A New Shear-Tolerant High-Temperature Fracturing Fluid

Abstract

Abstract The extent of crosslinking a polymeric fracturing gel can significantly contribute to the success or failure of a hydraulic fracturing treatment. In certain cases, excessive crosslinking while the fluid is in the tubulars can result in friction pressures that are too high, and may prohibit the treatment from achieving the design goals. With titanium (Ti) or zirconium (Zr) crosslinked gels, which are known to be prone to irreversible shear degradation, early crosslinking in the tubulars can substantially reduce the final gel strength, even to the degree that near wellbore proppant transport is compromised, and the treatment may screenout. On the other hand, a Ti or Zr crosslinked gel which crosslinks substantially after exiting the perforations may not have sufficient proppant transport capability to complete the treatment successfully. Varying treatment conditions such as mixwater composition and temperature, tubular shear rate and transit time, and reservoir temperature pose difficult challenges to routinely achieving the optimal crosslinking state. Conditions such as offshore wellbore temperature profiles and viscous heating in smaller diameter tubing can further complicate the task. Various chemical means have been employed to tune the crosslinking temperature for specific treating conditions. These methods involve addition of chemicals to control the crosslinking kinetics, such as pH buffers, crosslinker concentration, and competing ligands to temporarily bind the metal crosslinker. Blended crosslinkers containing a single Group 4 (Ti, Zr) metal with different organic ligands with different binding strengths have been employed to achieve crosslinking at two temperature ranges so that early viscosity for proppant transport can be developed. Mixed metal crosslinkers, such as aluminum and Zr have also been formulated for this same purpose. This paper examines the disadvantages of these strategies, and describes the development and deployment of a high-temperature fracturing fluid system that has shown to overcome those issues.