Study of Cross-Linked Gel and Chelating Agent Compatibility in High Salinity Environments

The utilization of high-salinity water in hydraulic fracturing is recommended to promote a sustainable process. However, the high concentration of total dissolved solids (TDS) in seawater and produced water results in scales within the formation and affects the fracturing fluid viscosity. Chelating agents prevent scaling due to the interaction between the formation water and the saline fracturing fluids. This research tests the scaling tendency when saline water and formation water are mixed in a high-salinity environment. It also highlights the incompatibility issues appearing between some cross-linked gels and chelating agents and offers a solution to these issues. Five cross-linked gels prepared with cross-linkers obtained from different companies were examined: three zirconium-based cross-linked gels, one zirconium borate, and one borate cross-linker. Four types of low pH GLDA and DTPA and high-pH GLDA and DTPA chelating agents were tested in this study. We utilized the differential scale loop (DSL 4025) to evaluate the effect of these chelating agents with 67,000 ppm of TDS produced water and 241,000 ppm of TDS formation water. Employing the Anton Paar-MCR 302 rheometer, simple rheology tests were used to quantify the impact of chelating agents in the cross-linked gel viscosity. Low concentrations of the DTPA chelating agent prevented scale formation and showed the best performance in capturing ions on ICP measurements. Simultaneously, when 0.1 wt % DTPA was added to a 1 wt % zirconium-borate cross-linked fracturing fluid, the viscosity exceeded 2000 cP. The DTPA is compatible with cross-linked gels in high-salinity environments and exhibits low scale and stable viscosity values. The better combinations and concentrations of the fracturing fluids were suggested, following the comparison of the highest viscosity, lowest conductivity, and the lowest detected scale.