Geological characteristics and co-exploration and co-production methods of Upper Permian Longtan coal measure gas in Yangmeishu Syncline, Western Guizhou Province, China

Coal measure gas(also known as coal-bearing unconventional gas)is the key field and development direction of unconventional natural gas in recent years.The exploration and evaluation of coal measure gas(coalbed methane,coal shale gas and coal measure tight sandstone gas)from single coalbed methane has greatly expanded the field and space of resource evaluation,which is of positive significance for realizing the comprehensive utilization of coal resources,maximizing the benefits and promoting the innovation of oil and gas geological theory and technological advances in exploration and development.For the first time,in Yangmeishu Syncline of Western Guizhou Province,the public welfare coalbed methane geological survey project of China Geological Survey has been carried out a systematic geological survey of coal measure gas for the Upper Permian Longtan Formation,identified the geological conditions of coal measure gas and found high quality resources.The total geological resource quantity of coalbed methane and coal shale gas is 51.423×109 m3 and the geological resource abundance is up to 566×106 m3/km2.In this area,the coal measures are characterized by many layers of minable coal seams,large total thickness,thin to the medium thickness of the single layer,good gas-bearing property of coal seams and coal measure mudstone and sandstone,good reservoir physical property and high-pressure coefficient.According to the principle of combination of high quality and similarity of key parameters of the coal reservoir,the most favorable intervals are No.5-2,No.7 and No.13-2 coal seam in Well YMC1.And the pilot tests are carried out on coal seams and roof silty mudstone,such as staged perforation,increasing hydraulic fracturing scale and"three gas"production.The high and stable industrial gas flow with a daily gas output of more than 4000 m3 has been obtained,which has realized the breakthrough in the geological survey of coal measure gas in Southwest China.Based on the above investigation results,the geological characteristics of coal measure gas in the multi-thin-coal-seam-developed area and the coexploration and co-production methods,such as the optimization method of favorable intervals,the highefficiency fracturing and reservoir reconstruction method of coal measures,and the"three gas"drainage and production system,are systematically summarized in this paper.It will provide a reference for efficient exploration and development of coal measure gas in similar geological conditions in China.

Coal measure metallogeny:Metallogenic system and implication for resource and environment

Coal,coal measure gas,coal conversion to oil and gas,and coal-based new materials are reliable guarantees for stable energy supply and economic and social development in China.The coal-dominated resource endowment and the economic and social development stage determine the irreplaceable position of coal resources in the energy system.Coal measure resources,including aggregated or dispersed solids,liquid and gaseous multitype energies,and metal as well as nonmetallic minerals,are the products of multisphere interaction and metallogenetic materials generation,migration,and accumulation.Coal measures record rich deep-time geological information of transitional and terrestrial peat bogs,which is a crucial carrier to reveal ecosystem evolution,significant organic carbon sequestration,atmospheric O_(2)/CO_(2)variation,and wildfire events.Coal measure evolution is accompanied by the migration and transformation of various materials during diagenesis-metamorphism,forming differentiated coal compositions besides properties and various mineral resources in its adjacent strata.The enrichment condition,occurrence state,and separation potential are the premise for level-by-level use and efficient development of coal measure resources.Coal measure metallogeny is based on the metallogenic system of multiple energy and mineral resources in coal measures and their environmental effects.Fully understanding coal measure metallogeny is beneficial for promoting the coal transition from fuel to raw materials and strengthening its attribute of multiple mineral resources.The metallogeny comprises various aspects,including:(1)the symbiosis mechanism,co-exploration and co-mining conditions of various resources;(2)the source-sink system of ore-forming materials;(3)the differential carbon accumulation and hydrogen enrichment effect;(4)organic(coal and hydrocarbon)and inorganic(mineral)interactions;and(5)combination of minerals naturally enrichment during the metallogenic process and artificial enrichment during the ore processing process.The coal measure metallogeny belongs to the geoscience disciplines,and studies the types,formation,distribution,enrichment mechanisms,evaluation methods,and development strategies of resources related to coal measures.The key scientific problems include geological records related to mineral enrichment processes,metallogenic mechanisms,resource distribution,occurrence evaluation,and accurate development.Developing coal measure metallogeny is significant in improving the critical mineral metallogenic theory,revealing various deep-time earth systems and realizing the national energy transformation and high-quality development.