*4.1.3 Gas fracturing fluid*

Gas fracturing involves the injection of gas at high pressures into the subsurface in order to create fractures within targeted reservoir locations. Nitrogen gas is the most employed gas for fracturing purposes, due to its obvious advantages of availability, its inert nature and of course, cost [59]. The main limitation of gas fracturing is the depth it can be used as a fracturing fluid since it has a low density and thus is restricted to reservoirs of less than 5000 feet deep [60]. Recent advancements in ultra-light weight proppants [50, 61] provides positive prospects that may counter the depth limitation of gas fracturing to some extent.
