The Impact of Salt Ions on the Rheology of a Crosslinked Polymer Containing a Chelating Agent

Abstract

AbstractThe growth in hydraulic fracturing activities increased the demand for freshwater, a scarce commodity in water-deprived regions. The alternative is to utilize seawater (SW) or produced water (PW) from oil and gas operations to formulate high total dissolved solids (TDS) fracturing fluids. If achieved, it will result in more sustainable hydraulic fracturing operations that are cost and logistics efficient. Furthermore, aside from the hydrocarbons in PW, both SW and PW have similar ions, so the same remedy should be suitable for both. Therefore, this study investigates the influence of individual ions on a crosslinked polymer solution that contains a chelating agent.The study investigated the effect of individual ions on the rheology of fracturing fluid formulated using carboxy methyl hydroxy propyl guar (CMHPG) polymer. The studied salts included calcium chloride (CaCl2.2H2O), magnesium chloride (MgCl2.6H2O), sodium chloride (NaCl), and sodium sulfate (Na2SO4). First, the effect of delayed zirconium (Zr) crosslinker on individual ions was investigated by varying the Zr concentrations (0.3, 0.6, and 1 wt. %). Then, the selected crosslinker concentration was used to inspect the impact of N, N-Dicarboxymethyl glutamic acid (GLDA) chelating agent on the crosslinked system at different concentrations (4, 10, and 20 wt. %). Finally, the rheology of polymer in SW and deionized water (DW) was tested as a reference. The testing parameters on the two sets of the experiments were constant, which included 70 °C temperature, 500 psi pressure, 100 1/s shear rate, and 45 minutes for polymer hydration in a fluid.The rheology of the crosslinked CMHPG polymer was mostly impacted by sulfate and then calcium ions. The viscosity of the solution containing only sodium sulfate was reduced to that of SW. Unlike the DW, the increase in the crosslinker concentration increased the viscosity of SW and individual ion solutions. The ions’ salinity affected the long-term viscosities as they dropped to less than 10 cP in all concentrations in less than one hour. Sodium and magnesium ions did not significantly impact the solution viscosity and behaved like that of DW. The low-concentration chelating agent raised the stability of MgCl and DI solutions. In the SW, NaCl, and CaCl2, the viscosity dropped at the first 20 minutes then the curve rose to reach higher values than the DI after 3 hours.This work demonstrated how the crosslinker and chelating agent affect different salt systems’ behavior and viscosity. The results can be used to understand the rheology of fracturing fluids based on seawater or produced water.