Deep coalbed methane production technology for the eastern margin of the Ordos Basin: Advances and their implications

Contrasting with shallow to moderately deep coalbed methane (CBM) reservoirs, deep CBM reservoirs exhibit favorable coal structures, high formation pressure, high free gas ratios, and high contents of total dissolved solids (TDS) and CO₂. Extensive fracturing allows for CBM flowing at the initial stage, while the production parameters vary significantly throughout the CBM production. This requires wide technological boundaries of the main production technologies. Compared to shale gas and tight gas, deep CBM manifests different production mechanisms and relatively low free gas ratios, which lead to short flowing cycles of CBM. This necessitates timely water withdrawal for CBM production. Moreover, deep CBM wells remain in a low-production stage dominated by desorption for a long time. Based on the geological characteristics of deep coal reservoirs, this study investigated the Daning-Jixian block on the eastern margin of the Ordos Basin. It systematically analyzed the factors influencing deep CBM production, like stress sensitivity effect, velocity sensitivity, scaling blockage, Jamin effect, and free gas ratio, as well as their characteristics. Accordingly, this study pinpointed some technological challenges in deep CBM production: unknown conversion time limit between free and desorption gases, prominent corrosion and scaling caused by CO₂ and water with high TDS content, and short pump inspection cycles of horizontal wells. To minimize the bottomhole pressure, boost CBM desorption, and enhance the single-well estimated ultimate recovery (EUR), this study proposed the hydraulic jet pump lifting technology, which is the most suitable for horizontal well production currently and yields the optimal economic efficiency. Moreover, this study pointed out the research directions of production and hydraulic jet pump lifting technologies for deep CBM to transition into green and intelligent gas field development, including strengthening integrated geological-engineering research, establishing efficient CBM production systems, and exploring and testing integrated rodless lifting production technology.