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

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.