Automated Kerogen Classification in Microscope Images of Dispersed Kerogen Preparation

We develop the classification part of a system that analyses transmitted light microscope images of dispersed kerogen preparation. The system automatically extracts kerogen pieces from the image and labels each piece as either inertinite or vitrinite. The image pre-processing analysis consists of background removal, identification of kerogen material, object segmentation, object extraction (individual images of pieces of kerogen) and feature calculation for each object. An expert palynologist was asked to label the objects into categories inertinite and vitrinite, which provided the ground truth for the classification experiment. Ten state-of-the-art classifiers and classifier ensembles were compared: Naïve Bayes, decision tree, nearest neighbour, the logistic classifier, multilayered perceptron (MLP), support vector machines (SVM), AdaBoost, Bagging, LogitBoost and Random Forest. The logistic classifier was singled out as the most accurate classifier, with an accuracy greater than 90. Using a 10 times 10-fold cross-validation provided within the Weka software, we found that the logistic classifier was significantly better than five classifiers (p<0.05) and indistinguishable from the other four classifiers. The initial set of 32 features was subsequently reduced to 6 features without compromising the classification accuracy. A further evaluation of the system alerted us to the possible sensitivity of the classification to the ground truth that might vary from one human expert to another. The analysis also revealed that the logistic classifier made most of the correct classifications with a high certainty.     

贵州中三叠统烂泥沟金矿有机质的初步研究

烂泥沟金矿是以浊积岩为容矿岩石的微细浸染型金矿。有机岩石学分析表明,矿石与围岩中干酪根类型无明显差别,同属腐泥-腐植型。与围岩相比,矿石中干酪根成熟度(R₀=2.74%-3.06%)和含金性(6.15-24.8μg/g)均较高;干酪根总含金量在全岩中所占的比例是围岩高于矿石。氯仿沥青“A”的检测说明,矿石样品中可溶性有机质形成于强还原和高盐度环境,沥青质和含硫有机化合物发育。研究认为,干酪根含金性与碳的活化有关;不饱和的有机基因对金的动一定转换可能具有重要意义。     

ESR assessment of kerogen maturation and its relation with petroleum genesis

Petroleum hydrocarbons are formed by breakdown of kerogen preserved in source rocks throughout the process of catagenesis. This process is accompanied by free radical generation in kerogen. The availability of measuring free radicals in kerogen using ESR to deduce a maturation estimation of potential source rocks has been hindered due to the presence of the solvent-extractable organic molecules (SEOM) trapped within the kerogen matrix. Spin concentration (Ns) of the kerogen treated with pyridine (K_Py) represents the paramagnetic centers of the kerogen matrix itself and provides a potential parameter to evaluate kerogen maturation.     

Organic geochemistry of marine source rocks and pyrobitumen-containing reservoir rocks of the Sichuan Basin and neighbouring areas,SW China

Three bitumen fractions were obtained and systematically analysed for the terpane and sterane composition from 30 Paleozoic source rocks and 64 bitumen-containing reservoir rocks within the Upper Sinian, Lower Cambrian, Lower Silurian, Middle Carboniferous, Upper Permian and Lower Triassic strata in the Sichuan Basin and neighbouring areas, China. These bitumen fractions include extractable oils (bitumen I), oil-bearing fluid inclusions and/or closely associated components with the kerogen or pyrobitumen/mineral matrix, released during kerogen or pyrobitumen isolation and demineralization (bitumen II), and bound compounds within the kerogen or pyrobitumen released by confined pyrolysis (bitumen III). In addition, atomic H/C and O/C ratios and carbon isotopic compositions of kerogen and pyrobitumen from some of the samples were measured. Geochemical results and geological information suggest that: (1) in the Central Sichuan Basin, hydrocarbon gases in reservoirs within the fourth section of the Upper Sinian Dengying Formation were derived from both the Lower Cambrian and Upper Sinian source rocks; and (2) in the Eastern Sichuan Basin, hydrocarbon gases in Middle Carboniferous Huanglong Formation reservoirs were mainly derived from Lower Silurian source rocks, while those in Upper Permian and Lower Triassic reservoirs were mainly derived from both Upper Permian and Lower Silurian marine source rocks. For both the source and reservoir rocks, bitumen III fractions generally show relatively lower maturity near the peak oil generation stage, while the other two bitumen fractions show very high maturities based on terpane and sterane distributions. Tricyclic terpanes evolved from the distribution pattern C₂₀ < C₂₁ < C₂₃, through C₂₀ < C₂₁ > C₂₃, finally to C₂₀ > C₂₁ > C₂₃ during severe thermal stress. The concentration of C₃₀ diahopane in bitumen III (the bound components released from confined pyrolysis) is substantially lower than in the other two bitumen fractions for four terrigenous Upper Permian source rocks, demonstrating that this compound originated from free hopanoid precursors, rather than hopanoids bound to the kerogen.     

Methodological comparison for quantitative analysis of fossil and recently derived carbon in mine soils with high content of aliphatic kerogen

In mine soil, quantification of soil organic carbon (OC) derived recently from biomass decomposition is complicated by the presence of fossil (geogenic) C derived from coal, oil shale, or similar material in the overburden. The only reliable method for such measurement is ¹⁴C analysis (i.e. radiocarbon dating) using instrumentation such as accelerator mass spectrometry, which is too expensive for routine laboratory analysis. We tested two previously used and two new methods for recent C quantification and compared them with ¹⁴C AMS radiocarbon dating as a reference using a set of soil samples (n = 14) from Sokolov, Czech Republic: (i) ¹³C isotope ratio composition, (ii) cross polarization magic angle spinning ¹³C nuclear magnetic resonance (CPMAS ¹³C NMR) spectroscopy, (iii) near infrared spectroscopy (NIRS) coupled with partial least squares regression and (iv) Rock–Eval pyrolysis. Conventional methods for OC determination (dry combustion, wet dichromate oxidation, loss-on-ignition) were also compared to quantify any bias connected with their use. All the methods provided acceptable recent carbon estimates in the presence of mostly aliphatic fossil C from kerogen. However, the most accurate predictions were obtained with two approaches using Rock–Eval pyrolysis parameters as predictors, namely (i) S₂ curve components and (ii) oxygen index (OI). The S₂ curve approach is based on the lower thermal stability of recent vs. fossil organic matter. The OI approach corresponded well with ¹³C NMR spectra, which showed that samples rich in recent C were richer in carboxyl C and O-alkyl C. These two methods showed the greatest potential as routine methods for recent C quantification.     

油气无机成因学说的新进展

介绍了油气无机成因学说的新发展,主要是目前在西方、俄罗斯等影响较大的关于无机生油气的几个学派以及在中国的一些学派。其中之一是Ｇｏｌｄ氏的地幔脱气理论,之二是费－托地质合成理论。     

Petroleum retention in the Mandal Formation,Central Graben,Norway

Upper Jurassic organic matter-rich, marine shales of the Mandal Formation have charged major petroleum accumulations in the North Sea Central Graben including the giant Ekofisk field which straddles the graben axis. Recent exploration of marginal basin positions such as the Mandal High area or the Søgne Basin has been less successful, raising the question as to whether charging is an issue, possibly related to high thermal stability of the source organic matter or delayed expulsion from source to carrier.The Mandal Formation is in part a very prolific source rock containing mainly Type II organic matter with <12 wt.-% TOC and HI < 645 mg HC/g TOC but Type III-influenced organofacies are also present. The formation is therefore to varying degrees heterogeneous. Here we show, using geochemical mass balance modelling, that the petroleum expulsion efficiency of the Mandal Formation is relatively low as compared to the Upper Jurassic Draupne Formation, the major source rock in the Viking Graben system. Using maturity series of different initial source quality from structurally distinct regions and encompassing depositional environments from proximal to distal facies, we have examined the relationship between free hydrocarbon retention and organic matter structure. The aromaticity of the original and matured petroleum precursors in the Mandal source rock plays a major role in its gas retention capacity as cross-linked monoaromatic rings act on the outer surface of kerogen as sorptive sites. However, oil retention is a function of both kerogen and involatile bitumen compositions. Slight variations in total petroleum retention capacities within the same kerogen yields suggest that texture of organic matter (e.g. organic porosity) could play a role as well.     

Sensitivity of the elastic anisotropy and seismic reflection amplitude of the Eagle Ford Shale to the presence of kerogen

The Eagle Ford Shale of Central and South Texas is currently of great interest for oil and gas exploration and production. Laboratory studies show that the Eagle Ford Shale is anisotropic, with a correlation between anisotropy and total organic carbon. Organic materials are usually more compliant than other minerals present in organic‐rich shales, and their shapes and distribution are usually anisotropic. This makes organic materials an important source of anisotropy in organic‐rich shales. Neglecting shale anisotropy may lead to incorrect estimates of rock and fluid properties derived from inversion of amplitude versus offset seismic data. Organic materials have a significant effect on the PP and PS reflection amplitudes from the Austin Chalk/Upper Eagle Ford interface, the Upper Eagle Ford/Lower Eagle Ford interface, and the Lower Eagle Ford/Buda Limestone interface. The higher kerogen content of the Lower Eagle Ford compared with that of the Upper Eagle Ford leads to a negative PP reflection amplitude that dims with offset, whereas the PS reflection coefficient increases in magnitude with increasing offset. The PP and PS reflection coefficients at the Austin Chalk/Upper Eagle Ford interface, the Upper Eagle Ford/Lower Eagle Ford interface, and the Lower Eagle Ford/Buda Limestone interface all increase in magnitude with increasing volume fraction of kerogen.     

煤和干酪根纳米结构的研究进展

对煤和干酪根结构的认识得益于技术和方法的不断创新。基于各种方法,先后建立了多个煤和干酪根的结构模型,但至今没有得到普遍认可。原子力显微镜(AFM)可以实时、实空间、原位成像,可以观察单个原子层的局部表面结构,直接观察表面缺陷、表面重构、表面吸附体的形态和位置以及表面扩散等动态过程。在对图像的分析中,AFM超越了传统仪器单纯平面成像的功能,可提供样品表面动态三维图像和用于分析的定量化信息。通过纳米技术,实现了原子级的分辨率的观察,揭示了煤和干酪根聚集态分子和纳米级孔隙的形态、大小、结构及相互间的空间排列特征,显示出在煤和干酪根结构研究中的巨大潜力。纳米技术为煤和干酪根结构的基础研究工作拓展了新的途径,也为非常规油气的勘探开发和煤炭的二次转化研究提供了科学依据。     

Tmax of asphaltenes: a parameter for oil maturity assessment

A new maturity parameter determined on both oil and bitumen samples, the asphaltene T_max, is proposed and discussed. This parameter could be very useful to address the maturity of the source rock. The asphaltene T_max is measured by programmed Rock-Eval pyrolysis, using a modified temperature program. Some phases of the experimental procedure, such as the asphaltene preparation and the Rock-Eval measurement substratum choice, are crucial in order to achieve reliable data. Laboratory simulations were carried out in order to assess the possible effects of both primary and secondary migration on asphaltene T_maxin the expelled oil: the original value of the asphaltene T_max in the bitumen is not substantially modified and it is very close to that measured on kerogen. Examples of the determination of asphaltene T_max on many samples, collected from different areas and with different organic matter composition, are given. Results show that T_max values from oil asphaltenes are reasonable indicators of source rock maturity.