Unconventional gas (including tight, shale, and coal seam gas) production has led to a drastic change of global energy landscape. The fundamental understanding of gas flow behaviours in unconventional gas reservoirs is essential to elevate the potential gas resource recovery. The behaviours of gas flow follow a chain of physicochemical processes in unconventional gas reservoirs, which can be labeled as “coupled processes” implying that one process affects the initiation and progress of another. This process chain is linked together through different disciplines, including geoscience, rock mechanics, multiphase flow, engineering chemistry, and thermodynamics, among others. Although progress on evaluation of migration, control, and recovery of unconventional gas has been achieved using mathematical models and physical experiments, the role of different fluids (e.g., CH4 and other hydrocarbons, CO2, and water) in unconventional gas flow is not well understood. Filling this knowledge gap is likely to play a critical impact on raising the potential of unconventional gas resource recovery and on reducing the environmental risks.

The overall theme of this special issue focuses on the impact of different fluids on flow behaviours and its impact on gas recovery. It serves as a platform for international researchers and practitioners from different disciplines to develop innovative solutions and to explore emerging technologies in key areas of shale and coal seam gas extraction.

This special issue presented contains 16 peer-reviewed papers to address technical and scientific aspects in unconventional gas reservoirs, topics covering physical behaviour of gas reservoir (4 articles), multiphase flow mechanics (5 articles), hydraulic fracturing mechanics (3 articles), and gas production (4 articles).

This special issue is organized as follows: (1)Part A: physical behaviour of gas reservoir(i)Triple-porosity modelling for the simulation of multiscale flow mechanisms in shale reservoirs(ii)Effects of maceral compositions of coal on methane adsorption heat(iii)Characteristics of pores under the influence of cyclic cryogenic liquid carbon dioxide using low-field nuclear magnetic resonance(iv)Real-time pore pressure detection—indicators and improved methods(2)Part B: multiphase flow mechanics(i)A numerical simulation study of the migration law of water-sand two-phase flow in broken rock mass(ii)A two-phase flowback model for multiscale diffusion and flow in fractured shale gas reservoirs(iii)Visualized experimental investigation on the gas-water distribution characteristics in intersecting fractures(iv)Study on pulse characteristic of produced crude composition in CO2 flooding pilot test(v)Investigating multiphase flow phenomena in fine-grained reservoir rocks: insights from using ethane permeability measurements over a range of pore pressures(3)Part C: hydraulic fracturing mechanics(i)Evolution of friction and permeability in a propped fracture under shear(ii)Back analysis of rock hydraulic fracturing by coupling numerical model and computational intelligent technology(iii)Brittleness evaluation of shale based on the Brazilian splitting test(4)Part D: issues related to gas production(i)Research on rapid identification and evaluation technology for gas formation while underbalanced drilling(ii)Methane extraction from abandoned mines by surface vertical wells: a case study in China(iii)Lateral percolation and its effect on shale gas accumulation on the basis of complex tectonic background(iv)Effects of formation dip on gas production from unconfined marine hydrate-bearing sediments through depressurization


This special issue was supported by the Fundamental Research Funds for the Central Universities (2017QNA06). We would like to thank all authors for their valuable contributions and all reviewers for their collaboration in providing rigorous peer-reviewed comments that greatly improved the accepted articles in this special issue.

Tongqiang Xia
Egor Dontsov
Zhongwei Chen
Fengshou Zhang
Mingyao Wei
Xiangzhao Kong