煤系气聚集系统与开发地质研究战略思考

Strategic thinking on research of coal measure gas accumulation system and development geology

我国煤系天然气(简称“煤系气”)“增储上产”空间巨大,国家能源安全战略价值显著,然而目前资源探明率及动用率极低,反差极大。鉴于此,分析了煤系气地质内涵和基本特点,论述了近年来生产实践揭示的重大研究需求,思考了新一轮地质科技攻关战略方向,提出了亟待突破的关键科学技术问题。我国煤系气成藏与开发地质研究近期核心进展体现在3个方面:揭示了煤系气六大基本地质特点,发现了煤系气成藏作用“深度效应”,初步建立了煤系气勘查-开发工程一体化地质技术系列。同时,近年来勘探开发实践展示出正反2方面典型实例:煤系气合采井产气量并非随产(储)层组的层数增多、累计厚度增大而增高,“1+n”<n乃至<1的产气效果较为普遍;某些深部煤层气井长期稳定在较高产气水平,颠覆了深部煤储层产能低、产气量衰减快的传统认知;薄互层煤系具有更高的产气潜力,而我国业界长期对此关注甚少。分析认为,我国煤系气目前开发效果不理想的地质原因在于4个方面:①煤系气地质条件特殊性认识尚待深化;②业界多年来陷入煤系气的非常规属性思维定势,忽略了其常规地质属性,导致新领域新层系探索力度不足;③可形成超大型聚集及大规模生产的薄互层煤系气总体上属于常规天然气,开发潜力巨大;④对非常规煤系气地质属性了解相对较多,但对常规煤系气地质条件特殊性仍知之甚少。建议围绕“煤系天然气共生聚集系统与有序开发地质原理”这一主题开展研究:①揭示深煤层天然气赋存态与解吸机制,形成深部煤层气优质储层预测理论与技术体系;②阐明煤系气聚集过程与成藏效应,形成煤系气开发地质条件预测理论体系,完善煤系气甜点区段优选方法;③研究薄互层煤系气成藏特点与优质开发层段地质控制,建立薄互层煤系气聚集与配分理论体系,发展薄互层煤系气甜点区段预测方法;④探索煤系气有序开发地质原理与技术基础,形成煤系气高效有序合采技术基础。

Coal measures natural gas(CMG)resource in China has a huge space to“increase reserve and production”and significantly strategic value for national energy security.However,the proved ratio and utilization ratio of the resource are very low,which is in great contrast to abundant CMG resources.Therefore,in this study,the geological connotation and basic characteristics of CMG are analyzed,the major research needs revealed by production practice in recent years are discussed,the strategic direction for a new round of tackling key problems in geological science and technology is considered,and the key scientific and technological problems that need to be solved urgently are put forward.In recent years,the key progress of the research on the geology of CMG accumulation and development in China is reflected in three aspects:revealing six basic geological characteristics of CMG,discovering the“depth effect”of CMG accumulation,and initially establishing the geological technology series of CMG exploration and development engineering integration.At the same time,the exploration and development practice in recent years shows some typical examples:the gas production of CMG co-production wells does not increase with the increase of the number and the cumulative thickness of production(reservoir)layers,and the gas production effect of“1+n”less than“n”or even less than 1 is more common;some deep coalbed methane(CBM)wells are stable at a higher gas production level for a long time,which overturns the traditional cognition of low gas production capacity and rapid production decline of deep coal reservoir;and the thin interbedded coal measures have higher gas production potential,but the industry in China has paid little attention to it for a long time.The geological reasons for the unsatisfactory effect of CMG development in China lie in four aspects:firstly,the understanding of the particularity of CMG geological conditions remains to be deepened;secondly,the industry has been trapped in the thinking pattern of unconventional attributes of CMG for many years,ignoring its conventional geological attributes,resulting in poor exploration of new fields and new strata;thirdly,the thin interbedded CMG,which can form super large-scale gas accumulation and production,generally belongs to conventional natural gas;fourthly,the geological properties of unconventional CMG are known more,but the particularity of the geological conditions of conventional CMG little.It is suggested that the future research should be carried out around the theme“CMG symbiotic accumulation system and orderly development geological principle”:firstly,revealing the occurrence state and desorption mechanism of deep CBM,and forming the prediction theory and technology system of deep high-quality CBM reservoir;secondly,clarifying the accumulation process and effect of CMG,forming the prediction theory system of geological conditions for CMG development,and improving the optimization method of favorable CMG target area and stratigraphic section;thirdly,studying the characteristics of thin interbedded CMG accumulation and geological control of high-quality production intervals,establishing the theoretical system of thin interbedded CMG accumulation and distribution,and developing the prediction method of favorable CMG target area in thin interbedded coal measures;fourthly,exploring the geological principle and technical basis of orderly CMG development,and forming the technical basis of efficient and orderly CMG co-production.