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

Breakthroughs in the exploration and production of deep coalbed methane (CBM) in the Daning-Jixian block on the eastern margin of the Ordos Basin exert a profound influence on the CBM industry, arousing extensive concern and follow-up. Although previous studies delved into the theoretical and technical challenges and corresponding solutions of deep CBM exploration and production, there is a lack a systematic summary of pilot tests for typical gas field exploitation. Through an in-depth dissection of the geological characteristics and challenges of cost-effective production of deep CBM, this study summarized the advances and outcomes of the pilot test projects in the Daning-Jixian block, determined the production patterns, and proposed strategies for cost-effective production. The results show that: (1) Deep coal seams exhibit extensive distributions, high gas content, rich free gas, favorable preservation conditions and coal structures, high brittleness index, and high 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 result in significantly distinct production characteristics of gas wells. Therefore, by determining the production capacity of gas wells and the adaptive production technologies through pilot tests, the production risks caused by the high heterogeneity of coal seams can be effectively reduced using the progressive production mode. (3) Artificial gas reservoirs with highly bridged well patterns and fracturing networks, constructed based on the optimized geo-engineering integrated well pattern design, 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 owing to their production characteristics such as early gas production, rapid production addition, high initial gas production, and rapid decline. Nevertheless, long-term stable production of gas fields requires continuous drilling of new wells. (6) Given 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, manifesting high quality and a production possibility, meet the requirements of rapid technological promotion and duplication. The deep CBM production in the Daning-Jixian block can provide a technical reference for the large-scale production of deep CBM in China's other blocks, holding great significance for accelerating the exploration and production of deep CBM in the country.