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An effective evaluation on fracture network forming capacity is key to the whole process of shale gas exploration. At present, neither a clear standard nor a generally accepted evaluation method exist. In this study, a novel “Soundless Cracking Agent (SCA) fracturing evaluation method” was developed. The fractures were characterized quantitatively using fractal dimension of the trace on the core surface and areal density. Acoustic emission (AE) location was used for dynamic monitoring and analysis. The results show that the fractal dimension can be used for quantitative evaluation of complexity of fracture network. The higher the rock hardness, the smaller the fracture density after fracturing is; the higher the brittleness, the larger the fracture density after fracturing is. The development degree of natural fracture systems and sedimentary bedding is a key factor to control the propagating morphology of fractures. The number of AE events for sandstones with low clay content (<25%) is huge, and there are obvious take-off spots for cumulative curves and frequency distribution curves. The AE events for sandstones are distributed along the main fractures, with simple planar fractures clearly present after fracturing. But for shale, the number of AE events is less, with no obvious take-off spots, and AE events are scatteredly distributed. The higher the clay content and the lower the quartz content, the smaller the number of AE events is, and the smaller the frequency and the sound source amplitude are. For sandstone, the number of AE events decreased by about 75% due to the increase of clay content by 20%. The new method enables a comprehensive reflection of the characteristics of rock hardness, brittleness and natural fractures system. This work is valuable for the evaluation of hydraulic fracturing effects in unconventional oil and gas reservoirs in the future. [ABSTRACT FROM AUTHOR]

Highlights: [•] Hydraulic fracturing simulation experiments of shale outcrops were first carried out. [•] Fracture morphology was observed for the first time by high-energy CT scanning. [•] The effects of multiple factors on fractures propagating in shale play were studied. [•] CT scanning images were combined with internal fractures photographs for analysis. [•] Hydraulic fracturing of horizontal well was simulated for shale specimens. [Copyright &y& Elsevier]

• Water-gas relative permeability in hydrate-bearing porous media is studied by LBM. • Relationship between relative permeability and fluid distribution is characterized. • Effect of hydrate on water-gas relative permeability is revealed at a pore scale. The water-gas relative permeability is an important parameter to characterize multiphase flow in sediments. To study the water-gas relative permeability of hydrate-bearing porous media, multiphase flow simulations were carried out at the pore scale using the lattice Boltzmann method. The effects of hydrate saturation and hydrate-growth habits on the water-gas relative permeability, which is scaled by the relative permeability considering the hydrate only, were evaluated in a two-dimensional porous medium. Results show that the increase of hydrate saturation causes the decrease of water-gas effective permeability as expected. However, the effect of hydrate saturation on the water-gas relative permeability is different from that of hydrate saturation on the water-gas effective permeability. The water-gas relative permeability increases with the increase of hydrate saturation in the pore-filling case. The water-gas relative permeability decreases with the increase of hydrate saturation in the grain-coating case. The wettability of solid phase has a different effect on the relative permeability of wetting phase and nonwetting phase. The Jamin effect (phase blocking) was observed and may exist in the production of gas from natural gas hydrate reservoirs. This seriously affects the multiphase flow characteristics. The changes of microscale fluid distribution effect the changes of water-gas relative permeability. The relationship between the water-gas relative permeability and the characterization parameters of microscale fluid distribution was analyzed. [ABSTRACT FROM AUTHOR]