Reuse of Flowback and Produced Water: The Effects of Treatment Process on Tight-Rock Wettability and Selective Removal of Problematic ions for Stability of Friction Reducers
Creators: Zhang, Yanze
Publisher: name: University of Alberta Library
Year: 2022

<p>Oil and gas industry have faced significant operational, economic, and environmental challenges in recycling produced water. The treatment of produced water is highly researched, but few studies have evaluated the performance of treated produced water when used for hydraulic fracturing and enhanced oil recovery (EOR) operations. <br>
In this study, we treated various aqueous solutions, including synthetic formation brine (FB), sodium chloride (NaCl), calcium chloride (CaCl2), and sodium sulfate (Na2SO4), using an electro-oxidation (EO) process. The brine properties, including density, surface tension (ST), oil−water interfacial tension (IFT), viscosity, and pH, were compared before and after the treatment. Then, we conducted systematic contact-angle (CA) measurements and spontaneous imbibition tests using treated and untreated brine to study the effects of water treatment on rock−fluid interactions and its impact on oil recovery. The experimental results show that the effect of the EO process on ST, density, viscosity, and IFT was insignificant. However, the CA results show that the treated FB, NaCl, and Na2SO4 solutions exhibit stronger wetting characteristics compared with the untreated ones, while the treated CaCl2 solution exhibit weaker wetting characteristics compared with the untreated ones. We hypothesized that the change in the wetting characteristics was due to the generated oxidants from the EO process. We added OH−, H+, hydrogen peroxide (H2O2), and sodium hypochlorite (NaOCl) into untreated brine to test this hypothesis and monitored the CA variations. The results suggest that H2O2 and OH− can alter the wettability to more water-wet conditions in the NaCl solution but not in the CaCl2 solution. Furthermore, NaOCl results in wettability alteration to more oil-wet conditions in NaCl and CaCl2 solutions. The change in wettability to more water-wet conditions is mainly the result of the oxidation of dissolved organic matters, and the change to more oil-wet conditions is the result of the dissolution of high-valence cations, causing the cation bridging effect.<br>
We also studied the compatibility between produced formation brine and hydrolyzed polyacrylamide (HPAM). In our study, we conducted dynamic viscosity, particle size distribution, and viscoelasticity measurements to evaluate the performance of HPAM in DI water and formation brine (FB). The experimental results suggest that HPAM in FB has a much lower dynamic viscosity and shear stress profiles than in DI water. The storage modulus is higher than the loss modulus in the entire measured range when adding HPAM into FB, indicating a considerable curling of HPAM in the FB. We also conduct a sensitivity analysis to identify the problematic ions and their threshold concentration in the FB through dynamic viscosity measurement. Our results show that HPAM can only resist monovalent ions at low concentrations (&lt;1,000 ppm). The presence of divalent ions and iron ions at low concentrations (&lt;1,000 ppm, and &lt;100 ppm, respectively) may cause HPAM molecules to curl and significantly lose dynamic viscosity. The iron ions concentration at 1,000 ppm can cause HPAM molecules permanent damage.</p>