A Critical Review of Hydraulic Fracturing Fluids over the Last Decade

Abstract

AbstractHydraulic fracturing is a well-established process to enhance productivity of oil and gas wells. Fluids are used in fracture initiation and the subsequent proppant and/or sand transport. Several chemistries exist for these fluids. This paper summarizes the published literature over the last decade (90+ technical articles) and captures the advances in the design of water-based fracturing fluids. Despite their old introduction, guar-based polymers are still being used in fracturing operations for wells at temperatures less than 300°F (148.9°C). In order to minimize the damage associated with this class of polymers, the industry attempted several approaches. These include the use of lower polymer concentration in formulating these fluids. Another approach was to alter the crosslinker chemistry so that one can generate higher viscosity values with lower polymer loadings. Moreover, the industry shifted towards the use of cleaner guar-based polymers. The reason is the fact that commercial guar contains a minimum of 5 wt.% residues that cause damage to proppant packs. With fracturing deeper wells in hotter reservoirs, the need arose for a new class of thermally stable polymers. Thus, the industry shifted towards polyacrylamide-based polymers. These synthetic polymers offer sufficient viscosity at temperatures up to 232°C (450°F). Examples included 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and copolymers of partially hydrolyzed polyacrylamide (PHPA)-AMPS-vinyl phosphonate (PAV). To address the challenge of high pressure pumping requirements on the surface, high density brines have been used to increase the hydrostatic pressure by 30%. On the breakers chemistry, new breakers were introduced. These breakers decrosslink the gel by reacting with the crosslinker. In order to minimize the environmental impact of using massive amounts of fresh water and to minimize costs associated with treating produced water, the use of produced water in hydraulic fracturing treatments has been reported. In addition, the paper captures the advancements in the use of slickwater where use is made of drag reducing agents (PAM-based polymers) to minimize friction. The paper highlights the first use of breakers that were introduced to improve the cleanup of these drag reducers. For foamed fluids, new viscoelastic surfactants (VES) that are compatible with CO2 are discussed. The paper also sheds light on the use of emerging technologies such as nanotechnology in the design of new efficient hydraulic fracturing fluids. For example, nanolatex silica was used to reduce the concentration of boron used in conventional crosslinkers. Another advancement in nanotechnology was the use of 20 nm silica particles suspended in guar gels. The paper provides a thorough review on all of these advancements.