(159q) Ph-Responsive Viscoelastic Gel Based on Dynamic Binary Complex As Viscosity Modifying Agent for Hydraulic Fracturing

Petroleum and natural gas accounted for about seventy percent of the primary energy consumption in the United States. Production of natural gas and crude oil through the extraction technologies horizontal drilling and hydraulic fracturing from the unconventional reservoir has increased to more than half among the natural gas and crude oil production in the past decades of the United States. Hydraulic fracturing is a key technique of extracting oil and gas to improve the recovery rate in the unconventional reservoir. However, according to recent research, the unconventional reservoir's oil and gas recovery is estimated lower than twenty percent. The fracturing process injects several million gallons of fluid with proppant at high pressure to create fissures and cracks in the shale. One of the important factors that impact the fracturing is the viscosity modifying agent of the fracturing fluid which provide driven force to transfer the proppant into cracks. Herein, we describe a novel viscosity modifying agent of hydraulic fracturing fluid developed by a dynamic binary complex (DBC) with pH-responsive viscosity. The novel DBC is relying on the complexation of a long chain zwitterionic type surfactant involving carboxyl acid head with diethylenetriamine in the water. At a concentration of 2 wt% of DBC, the fluid displaced zero-viscosities from 9,000 to 200,000 cP, corresponding to a reversible pH adjusting. Moreover, the viscosity behavior of DBC was studied as a function of temperature and salinity to evaluate the potential application in the unconventional reservoir. At a two wt% concentration and optimized pH, the DBC displayed 1.4 orders of magnitude lower sand settling velocity compare to 2 wt% of polyacrylamide solutions at room temperature. Meanwhile, a 1.0 order of magnitude lower sand settling velocity of DBC was observed compared to the polyacrylamide solutions at 195°F. Unlike polymers whose structure would be broken down at high temperatures, the DBC system displayed better thermal stability. By adjusting the pH from 4 to 8, the network structure of the gel could be deformed that has lack of macromolecular residues could be beneficial for the fracturing process. Besides, the reusability and no need for gel breakers are suitable for the economy and environment.