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.     

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.     

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.     

Investigation of catalytic effects of indigenous minerals in the pyrolysis of Aleksinac oil shale organic matter

The catalytic effect of indigenous minerals in the pyrolysis of Aleksinac (Yugoslavia) oil shale was studied in this paper. The substrates were prepared by gradual removal of the mineral constituents (carbonates, silicates, pyrite) and the free and bound bitumens. The substrates were analyzed by chemical methods, X-ray diffraction, porosimetry, thermal analysis, ¹³C NMR, and standard ASTM Micro Activity Test (MAT) designed for the investigation of cracking catalysts. The liquid pyrolysis products were analyzed by organic geochemical techniques as well. Based on the yields of gaseous and liquid products and the coke, conversion degrees, GC analyses (MAT parameters) and weight losses (TG parameter), the catalytic effect of indigenous mineral components in the pyrolysis of Aleksinac oil shale organic matter was found to be very low. The results suggested that principal organic matter changes should be attributed to thermal rather than to catalytic cracking.     

海相烃源岩二次生烃潜力定量评价新方法

烃源岩二次生烃的演化过程是残余干酪根热解演化与残留油热裂解转化两个既相互联系又完全不同的物理化学反应过程的叠加。本文利用自制高压釜热压生烃模拟实验装置,采取分阶段连续递进模拟实验方式,以海相烃源岩样品为例分别评价了残余干酪根的生烃潜力与残留可溶有机质转化油气潜力,建立了一套不同起始与终止成熟度海相烃源岩二次生烃潜力的定量评价方法,并首次明确提出了干酪根生油指数KIo、干酪根生气指数KIg、干酪根生烃指数KIh等评价烃源岩生烃潜力的参数,弥补了ROCK EVAL热解评价方法无法分别评价烃源岩在不同生烃演化阶段所生成的“油”或“烃气”潜力的不足。     

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.     

Investigation of the pyrolytic liberation of molecular nitrogen from Palaeozoic sedimentary rocks

Open-system non-isothermal pyrolysis up to 1,200°C in combination with elemental analysis was used to study the thermal liberation of molecular nitrogen (N₂) from sedimentary rocks and kerogen concentrates of Palaeozoic age from the Central European Basin system and an Eocene shale (Liaohe Basin, China) with a high content (36%) of ammonium feldspar (buddingtonite). The N/C_org (atomic) ratios of the kerogen concentrates ranged from 0.005 to 0.014, which represents the range commonly observed for coals. Bulk N/C_org ratios of the Palaeozoic shales extended from 0.035 to 0.108, indicating the presence of significant amounts of inorganic nitrogen. Namurian A and A-B (CnA; CnA-B) samples typically exhibited the earliest onset of N₂ generation with intense, characteristic peaks around 600°C. N₂ liberation from the buddingtonite-rich sample occurred at higher temperatures, with a broad peak around 700°C. Pyrograms of the kerogen concentrates showed no or strongly reduced N₂ generation in the 500–700°C range. On-line isotope-specific analysis of the pyrolytically liberated N₂ on one sample revealed a variability of ∼10‰ in the δ¹⁵N values and a steady increase in δ¹⁵N with temperature during the main phase of N₂ generation.     

Distribution and geochemical significance of trace elements in shale rocks and their residual kerogens

There is a dearth of information about the distribution of trace elements in kerogen from shale rocks despite several reports on trace element composition in many shale samples. In this study, trace elements in shale rocks and their residual kerogens were determined by inductively coupled plasma–mass spectrometry. The results from this study show redox-sensitive elements relatively concentrated in the kerogens as compared to the shales. This may be primarily due to the adsorption and complexation ability of kerogen, which enables enrichment in Ni, Co, Cu, and Zn. For the rare earth elements (REEs), distinct distribution characteristics were observed for shales dominated by terrigenous minerals and their kerogen counterparts. However, shales with less input of terrigenous minerals showed similar REE distribution patterns to their residual kerogen. It is speculated that the distribution patterns of the REEs in shales and kerogens may be source-related.     

泥页岩热模拟实验及成岩演化模式

随着泥页岩油气勘探开发的不断推进,对泥页岩的成岩作用研究越来越受到重视。通过对三种不同干酪根类型的泥页岩样品的热模拟实验发现,随着有机质成熟度的增加,干酪根热解生烃产生的有机质孔及不稳定矿物溶蚀孔增加,是泥页岩储集空间增加的主要原因;泥页岩成岩作用类型主要有黏土矿物转化、不稳定矿物溶蚀作用和重结晶作用;结合镜质体反射率,建立了基于热模拟实验的泥页岩综合成岩演化模式。研究表明:不同类型的干酪根在生烃过程中演化特征不同,Ⅰ型干酪根以"解聚型"的途径生烃,以产生有机质边缘孔为主;Ⅲ型干酪根以"平行脱官能团型"的途径生烃,以产生有机质内部孔为主;Ⅱ型干酪根介于两者之间,既可以产生有机质内部孔,也可以产生有机质边缘孔。     

The granular and polymer composite nature of kerogen-rich shale

In the past decade, mechanical, physical, and chemical characterization of reservoir shale rocks, such as the Woodford shale, which is kerogen-rich shale (KRS), has moved toward micro- and nanoscale testing and analyses. Nanoindentation equipment is now widely used in many industrial and university laboratories to measure shale anisotropic Young’s moduli, kerogen stiffness, plastic yield parameters, and other isotropic and anisotropic poromechanical and viscoelastic properties. However, to date, failure analyses of KRS and the effects of organic components on the tensile strength have not been observed or measured at the micro- or nanoscales. In this study, preserved kerogen-rich Woodford shale samples manufactured in micro-beam and micro-pillar geometries were mechanically tested and brought to failure in tension and compression, respectively. These tests were conducted in situ using a nanoindenter inside a scanning electron microscope (SEM). The load versus displacement curves of prismatic micro-cantilever beams were analyzed in light of high-resolution images collected during tensile fracture initiation, propagation, and ultimately sample failure. The micro-pillar geometries were subjected to a uniaxial compressive load and were also brought to failure while capturing measurements of stress and strain. It was found that, within just a few hundred microns of the KRS micro-cantilever beams, both brittle and ductile failure modes were observed. In the ductile plastic domain, strain-softening and strain-hardening behaviors were identified and characterized. These were not due to confining stress variations, but due to the volume of the organic matter and the way it is interlaced with the shale minerals in and around the failure planes. The tensile strength characteristics and the large modulus of toughness of kerogen, which is a cross-linked polymer, definitely weigh heavily in our engineering field applications, such as hydraulic fracking, which is a Mode I tensile fracture opening and propagation phenomenon. This practice demands that, due to the complex composite nature of KRS, mechanical characterization be not only for unconfined compressive strength but also for unconfined tensile strength and moduli of ruptures. At the end of this study, the need for nanometer scale mechanical characterization of KRS will become apparent. These nano- and micro-scale shale failure tests reinforce our previous understanding of the heterogeneous composite nature of Woodford KRS and its complex behavior, as well as other source shale reservoir formations.     

Methane adsorption comparison of different thermal maturity kerogens in shale gas system

To determine the effect of thermal maturity on the methane sorption in shale gas system, two different thermal maturity kerogens of type II isolated from Barnett shale of Fort Worth Basin were used to measure the methane adsorption amount under the pressure ranging from 0 to 14 MPa at constant temperatures. One kerogen was called Lee C-5-1 with 0.58% of vitrinite reflectance; the other was called Blakely#1 kerogen with 2.01% of vitrinite reflectance. The results suggested that the methane sorption capacity of kerogen Blakely#1 was higher than the immature kerogen Lee C-5-1, and its Langmuir constant and Langmuir maximum sorption amount, which were reached by fitting the measured data for at least square method, greater than the immature kerogen Lee C-5-1. This may be associated with that nanopores opened up during the degradation of organic matter, and which increased the specific surface area of kerogen. Therefore, the over mature kerogen has greater methane adsorption capacity.     

页岩储层岩石物理模型及地震AVO响应模拟

通过模拟并分析各向异性页岩岩石物理模型,研究页岩中干酪根含量变化对页岩弹性各向异性的影响,其结果为应用AVO方法定量解释页岩储层厚度和干酪根含量提供依据。岩石物理模型预测了页岩速度和各向异性参数随干酪根含量的变化规律。应用传播矩阵方法计算薄层页岩的AVO响应,得到反射系数关于页岩层厚度、入射波频率、干酪根含量和入射角的函数。数值模拟结果表明:在干酪根含量不变且在同一入射角下的反射系数在频率域呈周期变化,该周期与薄层厚度成反比;对同一频率入射波和相同入射角,反射系数幅值随干酪根含量增加而变大。     

Apparent permeability and representative size of shale: a numerical study on the effects of organic matter

The impact of organic matter on the flow capacity of shale oil rocks is presumably significant, and the knowledge about the representative size is fundamental for the upscaling studies. The error of the experimentally determined permeability values is comparable with the contribution of kerogen to shale permeability, instead a 2D numerical model is employed to explore the normalised equivalent permeability and the representative elementary area (REA) of shale oil rocks in detail incorporating the effects of kerogen. The discussions on the normalised equivalent permeability and the REA are based on the statistical average and standard deviation from 1000 different runs, respectively. The inorganic permeability heterogeneity is introduced based on the assumption of a lognormal pore size distribution and the Monte Carlo sampling method. The effects of kerogen geometric characteristics are incorporated by putting forward several representative cases for comparison. The effects of the organic permeability contrast (ratio of permeability to the inorganic permeability with no heterogeneity), total organic carbon (TOC, volume fraction), inorganic permeability heterogeneity and kerogen geometric characteristics on the normalised equivalent permeability (ratio of the intrinsic equivalent permeability to inorganic permeability with no heterogeneity) and the REA are discussed comprehensively. This work can provide a better understanding of shale oil rocks at the micrometer scale.     

西澳大利亚珀斯盆地页岩气资源研究

珀斯盆地位于澳大利亚西海岸,是西澳大利亚页岩气资源勘探的重点区域。该盆地属于复杂的凹陷裂谷,海相沉积二叠纪的Carynginia组和早三叠世Kockatea页岩层被认为是潜在的含气地层。通过搜集大量外文文献,全面总结了该盆地含气目标层的地物化特征,Carynginia组的总有机碳含量为1%~15%,干酪根为III型,Ro在0.56~1.91;Kockatea页岩层的总有机碳含量为1%~4%,干酪根为II/III混合型,Ro为0.48~1.93。两组共划分了11各岩相段,其中黑色页岩岩相段和含黄铁矿泥岩段是最重要的生烃含气层。综合考虑地层、地化指标和岩石地球物理性质,圈出了可供参考的页岩气甜点区。     

Kerogen based characterization of major gas shales: Effects of kerogen fractionation

Research into the origin and the mode of entrapment and expulsion of natural gas from unconventional plays requires the isolation and separation of kerogen in its purest and most intact form from the rock matrix. This study expands on the comparative analysis of the effects that isolation methods, conservative closed system versus conventional open system, have on kerogen’s elemental, isotopic and physical properties. Four major gas shales, including the Barnett, the Marcellus, the Haynesville and a Polish gas shale, were chosen. In addition, the Monterey shale, though not strictly a gas shale, was included to address the effects on sulfur rich, Type II-S kerogen.Results indicate that the kerogen residues from the conventional open system method showed lower recovery and higher mineral content than those from the conservative closed system method. Differences were manifested in the elemental analysis data, where kerogens isolated using the open system method showed a significant deficit in the organic C, H, O, S and N material balance. Furthermore, the recovered residues show different sulfur content and δ³⁴S composition, most likely attributable to differences in pyrite content. Nevertheless, the relative abundances of the various macerals in the kerogen residues from the same parent shale are not very different; neither was the bulk δ¹³C composition of the recovered residues. This is not particularly surprising, considering that in all the five cases examined in this study, the organic matter was fairly homogeneous.     

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.      

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。     

临兴地区海陆过渡相页岩及页岩气地球化学特征

为揭示鄂尔多斯盆地东缘上古生界海陆过渡相页岩及页岩气地球化学特征,选取临兴地区页岩样,开展薄片鉴定、全岩和黏土含量、扫描电镜、有机碳、岩石热解、干酪根显微组分和干酪根碳同位素测试,分析页岩解吸气的气体组分和碳同位素组成。结果表明:临兴地区过渡相页岩矿物组分主要是石英和黏土矿物,含少量方解石、斜长石、钾长石、白云石和黄铁矿等。受矿物成因、沉积环境等多方面的影响,不同矿物组分与有机质赋存方式各异。石英与有机质存在2种赋存方式,黏土矿物存在3种赋存方式,黄铁矿存在4种赋存方式。有机质类型为Ⅱ₂–Ⅲ型,有机碳含量平均值大于2.0%,干酪根碳同位素介于–24.5‰~–23.2‰。镜质体反射率介于0.92%~1.30%,t_max值介于427~494℃,有机质热演化达到成熟阶段。页岩气中烃类气以甲烷为主,含有少量乙烷、丙烷,总体属于干气。甲烷碳同位素均值为–40.0‰,介于海相页岩气和陆相页岩气甲烷碳同位素之间;乙烷碳同位素值介于–26.8‰~–22.56‰,均大于–29‰,整体呈现出δ13C₁＜δ13C₂＜δ13C₃正碳序列。研究认为,该区页岩具备大量生成页岩气的潜力,页岩气主要来源于上古生界偏腐殖型页岩,属于由干酪根裂解而生成的有机热成因煤成气。      

Chemical structure and 13C NMR spectra of the kerogen of carbonaceous rock masses

The spectra of the kerogen from the Middle Volga oil shales of the Volga-Pechora shale province and from the Ukhta domanik’s carbonaceous deposits have been studied. In the Middle Volga and domanik kerogens, carbon-oxygen bonding types have been revealed as dominant. Significant distinctions between the two kerogen types have been established. The presence of oxygen in carbonyl and phenol groups is typical for the domanik kerogen, and also in ether bonds for the kerogen of the Middle Volga shale rock mass, which are of considerable importance in its structure.