Nanoparticle-Enhanced Hydraulic-Fracturing Fluids: A Review

Hydraulic-fracturing fluids are used to break down subterranean formations where oil and gas are trapped. Pad or prepad fluids are first pumped into the formation to generate the fracture geometry. Once the fracture geometry is created, additional fluid containing proppant is used to transport these solid particles into the fractures. Then, the hydraulic pressure is released and the fracture will tend to close. At that stage, the proppant prevents fracture closure and provides a conductive channel for hydrocarbons to flow into the wellbore. Biopolymers, synthetic polymers, foams, viscoelastic surfactant (VES) fluids, and slickwater are all used as fracturing fluids, each with properties that are beneficial under certain conditions. Today, their formulations are welldeveloped, and more recently, may incorporate smallsized particles in the nanometer size range. Such nanoparticles have addressed certain technological limitations of fracturing fluids. For example, VES fluids were reported to suffer high leakoff rates in moderate permeability reservoirs (200 md) and were limited in temperature (beyond approximately 220 degrees F, viscosity was diminished significantly). Another challenge is the pressuredependent behavior of boratecrosslinked gels, where the viscosity was found to drop significantly under high pressures. Also, in hightemperature reservoirs (>350 degrees F), it is very challenging to design a fluid that can sustain enough viscosity for a required period of time. Synthetic polymers (mainly acrylamidebased polymers) are commonly used and have been reported to be used at high concentrations. These highconcentration requirements are imposed by the need for a stable viscosity under hightemperature conditions. High polymer loading increases the potential of formation damage caused by the fluid residue. These challenges, which can be addressed by nanotechnology, could have a major impact on hydraulic- fracturing applications. For instance, the working temperature limit of VESbased fluids was improved from 200 to 250 degrees F (93 to 121 degrees C) by adding zinc oxide (ZnO) and magnesium oxide (MgO) nanoparticles. The boratecrosslinked gels were found to maintain their viscosity at pressures up to 20,000 psi when using boronic acidfunctionalized nanolatex silica particles as crosslinkers, while under such high pressures, conventional borate crosslinkers showed more than 80% reduction in viscosity. Moreover, the rheological properties of mixed VES/polymer fluids were enhanced when using nanoparticles. Use of foams can reduce the amount of water consumed in hydraulic fracturing. Alfa olefin sulfonate (AOS) surfactant can be foamed by use of carbon dioxide (CO2). Aluminum oxide nanoparticles were found to stabilize the foams created by AOS, VES, and CO2. This has a potential application in waterless fracturing. This review paper will capture all of these aspects and summarize the most recent experience of nanoparticle usage in hydraulic-fracturing fluids design.