第六讲 控制煤成气藏形成的条件和因素

近年来的研究成果表明,含煤岩系不仅可形成天然气,也可形成石油。煤成油气的事实说明含煤盆地和含油气盆地有着内在的成生联系。即在一定条件下含煤盆地可以演化为含油气盆地;含煤岩系可以转化为油气源岩,并可形成一定规模的石油和天然气矿藏。      

中国侏罗系煤成油若干问题

在阐述了煤成油的概念，总结和评述了煤生油显微组分，生油门限，生油范围和生油高峰等问题后，本文通过吐哈等盆地侏罗系煤生油显微组分组成特征，可溶有机质演化，成熟度和有机质丰度，油源及原油成熟度对比；含煤岩系中煤层和泥岩的厚度及总量和煤及泥岩最高沥青和总烃转化率的对比； 其族组成和煤成原油的族组成特征的对比，提出了中国侏罗系煤成油盆地中泥岩比煤层对煤成油田形成有大的贡献看法。     

煤成气讲座 第六讲 控制煤成气藏形成的条件和因素

一、形成的基本因素近年来的研究成果表明,含煤岩系不仅可形成天然气,也可形成石油。煤成油气的事实说明含煤盆地和含油气盆地有着内在的成生联系。即在一定条件下含煤盆地可以演化为含油气盆地;含煤岩系可以转化为油气源岩,并可形成一定规模的石油和天然气矿     

中国煤成油研究进展和展望

中国煤和含煤岩系内石油的发现是在５０￣６０年代，而提出应在我国进行煤和含煤岩成油问题的研究是８０年代初，自提出煤成油问题以来短短的十余年时间里，不仅在有机岩石学，煤成油地球化学，热模拟实验和煤成油综合研究等煤和含煤岩系成油理论上取得了进展，而且在油勘探的实践上，在吐鲁番和彩南取得了重要的进展。     

煤造石油与煤成油理论关系研究进展综述

综述了煤造石油的研究进展。煤加氢液化研究结果表明挥发分、Ｈ与Ｃ比值、煤级、催化剂是影响煤炭液化的重要因素;对煤造石油与石油玩机成因说、煤造石油与煤一理论之间的联系进行了评述,现代含煤岩系煤成油研究得出的结论与煤造石油实践得出的结果近似一致,一些大油田分布带与大构造活动区带近于一致,由此使人们得出了类似于Ｆ－Ｔ法合成的石油无机成因理论。     

鄂尔多斯盆地叠合演化及构造对成煤作用的控制

鄂尔多斯盆地是多期成煤盆地叠合改造形成的构造盆地。石炭纪、二叠纪、三叠纪和侏罗纪成煤盆地的沉积演化过程具有一定差异,但煤炭资源形成的时空规律具有高度相似性。大地构造背景转换过程控制聚煤期,石炭纪、二叠纪含煤岩系形成于加里东—海西构造运动转换过程,三叠纪和侏罗纪含煤岩系形成于印支—燕山转换过程。沉积作用转换区域控制成煤区,在近海型盆地中,成煤区位于向陆一侧的河-海沉积作用转换区域。在内陆湖泊型盆地中,成煤区位于围绕湖心呈环带状分布的河-湖沉积作用转换区域。燕山及以后的构造运动控制了含煤岩系的形变方式和煤炭资源赋存状态。鄂尔多斯成煤盆地后期改造的显著特点是西部逆冲,东部隆起,南部和北部隆升和断陷共生。盆地西缘发育近南北向逆冲推覆构造,导致侏罗纪含煤岩系大面积剥蚀,造成石炭纪、二叠纪含煤岩系剥蚀、重复、褶皱和断裂。东部发生大面积隆起,石炭纪、二叠纪和侏罗纪含煤岩系遭受大范围剥蚀。盆地内部形成向北西缓倾的斜坡和南北向延伸的向斜,使晚古生代、三叠纪、侏罗纪煤炭资源得到保存。南部和北部边缘相继发生先抬升后断陷,形成了银川—河套断陷和汾渭断陷,构成了鄂尔多斯盆地含煤岩系的南北边界。构造背景和沉积作用转换是控制煤炭资源形成的重要地质条件,在大地构造运动界面上覆岩系中,寻找沉积体系转换区域是战略性找煤的有效途径。     

含煤盆地转化为含煤-含气(油)盆地的构造地质环境

与含煤岩系相关大气田的开发是中国天然气储产量快速增长的主体,为了进一步阐明与含煤岩系相关大气田的勘探前景,在概述了已发现大气田分布特征的基础上,用实例总结了含煤-含气(油)盆地形成条件,明确指出虽然不同类型含煤盆地发展演化的构造地质环境不完全相同,但是所有含煤盆地能否转化成为含煤-含气(油)盆地的关键因素是相同的,即:含煤岩系沉积期间和含煤岩系沉积后是否以沉降为主,沉积期间及沉积后所经历的构造地质作用能否有效匹配.上述构造地质环境持续时间越长,各种构造地质作用有效匹配程度越好,越利于转化成为含煤-含气(油)盆地,越有利于形成大型气田.中国特定的构造地质环境决定了含煤岩系是中国最重要的气源岩,一些大中型含煤盆地是构造地质环境最优越的盆地,还有较大勘探潜力,仍然可以继续发现更多的大型煤成气田,是未来相当长一段时间内中国天然气产量持续快速增长的主要勘探方向.      

煤和含煤岩系中潜在的共伴生矿产资源——一个值得重视的问题

煤是一种具有高度还原障和吸附障性能的有机岩和矿产,在特定的地质条件下,可以富集一些有益金属元素,并达到成矿的规模。综合国内外一些研究资料,论述了煤和含煤岩系中有益金属铌、镓、铼、钪的丰度、赋存状态、地质成因以及利用的可能性。煤中稀有金属元素富集或成矿的研究,是煤地球化学和矿床地球化学重要内容之一,值得进一步加强。     

“煤成油”—能源勘探的一个新领域

含煤地层中以腐殖型有机质为主的成煤物质在成煤过程中、特别是在沥青化过程中形成的“煤成油”已经成为能源勘探中的具有极大吸引力的一个重要方向。我国的油田多为陆相成因,属高含蜡质油,含油岩系与煤系共生或有密切关系。“煤成烃”理论,尤其是“煤成油”理论无论在理论上或实践中都存在许多需要解决的问题。“煤成油”理论所涉及的问题综其根本不外三个主要方面:一是煤及煤的各组成部分的成油能力和鉴定特征;二是形成物的运移,特别指的是初次运移;三是烃源对比和源源对比。而实用意义则在于对煤成油分布规律的研究和对开发的经济可行性的评价。     

煤源岩孔隙演化与煤成油气初次运移研究

通过加水热模拟实验对一褐煤样的生烃特征进行了研究,并利用压汞法研究了在热演化过程中煤源岩孔隙结构变化特征。结果表明煤源岩热解产物的形成和煤成油气初次运移与煤源岩孔隙结构之间有着密切的关系。在低温阶段,煤源岩中出现了较多的大孔隙和裂隙,此时主要是液态产物形成和排驱运移;在高温阶段,煤源岩大孔隙和裂隙消失而微小孔隙大量形成,此时主要是热解气大量形成和排驱运移。     

瓦窑堡煤系有机岩石学特征及煤成烃潜力研究

瓦窑堡煤系是我国重要的含煤岩系之一,陆相生油的观点最早可能源于瓦窑堡煤系含油性特征。通过对瓦窑堡煤系煤和暗色泥岩有机质的显微岩石学和宏观煤岩学特征的分析,提出了瓦窑堡煤系煤主要形成于深覆水森林泥炭沼泽相,类脂组含量高,且镜质组的主要类型为富氢的基质镜质体,有机地球化学结果表明瓦窑堡煤系煤具有Ⅱ型有机质的特征,处于低熟-成熟阶段,热模拟实验证明其具有良好的油气生成潜力。但由于瓦窑堡煤系规模小,煤层厚度薄,煤系泥岩有机质类型偏差,且煤中主要生油显微组分尚末进入大量生油期,因此难以形成油藏。     

Coal as a source rock for oil: a review

The geological debate about whether, and to what extent, humic coals have sourced oil is likely to continue for some time, despite some important advances in our knowledge of the processes involved. It is clear that not only liptinites, but also perhydrous vitrinites have the potential to generate hydrocarbon liquids in the course of natural coalification. Some liptinites, especially alginite, cutinite, and suberinite, contain a higher proportion of aliphatic moieties in their structure than other liptinites such as sporinite and resinite and are, therefore, more oil-prone. It is of potential value to be able to predict the several environments of deposition in which coals with high liptinite contents or containing perhydrous vitrinites may have been formed. Review of the distribution of oil-prone coals in time and space reveals that most are Jurassic–Tertiary with key examples from Australia, New Zealand, and Indonesia. Methods based both on experimental simulations and the examination of naturally matured samples have been used to determine the order of generation of hydrocarbons from different macerals. Results are not entirely consistent among the different approaches, and there is much overlap in the ranges of degradation, but it seems probable that in the natural environment vitrinites begin to generate early, followed by labile liptinites such as suberinite, then cutinite, sporinite, and, finally, alginite.Petroleum potential may be determined by experimental simulation of natural coalification or inferred through various micro-techniques, especially fluorescence and infrared (IR) spectroscopy, or bulk techniques such as elemental analysis and ¹³C NMR spectroscopy. The latter three techniques enable a measure of the polymethylene component of the coal, which now appears to be one of the best available approaches for determining petroleum potential. No method of experimental simulation of petroleum generation from coals is without criticism, and comparative results are highly variable. However, hydrous pyrolysis, confined pyrolysis, and forms of open-system hydrous pyrolysis approach acceptable simulations.Whether, and to what degree generated liquid hydrocarbons are expelled, has long been the central problem in ‘oil from coal’ studies. The structure of vitrinite was believed until recently to contain an interconnected microporous network in which generated oil would be contained until an expulsion threshold was attained. Recent studies show the pores are not interconnected. Combined with a dynamic model of pore generation, it now seems that expulsion of hydrocarbons is best explained by activated diffusion of molecules to maceral boundaries and ultimately by cleats and fractures to coal seam boundaries. The main reason for poor expulsion is the adsorption of oil on the organic macromolecule, which may be overcome (1) if coals are thin and interbedded with clastic sediments, or (2) if the coals are very hydrogen-rich and generate large quantities of oil.The existence of oil in vitrinite is attested to by solvent extractions, fluorescence properties, and by microscopic observations of oil and bitumen. Experimental simulation of expulsion of oil from coals has only recently been attempted. The relative timing of release of generated CO₂ and CH₄ could have considerable importance in promoting the expulsion of liquid hydrocarbons but the mechanism is unclear. As it is universally agreed that dispersed organic matter (DOM) in some shales readily generates and expels petroleum, it is curious that few consistent geochemical differences have been found between coal macerals and DOM in interbedded shales.Unambiguous evidence of expulsion from coals is limited, and in particular only a few commercial oil discoveries can be confidently correlated to coals. These include Upper Cretaceous Fruitland Formation coals in the USA, from which oil is produced; New Zealand Tertiary coals; and Middle Jurassic coals from the Danish North Sea. It is likely that coals have at least contributed to significant oil discoveries in the Gippsland Basin, Australia; in the Turpan Basin, China; and in the Kutei and Ardjuna basins in Indonesia, but this remains unproven. Early reports that early Jurassic coals in mid-Norway were a major source of the reservoired oils have been shown to be inaccurate.None of the proposed ‘rules of thumb’ for generation or expulsion of petroleum from coals seem particularly robust. Decisions on whether a particular coal is likely to have been an active source for oil should consider all available geological and geochemical information. The assumptions made in computational models should be well understood as it is likely with new understandings of processes involved that some of these assumptions will be difficult to sustain.     

煤和煤系泥岩生油能力再评价

煤和分散有机质（煤系泥岩或页岩）对煤成油田的贡献大小一直没有获得统一认识,这导致煤是否具有生排油能力直到现在仍然争论不休。选择了两个典型侏罗系煤和一个煤系泥岩样品,分别进行了限定体系热解生烃模拟,结果表明热解特征较差的泥岩（H／C 0．77,IH 146mg／g）却比中等富氢煤（H／C 0．82,IH 260mg／g）的生油量高出2．7倍,是一般煤（H／C 0．75,IH 199mg／g）生油潜力的6倍。这暗示着在煤成油评价中,不能简单把煤和煤系分散有机质对等进行评价,不然会低估煤系相对分散有机质的贡献而过高估计了煤的作用。热解模拟结果与吐哈盆地台北凹陷煤系岩石中有机质含量对比结果表明,该凹陷煤成油更可能来自于煤系泥岩而不是煤本身。此外,通过分析发现煤中液态烃稳定性较差,一般在低熟阶段就开始裂解生气,因此,被国内外学者普遍采纳的,IH（或S1）随成熟度变化的趋势不能作为判断煤排油门限的有效参考。     

煤层中菌藻生物及其成烃能力研究

通过对我国不同时代，不同产地煤层中菌藻生物化石的种类和丰度研究，观察到煤层中的菌藻类生物具形态各异，属种繁多，数量丰富的特征。经热模拟实验证明：菌藻类煤的成烃能力比同煤级的腐植煤高，（甲烷高1－2倍，液态烃高4－5倍），尤其对深水区形成的腐泥煤，是石油的主要母质。因此，今后在寻找煤层气或煤成油的有利区块时，应深入的研究成煤环境和成煤物质。     

生油煤形成的环境制约

通过对不同沉积环境下形成煤系源岩生烃潜力的对比研究，揭示出成煤古环境对煤成烃生成具有控制作用，并根据煤系源岩中赋存大分子有机质裂解产物分子的组成特征，提出了识别有利成烃煤相的分子有机地球化学方法——氢指数-苯酚/辛烷图解判识法。结果表明，沼泽环境覆水越深，煤中有机质富氢程度越高，生油气性能越好，裂解产物表现为正构烷烃和正构烯烃相对含量增加，以低本酚/辛烷值和高氢指数为特征；反之，沼泽环境覆水越浅，煤中有机质氢含量越低，裂解产物以高含量酚类化合物和芳香烃为特征，生油气性能关。由此表明，覆水型沼泽应是煤在烃，特别是煤成油生成的有利相带。     

Hydrocarbon genesis of Jurassic coal measures in the Turpan Basin, China

A typical case of coal-derived oils in China, i.e. the crude oils from the Middle-Lower Jurassic coal measure strata in the Turpan Basin, is presented. By means of oil-source correlation, it is confirmed that low maturity crude oil in the Shengjinkou oil field is derived from the coal-bearing Qiketai Formation of Middle Jurassic age, a brackish lacustrine sediment. Mature crude oils in the Qiketai oil field, and in well Taican 1, are sourced from the Badaowan Formation of Lower Jurassic age, which contains coal seams as thick as 100 m. Results show that commercial accumulations of liquid crude oils can be generated from coals and coal measure strata containing high volatile coal of bituminous rank. Despite unfavourable types of source material, the total hydrocarbon-generating potential can be great due to the unusual abundance of organic matter.     

典型盆地煤与油页岩共生成矿物质及古气候分析

选取煤与油页岩共生典型盆地山东黄县盆地、辽宁抚顺盆地、黑龙江依兰盆地和内蒙古金宝屯盆地,综合分析了其成矿物质特点,认为共生背景下煤岩中的低等动植物和油页岩中的高等植物均比单一矿种下含量高。这一规律可用于勘探、开发煤或油页岩单一矿种时预测其共生矿种存在的可能性。对古气候的分析表明,气候变换在一定程度上制约着煤与油页岩的共生模式,这种共生模式可为古气候研究提供一定依据,反之,通过古气候的变迁也可帮助勘探、开发共生背景下的煤与油页岩。     

鄂尔多斯盆地能源矿产氯仿沥青Sm-Nd同位素研究

对鄂尔多斯盆地石油、煤、含铀砂岩及其围岩的氯仿沥青进行了Sm-Nd同位素研究。结果表明,盆地流体(包括深部流体)活动具有多期性,且后期的流体活动对铀矿床的形成具有重要作用;赋存于同一套地层中的含铀砂岩沥青、煤沥青及石油沥青,虽然均具有富集地幔特征,但并非同期活动的产物;东胜矿区侏罗系直罗组煤沥青和盆地西南部陈家山矿区侏罗系延安组的煤沥青,源区时代上存在较大差异,伴生沥青并非全部由煤的热演化形成,可能还存在外来流体的加入,且东胜直罗组煤的伴生沥青较延安组煤的伴生沥青来源深度更大;盆地内马岭油田的直罗组石油沥青、陈家山延安组煤层石油沥青及其煤沥青在源区特征上具有内在联系。     

鄂尔多斯盆地中生界煤成烃潜力的实验研究

煤的热模拟实验研究表明:鄂尔多斯盆地侏罗系煤以产气为主,三叠系煤相对倾向于生油,三叠系煤的产油量是侏罗系煤产油量的 6~8倍,且产油温度宽,生成的气体成分以甲烷为主,但三叠系煤对液态沥青的吸附量大。侏罗系煤不仅产量小,产油持续的温度范围窄,而且生成大量的二氧化碳,但其排油效率高,对液态沥青的吸附量只有三叠系煤的 1/10。煤系有机显微组分组成和特征是造成中生界煤生烃潜力差异的主要原因。由于侏罗系煤生烃潜力低,且成熟度低,三叠系煤生油潜力虽高,但煤系规模小,煤层厚度薄,难以形成工业性油气藏。