Coalification in Carboniferous sediments from the Lötschberg base tunnel

Vitrinite reflectance (Rr), proximate analysis and carbon isotope composition (δ¹³C) have been used to characterise coal samples from two zones of Late Carboniferous sediments (Gastern and Ferden) in the Aar massif where they are penetrated by the Lötschberg base tunnel (constructed between 1999 and 2005). Samples are characterised by variable ash yields (21.7–93.9%; dry basis); those with ash yields of less than ~50% and with volatile matter content (V;dry ash-free basis) within the limits 2 < V% ≤ 8 are anthracite. Values of Rr range from 3.89% to 5.17% and indicate coalification to the rank of anthracite and meta-anthracite in both Gastern and Ferden Carboniferous zones. Samples of anthracite and shale from the Gastern Carboniferous exhibit a relatively small range in δ¹³C values (–24.52‰ to –23.38‰; mean: –23.86‰) and are lighter than anthracite samples from the Ferden Carboniferous (mean: –22.20‰). The degree of coalification in the Gastern and Ferden Carboniferous zones primarily depends on the maximum rock temperature (T) attained as a result of burial heating. Vitrinite reflectance based estimates of T range from ~290° –360 °C. For a proposed palaeogeothemal gradient of 25 ° C/km at the time of maximum coalification the required overburden is attributable to relatively thin autochtonous Mesozoic/Cenozoic sedimentary cover of the Aar massif and Gastern granite and deep tectonic burial beneath advancing Helvetic, Ultrahelvetic and Prealpine (Penninic) nappes in Early Oligocene to Miocene.     

早期煤化作用机制与有机质早期成烃演化

近年来，未熟和低熟油气田的发现、生物气藏的勘探和开发，极大地促进了对有机质早期转变的研究；而有机质早期转变机制的正确认识对于煤和干酪根中显微组分的成因、后期热演化都有着重要的影响。对早期煤化作用机制和有机质早期成烃作用的研究现状、进展及存在的问题进行了综述。     

东秦岭北缘煤的变质作用与板块构造的关系

以河南省东秦岭造山带北缘山西组二１煤层的煤岩、煤质、煤有机地球化学和“晶核”结构的综合研究为前提，结合板块构造和地球物理场的研究分析，认为该区二１煤的变质热源主要与长期复杂的板块俯冲、Ａ型碰撞所引起的地壳结构调整而使前陆盆地区岩石圈结构变化，大地热流急增的结果有关。二１煤的变质主要经历了早期（印支期前）的区域深成变质（达肥－气煤）和后期（印支－燕山期）的典型异常热变质作用（达无烟煤－高阶无烟煤）。     

Chemistry of alkali extraction of brown coals—I. Kinetics, characterisation and implications to coalification

Three Australian brown coals have been separated into humin and humic acid fractions and studied by high resolution solid state ¹³C NMR spectroscopy and Fourier transform IR spectroscopy. The aromatic rings of the humic acids are highly substituted showing that extensive cross linking must have occurred during formation from wood lignin and tannin. However, the humins contain more aliphatic carbon and hydrogen than the corresponding humic acids. This shows that little cross linking has occurred with other components of the brown coal such as resins, waxes cutin and algal detritus, and cross linking has not rendered the aromatics alkali insoluble. The kinetics of extraction are complex and not simple first order. This is reflected in the chemical composition of the humic acid which is extraction temperature dependent. We also observed that there is a conversion of aromatic carbon to aliphatic carbon and gas during extraction, probably by alkaline oxidation, resulting in ring opening. A range of suitable model compounds have been studied to confirm this finding. Such a mechanism may account for the modification of lignin in oxidising environments such as those occurring in the initial stages of coalification (lignite or brown coal formation) and in soils.     

构造物理化学条件对煤变质作用的控制

煤是对温度和压力等地质因素十分敏感的有机岩,各种构造-热事件控制下的物理化学条件,是促进煤岩演化的根本动力。本文对煤变质作用过程的研究现状进行了综述,着重讨论了煤岩在高煤阶-石墨演化阶段的控制因素、演化过程和演化机制。煤变质作用包括煤化作用阶段和石墨化作用阶段,共同构成一个连续的有机质演化过程,总体趋势是分子结构有序化、化学成分单一化,最终演变为以碳元素为主、三维有序结构的石墨。温度和压力(应力)是控制煤变质作用两大因素,在不同的演化阶段,这两大因素所起的作用和演变机理都有所差异。在低、中煤阶演化阶段,温度是煤化学结构演化的主要控制因素,为化学键断裂提供活化能,应力缩聚和应力降解则对煤化学结构演化具有催化作用。高煤阶-石墨化阶段的主要机制是导致基本结构单元BSUs之间相互联结使短程有序化范围增大的拼叠作用,构造应力在其中起到关键作用,BSUs定向和面网间距不断减小,促进大分子物理结构演化。加强煤变质作用的高级阶段-石墨演化过程的研究,将丰富和深化对煤-石墨物理化学结构完整演化序列的认识。煤系石墨成矿机制的高温高压模拟实验,则为煤变质作用构造物理化学条件研究提供了可行的技术手段。     

煤变质作用研究

本文从4个方面扼要地讨论了煤变质作用的近期进展。在煤级参数方面对镜质体反射率及其缺点和弥补的方法做了介绍,简述了近来提出的新的煤级参数。在煤化作用机理与特点方面概述了涉及煤化作用的煤结构研究新进展及其在煤化过程的演变中与镜质体反射率、挥发份的内在联系;煤化作用跃变与沥青化作用;“惰性组的煤化径迹”——煤化作用的一个新的方面。新的煤变质作用类型探讨。煤变质因素和煤化作用平衡,煤变质作用研究应用于其它地质学科。最后提出了应进一步研究的煤变质问题。     

再论煤中大分子基本结构单元演化的拼叠作用

芳构化作用和环缩合作用的传统煤化作用理论具有一定局限性,煤中基本结构单元拼叠作用是高煤级煤演化的特有机理。拼叠作用显著发生的起点位于镜质组最大反射率Ro,max为6．0％附近,大分子化学键的均裂提供了拼叠作用得以实现的微化学环境条件,其实质是一种“动力化学”过程,与氧接芳碳等有关的大量“均裂”是在短暂的煤化阶段中突然出现的,导致“拼叠作用”的显著发生具有“阶跃式”特征,是造成高煤级煤中期到后期阶段大分子基本结构单元急剧增大的根本原因和主要地球化学机理。     

郑庄区块煤层气赋存特征及控气地质因素

沁水盆地南部郑庄区块煤层气资源条件良好,勘探开发潜力大。通过对郑庄区块煤层气地质条件和储层条件的深入分析,认为本区煤层气赋存条件良好,含气量较高,储层吸附/解吸能力较好,但储层渗透率相对较低;郑庄区块煤层气藏主要受3类地质因素控制:构造对煤层气含量和赋存规律具有明显的控制作用;水文地质条件对煤层气具明显的水力封闭作用,该区地下水径流较弱,为典型的等势面扇状缓流型,有利于区块内煤层气的富集;燕山晚期岩浆活动和高异常地热场对煤层热演化和煤层气生成有显著的控制作用。      

煤层气系统——一种非常规含油气系统

为了更加有效地预测煤层气分布,指出煤层气有利勘探区域,引入了含油气系统来研究煤层气。煤层气系统是由煤层和其中的煤层气及煤层气藏形成所必需的一切地质要素和作用所组成的天然系统,其中的地质要素包括煤层及其顶底板,作用是煤层气的生成、储集和保存等。煤层气系统的建立和研究,为煤层气的勘探和开发提供了一种新的思维方式和研究方法,以及一套煤层气勘探研究的程序和框架。      

Chemical structural models for coalified wood (vitrinite) in low rank coal

Examination of a series of coalified gymnospermous woods ranging in rank from brown coal to subbituminous coal by solid-state ¹³C NMR and analytical pyrolysis has provided sufficient information to construct structural models depicting the changes that occur to lignin, the primary precursor of vitrinite, during coalification. Progressive changes in the chemistry of coalified wood suggest the following series of reactions: (1) demethylation to form catechol-like structures that are dominant components of brown coal and lignite A; (2) cleavage of aryl ether linkages to form phenols and reactive carbocations that alkylate the catechol rings; (3) dehydration of the catechol rings; (3) dehydration of the catechol-like structures to form the structures of subbituminous coal dominated by alkylphenols; and (4) reduction of the 3-carbon alkyl side chain derived from lignin to form propyl substituents. The models developed for each stage of coalification are derived from chemical modifications of the structure of lignin.