Rheological Study of Seawater-Based Fracturing Fluid Containing Polymer, Crosslinker, and Chelating Agent

Abstract

Freshwater is usually used in hydraulic fracturing as it is less damaging to the formation and is compatible with the chemical additives. In recent years, seawater has been the subject of extensive research to reduce freshwater consumption. The study aims to optimize the rheology of seawater-based fracturing fluid with chemical additives that reduce the formation damage. The studied formulation consists of a polymer, a crosslinker, and a chelating agent to reduce seawater hardness. We used a standard industry rheometer to perform the rheology tests. By comparing five distinct grades [hydroxypropyl guar (HPG) and carboxymethyl hydroxypropyl guar (CMHPG)], we selected the guar derivative with the best rheological performance in seawater. Five different polymers (0.6 wt %) were hydrated with seawater and freshwater to select the suitable one. Then, the best performing polymer was chosen to be tested with (1.6, 4, and 8 wt %) N , N -dicarboxymethyl glutamic acid GLDA chelating agent and 1 wt % zirconium crosslinker. In the first part, the testing parameters were 120 °C temperature, 500 psi pressure, and 100 1/s shear rate. Then, the same formulations were tested at a ramped temperature between 25 and 120 °C. We observed that higher and more stable viscosity levels can be achieved by adding the GLDA after polymer hydration. In seawater, an instantaneous crosslinking occurs once the crosslinker is added even at room temperature, while in freshwater, the crosslinker is activated by ramping the temperature. We noted that, in the presence of a crosslinker, small changes in the chelating agent concentration have a considerable impact on the fluid rheology, as demonstrated in ramped temperature results. It is observed that the viscosities are higher and more persistent at lower concentrations of GLDA than at higher concentrations. The study shows the rheological response when different chemical additives are mixed in saline water for hydraulic fracturing applications.

Effect of Seawater Ions on Polymer Hydration in the Presence of a Chelating Agent: Application to Hydraulic Fracturing

“…SW and Na 2 SO 4 were not stable and had much lower viscosity compared to the other solutions. Similar results of DI and SW were achieved in a similar study . From the figure, it can be concluded that Na 2 SO 4 is the source of viscosity reduction of the SW.…”

“… Dissolvine StimWell DGH GLDA structure—GLDA-Na 4 . 22 Reprinted with permission from ref ( 22 ) Copyright 2022, American Chemical Society. …”

“…Similar results of DI and SW were achieved in a similar study. 22 From the figure, it can be concluded that Na 2 SO 4 is the source of viscosity reduction of the SW. Using the high pH increases the stability; however, the FTIR test performed by Kamal et al 15 showed that at higher pH, a reaction happens between the GLDA and the base.…”

Individual Seawater Ions’ Impact on the Rheology of Crosslinked Polymers in the Presence of a Chelating Agent

“…The second section examines the impact of varying concentrations of GLDA on the crosslinked polymer. The research was done by selecting just two concentrations (4 and 10 wt %) since the very high concentration had a detrimental effect based on our previous study . Finally, the optimized GLDA concentration was tested with the crosslinked polymer at different temperatures.…”

“…The CMHPG cationic polymer employed in these tests as a gelling agent has previously shown positive results when hydrated in DI and SW. 26 When the chain of CMHPG polymers absorbs water, it transforms from a compacted state to an extended-relaxed state named hydration. Since CMHPG hydrates quicker, is more stable at low pH, and degrades more slowly than competing polymers, it has widespread usage in fracturing fluids.…”