Abstract:

To meet the application requirements of seawater-based fracturing fluid for delayed crosslinking and high temperature resistance, a series of seawater-based fracturing fluids applicable in different temperature range were formulated by optimizing the ratios among salt-resistant guar gum, high-temperature crosslinking agent, etc., achieving controllable crosslinking time at low pH and a maximum temperature resistance of 180 ℃. The crosslinking process of fracturing fluids was tested through steady-state shear rheological experiments, and a 4-parameter rheological kinetic equation was used to fit the data. The effects of crosslinking agent concentration, chelating agent concentration, shear rate, and temperature on the crosslinking process were analyzed. Both increasing the concentration of crosslinking agent and increasing the crosslinking temperature could accelerate the crosslinking process and enhance the strength of the crosslinking system; there were optimal ranges for both shear rate and chelating agent dosage in the crosslinking process. The crosslinking mechanism was further analyzed by measuring the microstructure of cross-linked gel and the elemental content during the crosslinking process. The difference in particle size and the different coordination number between boron and zirconium in crosslinking agents could affect crosslinking time and gel network structure, achieving delayed crosslinking, high crosslinking strength at low temperature, and improved temperature resistance through secondary crosslinking for seawater-based fracturing fluids.

Key words: seawater-based fracturing fluid, high-temperature resistance, high-temperature crosslinking agent, crosslinking kinetics, crosslinking mechanism