Theoretical and technological difficulties and countermeasures of deep CBM exploration and development in the eastern edge of Ordos Basin

Deep coalbed methane (CBM) resources (hereinafter referred to the CBM resources with the buried depth greater than 2 000 m) are abundant in China and have great potential in exploration and development. Since 2019, Daning‒Jixian block in the eastern edge of Ordos Basin has entered the stage of "scaled exploration + pilot test" of deep CBM, with the daily gas production exceeding 2 × 10⁴ m³ in vertical wells and 10 × 10⁴ m³ in horizontal wells. This remarkable achievement has broken through the traditional depth limitation in CBM exploration and development. Thus, the total resource of CBM is expected to increase significantly on the basis of 30.05 × 10¹² m³, and the deep CBM resource will become a key direction of exploration and development for the scaled development of CBM industry in the "fourteenth five year plan" and even in long term. In view of the urgent needs of development mode with traditional surface drilling, fracturing (reservoir stimulation), drainage and production (lifting), gathering and digital intelligence as the main technologies, many basic theoretical and technical difficulties are faced in the development of the deep CBM in the eastern edge of Ordos Basin: the optimization method of favorable areas based on accumulation mechanism and occurrence state, the main control factors and control mechanism of high yield, the desorption-seepage mechanism and development law, the evaluation standard of development dessert with “geology-engineering integration”, and the determination method and basis of key development indicators, the low-cost, fast and efficient drilling and completion technology, the efficient cement sheath sealing control technology for horizontal wells, the formation mechanism of deep coal rock fracture network, the low-cost, efficient and environmentally friendly fracturing materials, the porous and permeable characteristics and flow law of fracture network after fracturing, the drainage and lifting control technology under the working conditions of high salinity, high water-gas ratio and sand production, the theory and practice system for stable operation of complex gathering pipeline network required for the efficient and energy-saving gathering and the scaled development, the digital and intelligent construction of gas field, and the application research of artificial intelligence. On the basis of systematically sorting out the above difficulties, the research direction and specific countermeasures were put forward for the theory and technology on exploration geology, development geology, well drilling and completion, fracturing (reservoir stimulation), drainage production (lifting), gathering and digital intelligence. This achievement not only has important guiding significance for accelerating the scaled production of deep CBM in the eastern edge of Ordos Basin, but also has a strong leading and demonstration role for the scaled development of deep CBM at home and abroad. In addition, it could also effectively promote the high-quality development of CBM industry, and support the realization of the national goal of "carbon peaking and carbon neutrality", so as to ensure the security of clean energy.