Waterless fluids in hydraulic fracturing - A review

Unconventional resources such as shale gas have attracted increasing global attention with great potential to bridge the energy supply chain. Yet the technical challenges and ecological concerns arise in the attempts to increase resource recovery. Shale reservoirs feature a low permeability water-sensitivity, and geological complexity, which call for more effective stimulation techniques to both reduce water use and boost production. It is believed that technology innovation such as waterless fracturing is the key to effectively improving unconventional resources recovery, while addressing the issue in reducing water consumption and environmental footprints. This paper investigates the development of two major waterless fracturing fluids, foams and liquid N-2/CO2, including the advantages and challenges faced with waterless fracturing, fracturing mechanisms, and fluid properties such as stability and rheology. Based on literature review, it is believed that foam has a great potential to be a promising fracturing fluid in improving productivity and long-term production with benefits such as fast cleanup, improved proppant transport, and minimal environmental footprint. Foam properties such as stability and rheology have been continuously improved with technological advances in the stabilizing agents. Foams stabilized by nanoparticles are reported to significantly improved foam stability and rheology under reservoir conditions over conventional surfactants. Other fracturing fluids such as liquid CO2/N-2 and gas fracturing fluids are designed to clear formation damage near the wellbore or for scenarios where long fractures are not desired, and both are faced with various technical challenges. This review provides readers with the state-of-the-art research progress regarding the technological advances of waterless fracturing fluids and sheds light on future research areas that can benefit a greener and more effective shale gas development.