煤成气及鉴别理论研究进展

Coal-derived gas theory and its discrimination

煤系成烃理论形成经历了3个阶段:20世纪40年代发现煤能生气并可成藏,但未关注成油,创立了纯朴的煤成气理论;60年代发现煤中壳质组成油贡献大,可形成煤成油田,产生煤成油理论,但未关注成烃中的油气比例;70年代中国学者发现煤系成烃以气为主以油为辅,创立了完整的煤成气理论.煤系成烃以气为主以油为辅的根据:一是8个煤种中都发现有成气作用产物的气孔;二是煤的原始物质是由生气为主、低H/C原子值的纤维素和木质素组成;三是化学结构上煤以利于生气的甲基和缩合芳环为主;四是从泥炭至无烟煤热模拟实验获得大量气346~422 m3/t,只有少量轻质油.以往天然气类型鉴别以气相组分为主,现在把鉴别指标发展为气液固(干酪根)三相,扩大了鉴别范畴.从碳同位素、轻烃和生物标志物三方面,综合研制了鉴别煤成气和油型气的26个指标,还研编了若干鉴别图版和δ^(13)C-Ro关系式,提高了天然气鉴别可信度.煤成气理论开辟了天然气勘探新领域,使指导勘探天然气理论从"一元论"(油型气)发展为"两元论"(煤成气和油型气),为中国天然气工业快速发展提供了理论依据.2016年中国天然气和煤成气储量、产量与煤成气理论出现之前的1978年相比,分别提高了52,408,10和216.6倍,使中国从贫气国变为世界第6产气大国.

The formation of coal-derived gas theory experienced three stages.In 1940 s,a simple coal-derived gas theory was established.It was found that coal could generate gas and form reservoir,but no attraction was paid to oil generation from coal.In 1960 s,it was proposed the exinite in coal had great contribution to the generation of coal-derived oil.With large proportion of exinite,it could even form a coal-derived oil field.Thus the coal-derived oil theory came into being;however,no attention was paid to the oil/gas ratio during the hydrocarbon generation process.In 1970 s,the Chinese scholars found that hydrocarbon generation from coal measure was dominated by gas generation and supplemented by oil generation.Therefore,a complete coal-derived gas theory was established.The coal-derived gas theory was supported by the following evidences.（1） Pores indicative of gas generation products and traces were found in 8 kinds of coals;（2） cellulose and lignite with low H/C ratio account for 60%–80% among the original substances of woody plant in coal,which is dominated by gas generation;（3） humic kerogen is dominated by gas-prone methyl and condensed aromatic ring;（4） pyrolytic experiments on peat and anthracite get abundant gas products（346-422） m3/t,with a small amount of light oil.Therefore,a number of coal-derived gas fields were discovered in coal-bearing basins in the world.In the past,distinguishing of natural gas type is dominated by gas composition.In this study the distinguishing index was developed into three facies,i.e.,gas,liquid and solid（kerogen）,which broaden the distinguishing scope and index.Combined with carbon isotopes,light hydrocarbons and biomarkers,26 indexes were proposed to distinguish the coal-derived and oil-derived gases,and a series of plots and δ13 C-Ro relationships were compiled,which greatly improve the precision and reliability of gas distinguishing.The coal-derived gas theory opened a new natural gas exploration field,which leads to the change of guidance theory of natural gas exploration from monism（oil-derived gas） to dualism（coal-derived and oil-derived gases）,providing a theoretic basis for the rapid development of the Chinese natural gas industry.In 2016,the reserves of natural gas and coal-derived gas and production of natural gas and coal-derived gas increased by times of 52 and 408,10 and 216.6,respectively compared to that before the occurrence of coal-derived gas theory in 1978,which make China from a gas-poor country into the sixth major gas-producing country in the world.