Unconventional reservoirs generally cannot be commercially developed without hydraulic fracturing or other engineering methods. Over recent decades, a series of stimulation techniques have been developed to enhance tight gas reservoirs, including hydraulic fracturing, hydraulic slotting, and hydraulic punching, in addition to some waterless stimulation techniques like CO2-enhanced coalbed methane recovery (CO2-ECBM) and N2-ECBM. Some potential stimulation methods have also been proposed in the laboratory and trials are being conducted in the field, such as cryogenic liquid nitrogen, microwave heating, and high-voltage electrical stimulation techniques. More importantly, new methods and technologies are emerging for the optimisation of unconventional natural gas production, from both geology and engineering perspectives.

Coalbed and shale gas reservoirs are characterised by greater heterogeneity, multiple gas storage mechanisms, and unique attributes that control production performance. Hundreds of thousands of coalbed methane and shale gas wells are in decline or are producing minimal volumes, including many older-generation shale wells. Various methods have been adopted to improve gas recovery, including, but not limited to, high-precision characterisation of coal and shale reservoirs at multi-scales, fast drilling and completion of wells with long laterals as well as large-scale volume fracturing, and new technologies such as multiple well-type development, fluid injection, nano-flooding and enhancing biogenic methane generation methods. Apart from these, attention is continuously being directed towards the better selection of “sweet” areas and “sweet” sections for better gas production performance. Recently, with the application of big data and artificial intelligence, new theories and technologies are emerging to improve gas production. Careful selection of technologies is essential for long-term success, confident decisions, and increased operational efficiency in unconventional plays.

The aim of this Special Issue is to report on the state of the art in fundamental and practical aspects of new technologies and to summarise the results of enhancing methane production research and field tests. We hope to focus both on progress in new methods as well as new technique development. We welcome both original research and review articles.

Potential topics include but are not limited to the following:

• Recovery mechanisms of natural gas from heterogeneous reservoirs
• Identifying and mapping of sweet sections and spots
• Multiphase flow and water-rock interactions in coal and shale
• Methods for improving low efficiency well performance
• Advanced numerical and analytical modelling in predicting production performance
• Enhanced unconventional gas production using CO2, N2, and other mixed gases
• Biogenic methods for enhancing coalbed methane and shale gas production
• Enhancing completion and stimulation strategies
• Formation damage in coalbed methane and shale gas recovery
• Other geological and engineering issues associated with enhancing coalbed methane and shale gas production