Liquid nitrogen waterless fracking for the environmental protection of arid areas during unconventional resource extraction

Many arid and semi-arid regions are rich in shale gas or coalbed methane. However, hydraulic-fracturing, commonly used for reservoir stimulation, has serious environmental impacts such as the consumption of large quantities of water, damage of residual organic compounds and the disposal of process water. This paper presents liquid nitrogen (LN2) as an environmentally friendly, waterless fracking technology, which could potentially replace hydraulic fracturing. Laboratory experiments on LN2 fracturing were conducted on coal samples, and high-resolution micro X-ray computed tomography was used for 3D visualization and evaluation of fracture evolution characteristics, including liquid nitrogen cyclic quenching, effect of initial fracture size (IFS) and coal saturation. The findings of this study testify to the effectiveness of fracturing by LN2 quenching on coalbed methane reservoirs. This technique would help protect water resources and alleviate other environmental concerns in arid districts during unconventional resource recovery. (C) 2020 Elsevier B.V. All rights reserved.