凹陷曙13 井、马南603 井和东部凹陷桃10 井烃源岩样品进行了半封闭体系生烃模拟实验。实验结果显示,I 型有机质（曙13 井烃源岩样品） 总凝析油产率峰值为2.32 mg/g TOC,出现在镜质体反射率（VR） 1.76 %Ro,并以低分子量烃类物质为主要成分,可能表明I 型有机质凝析油主要通过液态烃二次裂解形成。II 型有机质（马南603 井烃源岩样品） 总凝析油产率峰值为2.28 mg/g TOC,该峰值出现在VR 为2.42 %Ro,明显晚于I 型有机质凝析油产率峰值,其成分以相对高分子量的烃类物质为主,其次为低分子量烃类物质。III 型有机质（桃10 井烃源岩样品） 凝析油总产率最低,产率峰值仅为0.92 mg/g TOC,可能表明III型有机质生成凝析油潜力较差。     

陆相烃源岩凝析油形成演化实验模拟特征

为了解陆相烃源岩在深埋过程中凝析油形成与演化特征，利用高温高压生烃模拟仪对辽河盆地西部凹陷曙13 井、马南603 井和东部凹陷桃10 井烃源岩样品进行了半封闭体系生烃模拟实验。实验结果显示，I 型有机质（曙13 井烃源岩样品） 总凝析油产率峰值为2.32 mg/g TOC，出现在镜质体反射率（VR） 1.76 %Ro，并以低分子量烃类物质为主要成分，可能表明I 型有机质凝析油主要通过液态烃二次裂解形成。II 型有机质（马南603 井烃源岩样品） 总凝析油产率峰值为2.28 mg/g TOC，该峰值出现在VR 为2.42 %Ro，明显晚于I 型有机质凝析油产率峰值，其成分以相对高分子量的烃类物质为主，其次为低分子量烃类物质。III 型有机质（桃10 井烃源岩样品） 凝析油总产率最低，产率峰值仅为0.92 mg/g TOC，可能表明III型有机质生成凝析油潜力较差。     

川东地区东岳庙段沉积环境演化及其页岩油气富集主控因素分析

川东地区下侏罗统自流井组东岳庙段富有机质泥页岩发育，且在局部地区已获工业页岩油气流，但尚未实现规模开发，其页岩油气富集机理研究滞后于生产实践。本文在野外调查和测试分析的基础上，对其沉积环境演化及页岩油气地质条件进行分析，并探讨其页岩油气富集主控因素，以期为实现东岳庙段页岩油气突破提供有益借鉴。结果显示：川东地区东岳庙段发育一个完整的水进水退沉积旋回，富有机质泥页岩主要发育于中部半深湖相，厚约15~30m，TOC平均为1.79%，以II型有机质为主，热演化程度较高，达凝析油—湿气阶段。以黏土矿物粒间孔和有机质孔为主，脆性矿物含量中等，脆性指数平均为62.1%。平均孔隙度为8.85%，而渗透率极低，均值仅0.239mD，呈现出“高孔低渗”特征，层内油气以侧向运移为主。其页岩油气的富集主要受富有机质泥页岩分布、热演化程度和裂缝发育条件的控制。推论垂向富有机质泥页岩连续发育的现今油气低势区是川东地区东岳庙段潜在的页岩油气高产区。     

The effect of oil expulsion or retention on further thermal degradation of kerogen at the high maturity stage: A pyrolysis study of type II kerogen from Pingliang shale,China

High maturity oil and gas are usually generated after primary oil expulsion from source rocks, especially from oil prone type I/II kerogen. However, the detailed impacts of oil expulsion, or retention in source rock on further thermal degradation of kerogen at the high maturity stage remain unknown. In the present study, we collected an Ordovician Pingliang shale sample containing type II kerogen. The kerogens, which had previously generated and expelled oil and those which had not, were prepared and pyrolyzed in a closed system, to observe oil expulsion or oil retention effects on later oil and gas generation from kerogen. The results show that oil expulsion and retention strongly impacts on further oil and gas generation in terms of both the amount and composition in the high maturity stage. Gas production will be reduced by 50% when the expulsion coefficient reaches 58%, and gas from oil-expelled kerogen (less oil retained) is much drier than that from fresh kerogen. The oil expulsion also causes n-alkanes and gas compounds to have heavier carbon isotopic compositions at high maturity stages. The enrichment of ¹³C in n-alkanes and gas hydrocarbons are 1‰ and 4–6‰ respectively, compared to fresh kerogen. Oil expulsion may act as open system opposite to the oil retention that influences the data pattern in crossplots of δ¹³C₂–δ¹³C₃ versus C₂/C₃, δ¹³C₂–δ¹³C₃ versus δ¹³C₁ and δ¹³C₁–δ¹³C₂ versus ln(C₁/C₂), which are widely used for identification of gas from kerogen cracking or oil cracking. These results suggest that the reserve estimation and gas/source correlation in deep burial basins should consider the proportion of oil retention to oil expulsion the source rocks have experienced.     

Parallel micropetrographic and chemical studies of the solid degradation products from stepwise alkaline permanganate oxidation of a kerogen concentrate

The usefulness of parallel micropetrographic and chemical investigations to illustrate the nature of kerogen is demonstrated from data obtained in the study of the Aleksinac shale (Yugoslavia). To obtain more information about the chemical nature of kerogen, the stepwise oxidation with alkaline permanganate reported earlier has been modified and supplemented with micropetrographic and chemical investigations of partially degraded kerogen concentrates isolated from each degradation step. Five different types of particles were observed in kerogen concentrates. The results both of micropetrographic and of chemical investigations indicate a heterogeneity of the Aleksinac shale kerogen and a different reactivity of the particles observed.     

湘西北地区寒武系牛蹄塘组页岩气资源前景

湘西北地区牛蹄塘组黑色页岩展布广泛,为寒武纪纽芬兰世—第二世滞留还原条件的沉积产物,适中的埋深和较大的厚度为其提供了良好的气藏条件。对其有机地化参数进行试验分析:TOC值为0.59%～13.05%,均值3.75%,有机质丰富;R_o值为1.87%～4.00%,均值3.05%,成熟度高;干酪根类型以Ⅰ型为主,少量为Ⅱ型,具有良好的生气潜力;矿物组成中脆性矿物含量为33%～87%,平均含量为68%,而黏土总量为13%～43%,平均为26%,脆性矿物/黏土矿物值高,有利于储层改造;页岩孔隙度为0.3%~8.0%,平均为3.3%,渗透率均小于0.04×10^-3μm²,为低孔低渗类型。综合研究表明,牛蹄塘组具有良好的页岩气生储潜力,同时运用条件概率体积法对其资源量进行评估计算,资源量十分可观。在此基础上对湘西北地区牛蹄塘组划分出6个页岩气有利区,为进一步实施页岩气勘查提供依据。     

Possible carotenoid-derived structures in fossil kerogens

The unique KMnO₄ degradation products of β-carotene, previously identified as 2,2-dimethyl succinic acid (C₆) and 2,2-dimethyl glutaric acid (C₇) have been found in the oxidation products of Green River shale (Eocene, 52 × 10⁶yr) and Tasmanian Tasmanite (Permian, 220−274 × 10⁶yr) kerogens. These two compounds were also detected in KMnO₄ degradation products of young kerogens from lacustrine and marine sediments. The results indicate that kerogens incorporated carotenoids (possibly β-carotene) at the time of kerogen formation in surface sediments. Both acids are useful markers to obtain information on biological precursors contributing to the formation of fossil kerogens.