Project Title: Optimization of Post-Frac Flowback Control in Deep Coalbed Methane

Participating Enterprises: CNPC Chuanqing Drilling Engineering Co., Ltd., Changqing Downhole Technology Company

Award Received: Scientific and Technological Progress Award

Project Number: ECF-2026-SYE-1006

Main Participants: Wang Kongjie, Xu Hongxing, Chen Fei, Li Zefeng, Li Shanshan, Zhang Kang, Ji Suibo, Wang Yaru, Zhang Fazhong

Expert Review Comments:

The strength of this project is its explicit balance between effective fluid recovery and preservation of fracture conductivity. Flowback is optimized against two operational risks: proppant return and coal-fines blockage. Laboratory investigation of fines transport and a pressure-coupled fracture–wellbore–wellhead model translate the effects of flow rate, gas–water ratio and fracture conditions into well-specific operating charts. Application in 39 wells demonstrates the method’s practicality. The achievement gives field teams a stronger basis for adjusting flowback schedules, reducing reliance on experience alone and protecting the conductive pathways created by fracturing. It is a useful tool for post-fracturing management of comparable deep coalbed methane wells.

Main Innovations:

This study has ascertained the material sources of coal fines that invade hydraulic fractures in deep coalbed methane (CBM) reservoirs, elucidated the retention and blockage mechanisms of coal fines within fractures, and characterized the associated impairment of fracture conductivity. The influences of flow velocity, gas-water ratio, fracture width, and confining pressure on coal fines retention and blockage were systematically investigated. Subsequently, a comprehensive flowback model coupling the fracture, wellbore, and wellhead was established through pressure coupling. An optimization strategy for flowback scheduling was proposed, with the dual objectives of preventing proppant backflow and 4 mitigating fine-induced blockage within fractures. Finally, a practical and user-friendly customized flowback chart was developed for deep CBM wells, tailored specifically to individual well conditions.

Main Uses and Technical Principles:

This technique establishes flowback optimization objectives for deep coalbed methane (CBM) under multi-factor control, built upon laboratory experiments and a thorough characterization of coal-fine sources and retention behavior within fractures. A pressure-coupled full-path flowback mathematical model—spanning the fracture, wellbore, and wellhead—is developed by integrating choke models, wellbore gas-liquid flow models, fracture fluid seepage models, and micromechanical analyses of proppant and coal fines. This is accompanied by a customized flowback chart tailored to individual wells. The technique provides a scientific basis for post-fracturing flowback, ensuring rapid, stable, and efficient cleanup and production, while mitigating engineering risks such as sand production and fracture conductivity loss. It overcomes the long-standing reliance on empirical scheduling that lacks theoretical support, thereby filling a critical technological gap.