**7.5 Alternative fracturing fluids**

Li et al. [116] conducted an experiment on the use of CO2 as pre-fracturing fluid during hydraulic fracturing in tight gas formations. They aimed to confirm that the combination of CO2 and water during hydraulic fracturing operations could help harness benefits of both fluids especially at locations with low water availability. This research was undertaken for subsequent application in the Loess plateau of Ordos basin in China. Results from experiments showed improved permeability due to dissolution of carbonates and clay minerals by CO2. They also found that CO2 interacts with hydrocarbons and provides additional impacts in terms of improving hydrocarbon properties to enhance relative permeability, thus providing increased productivity. More experiments should be conducted to ascertain the optimum use of CO2 and water combinations for fracturing.

Adverse environmental footprints of hydraulic fracturing operations have also necessitated research to find innovative ways of mitigating these impacts. Ellafi et al. [117] investigated the possibilities of re-using produced water as fracturing fluid. They justified their research by drawing attention to the large volumes of fresh water used in hydraulic fracturing operations. Some helpful statistics quoted to buttress their points include the following: Texans waste about 2% of water demand on fracturing jobs [118]; the amount of water withdrawn from the Missouri River for hydraulic fracturing in 2018 alone, was about 1.269x 1010 gals, an estimated 10.1% of North Dakota water consumption [119].
