Chelating Agents as Scale Inhibitors for Seawater-Based Fracturing Fluids Under High-Temperatures and High-Salinity Conditions

Abstract Hydraulic fracturing frequently requires substantial amounts of fresh water, raising sustainability concerns. Substituting fresh water with seawater, despite its high sulfate content which can cause scaling, presents a viable alternative. This study aims to develop a seawater-based fracturing fluid that remains stable at high temperatures and precipitate-free. The focus is on evaluating compatible chemicals to develop an effective formulation using synthetically prepared seawater. Commercial scale inhibitors, including polymeric-based and phosphonate-based types, along with chelating agents such as GLDA, DTPA, and EDTA, are evaluated for scale prevention through static bottle tests. These tests use a 1:1 mix of synthetically prepared seawater (TDS 58,850 ppm) and synthetically prepared formation water (TDS 274,740 ppm) to evaluate the incompatible ions and their impact on scale inhibitors. Concentrations range from 1.0 wt% to 0.1 wt% to identify the minimum effective dose. Solution conductivity before and after treatment were measured to assess efficacy, while scanning electron microscopy examines precipitated mineral morphology. The tests are conducted at 158°F and 338°F, evaluating the inhibitors performance and thermal stability under extreme conditions. When synthetically prepared seawater and formation water were mixed without any inhibitors, precipitates of calcium sulfate, strontium sulfate, and sodium chloride formed under the tested temperatures. The higher temperature of 338°F accelerated precipitation compared to 158°F. The findings suggest that a minimal concentration is sufficient to effectively prevent scaling in high-salinity environments at both 158°F and 338°F over a seven-day testing period. All the tested chelating agents only required the lowest concentration (0.1wt%) to prevent scale formation at 158°F, outperforming the commercial scale inhibitors. Notably, DTPA was the only agent that effectively prevented scale at 338°F, also at the minimal concentration of 0.1wt%. This low concentration requirement not only ensures effective scale prevention but also addresses cost challenges associated with developing raw seawater-based fracturing fluids. This research not only advances the potential for more sustainable hydraulic fracturing practices by reducing dependence on fresh water but also addresses the critical challenges associated with the use of seawater, paving the way for more environmentally fracturing operation, and potentially saving millions of gallons of fresh water.