Research advances in efficient exploration and development of coal measure gases and deep coallbed methane

SANG Shuxun; ZHENG Sijian; LIU Shiqi; ZHOU Xiaozhi; HAN Sijie; HUANG Fansheng; LIU Tong; DAI Xuguang

doi:10.13247/j.cnki.jcumt.20240375

Abstract：Coal measure gases and deep coalbed methane have become key areas for natural gas storage and production,as well as for the development of China's coalbed methane industry.Exploration and development are closely connected,and systematically summarizing the re-search progress of coal-measured methane in efficient exploration and development theories and technologies is of significant practical importance.Such summaries enhance understanding and offer valuable guidance for decision-making and engineering practices in the exploration and de-velopment of major basins and coal measures,including both coal-measured and deep coalbed methane.This article reviews the research achievements in coal measure gases and deep coal-bed methane exploration and development across three dimensions:the formation model and geological development of coal measure gases,the technology model and engineering develop-ment of coal-measured methane,and the key theoretical and technical aspects of efficient ex-ploration and development of deep coal seam gas.Furthermore,it addresses the author's view-points and potential breakthrough directions for six key issues:geological-engineering integra-tion,geological adaptability technology,co-production of coal measure gases/coalbed meth-ane,stress release coalbed methane development,the relationship between deep and interme-diate-shallow coal seam gas recoverability,and the development potential of stacked gas reser-voirs and gas-bearing systems across coal measures.The research has proposed basic coal measure gases reservoir formation models,such as thick-to-ultra-thick coalbed gas reservoirs,coal seam group gas reservoirs,coal measure gas reservoirs with overlapping coal-bearing sec-tions,tight gas reservoirs in non-coal-bearing sections of coal measures,deep coalbed methane reservoirs,and deep gas-bearing systems in the entire coal measures.Different reservoir for-mation models exhibit distinct geological characteristics for development.Based on the accu-mulation model and its reservoir geological characteristics,three basic coal measure gases de-velopment technology models have been proposed:single production,partitioned production,and co-production model.Each model is associated with specific technological approaches and distinct engineering characteristics.In the realm of deep coal seam gas geological theories,new insights have been gained into deep strata conditions,the occurrence of deep coal seam gas,the recoverability and reservoir transformability of coal seams,enrichment and high productivity laws,and sweet spot prediction and well deployment strategies.Breakthroughs have been a-chieved in deep coal seam gas development through innovations in large-scale volume fracturing technologies,such as"multi-stage fracturing with long-distance effective support"(the Yan-chuan South model)and"maximum volume fracturing in horizontal wells"(the Daning—Jix-ian model).But the geological,technological,and economic limits of fracturing scale are worth paying attention to.Rock mechanics and stratigraphic methods are the fundamental the-oretical bases for geological-engineering integration technology,particularly for integrated pre-diction technology targeting geology-engineering sweet spots.Rolling exploration,develop-ment,and production management technologies driven by geology-engineering feedback,are seen as critical breakthroughs in the field.Effective technologies for development must be a-daptable to both geological conditions and engineering control levels.Geological adaptability technologies encompass critical processes such as well type and wellbore structure,drilling and completion techniques,fracturing,and production control optimization.Further advancements are required in the integrated mechanisms and adaptation strategies within the technology sys-tem.Co-production of coal measure gases/coalbed methane represents a key technical break-through for large-scale and efficient development.Research into the technological feasibility of co-producing different types of unconventional gases in the coal measures and co-producing un-conventional gases and conventional natural gas through a single well-first partitioned produc-tion and later co-production,shows promise for significant engineering innovations.Substan-tial theoretical and technical progress has been made in stress-release coalbed gas development,achieving engineering feasibility.Coal seam gases that are difficult to develop,such as those controlled by structural features,have the potential to shift from development-constrained ar-eas to new zones with the increased storage and production capacity.This also provides critical technical support for the efficient development of deep coalbed methane in basins with low recoverability.Deep coal seam gas generally offers better recoverability than intermediate-shal-low coalbed methane,but its recoverability is still limited to basins with complex geological structures,such as the Ordos Basin,Junggar Basin,and Sichuan Basin.The implementation of stress relief technologies can facilitate the efficient extraction of deep coalbed methane,even in areas with low recoverability.However,realizing efficient development continues to faces numerous technical challenges.The formation mechanisms and integrated exploration and pro-duction technologies will remain focal points of ongoing research in the field of coal measure gases exploration and development.