Project Title: Micro-Crosslinked Plugging and Anti-Sloughing Drilling Fluid Technology for Deep Coalbed Methane Horizontal Wells and Its Large-Scale Application

Participating Enterprises: CCDC Drilling & Production Technology Research Institute
CCDC Changqing General Drilling Company

Award Received: Scientific and Technological Progress Award

Project Number: ECF-2026-SYE-1027

Main Participants: Wang Jingguang, He Huifeng, Zhang Xiaoping, Han Chengfu, Jia Jun, Meng Fanjin, Chen Lei, Liu Wei, Hou Bo, Liang Haijun, Sun Yaping, Hao Chao, He Wenting, Liang Hao, Sheng Tielin

Expert Review Comments:

Stable well construction is critical to developing deep coal reservoirs at scale. Guided by coal-rock collapse mechanisms, this project combines micro-crosslinked and micro/nanoscale sealing materials to stabilize formations with abundant bedding planes and fractures. The close connection between material design and wellbore-stability control is its principal strength. Applications in more than 150 wells in the Ordos Basin have supported safe lateral extension and reduced drilling complications. The related micro-crosslinked sealing and anti-collapse fluid technology is internationally leading. Its focused response to coal-rock instability and substantial field experience make it an important enabling technology for efficient development of comparable deep coalbed methane resources.

Main Innovations:

Revealed the instability mechanism of deep coal rock/coal gangue well walls, established a predictive model for deep coal rock well wall stability, proposed the 'multi-layer multi-level plugging for collapse prevention' method, developed deformable nanopolymer plugging agent G308 suitable for cross-link plugging on coal rock surfaces and the micro-nano fluid loss reducer G314 with both fluid loss reduction and plugging/collapse prevention functions, and built an efficient drilling fluid system for horizontal wells in deep coal seams of the Ordos Basin. Applied to over 150 wells in the Ordos Basin, it successively broke and created multiple domestic records, including the longest onshore coalbed methane horizontal section in China at 2500m and the deepest vertical coalbed methane horizontal well at 4113.95m, reducing downhole complexity by 75% and increasing the average horizontal section length by 32.6%.

Main Uses and Technical Principles:

Analysing the mechanism of wellbore collapse and instability during drilling of deep coal rock horizontal wells at depths greater than 2500 m, the core technology is 'multi-stage plugging with appropriate suppression'. By introducing non-polar long-chain oleophilic groups, the wettability of the micro-crosslinkable deformable nano-polymer plugging agent is modified from simple hydrophilicity to amphiphilicity, which helps form a dense plug layer on both the coal rock surface and the inner surface of the plug through adsorption, micro-crosslinking, and polymerisation, reducing permeability and improving collapse prevention. The system resists temperatures up to 150°C, has a mud cake toughness greater than 6.4 N, and the high-temperature high-pressure instantaneous filtration loss drops by 89.0%, basically solving the problems of coal seam collapse, coal gangue block drill jams, sand carrying in long horizontal sections, and lubrication and drag reduction difficulties in deep coalbed methane drilling in the Ordos Basin. The technology is overall at an internationally leading level.