Outcomes and implications of pilot tests for deep coalbed methane production on the eastern margin of the Ordos Basin

The Breakthroughs in the exploration and production of deep coalbed methane (CBM) in the Daning-Jixian block on the eastern margin of the Ordos Basin have had a profound influence on the CBM industry, attracting extensive attention and follow-up. Although previous studies have delved into the theoretical and technical challenges and corresponding solutions for deep CBM exploration and production, there is a lack of a systematic summary of pilot tests for typical gas field exploitation. By conducting an in-depth analysis of the geological characteristics and challenges of cost-effective production of deep CBM, this study summarizes the advances and outcomes of the pilot test projects in the Daning-Jixian block, identifies production patterns, and proposes strategies for cost-effective production. The results show that: (1) Deep coal seams have extensive distributions, high gas content, rich free gas, favorable preservation conditions, good coal structures, high brittleness index, and strong sealing capacities of coal seam roof and floor. However, factors such as the presence of microstructures, extremely low permeability, and high total dissolved solids (TDS) content restrict the cost-effective production of deep CBM. (2) Different geological conditions lead to significantly distinct production characteristics of gas wells. By determining the production capacity of gas wells and identifying adaptive production technologies through pilot tests, the production risks associated with the high heterogeneity of coal seams can be effectively reduced using a progressive production mode. (3) Artificial gas reservoirs with highly bridged well patterns and fracturing networks, constructed using optimized geo-engineering integrated well pattern designs, can maximize resource production and recovery. (4) The large-scale, high-injection-rate limit volume fracturing technology, characterized by long horizontal sections, multiple sections and clusters, and large proppant volumes, can increase effective stimulated reservoir volumes and well-controlled reserves, thus substantially enhancing single-well production. (5) Deep CBM wells can achieve short-term rapid large-scale production growth due to their characteristics such as early gas production, rapid production increase, high initial gas production, and rapid decline. However, long-term stable production of gas fields requires continuous drilling of new wells. (6) Given the high early-stage production costs, it is necessary to constantly improve the engineering operation efficiency and reduce production costs in order to achieve cost-effective production. Overall, deep CBM resources, demonstrating high quality and production potential, meet the requirements for rapid technological promotion and replication. The deep CBM production in the Daning-Jixian block can provide a technical reference for the large-scale production of deep CBM in other blocks in China, holding great significance for accelerating the exploration and production of deep CBM in the country.