The development of deepwater, high temperature fracturing fluids for continued operations in the most challenging offshore environments in the world led to the need for high performance scale inhibitor additives to be developed. Many conventional scale inhibitors were either not compatible with the fluid (typically due to chelation of the zirconium cross-linker) or were not thermally stable at 350°F or above.
The requirement was to have a scale inhibitor that could inhibit both carbonate and sulfate scales, even at the elevated pH found in the frac fluid system. The scale inhibitor also needed to be suitable for deployment into both sandstone and carbonate reservoirs and be able to protect the near wellbore from formation damage caused by the injected fluids. Furthermore, the scale inhibitor was required to provide ongoing protections to the formation after fracture fluid flowback by exhibiting favorable adsorption / desorption behavior. This unique combination of requirements meant a back to basics approach needed to be taken and structure performance relationships developed for the main types of classic scale inhibitor chemistry functional groups.
The test methods employed and chemistry of products tested are reported in this paper. Details of the hydraulic fracturing fluid compatibility testing highlight the significant effect the wrong choice of chemical can have on rheology over a range of temperatures. Performance testing shows the effect that even small concentrations of zirconium can have on scale formation and inhibition at elevated pH. Very enlightening SEM images and EDX analysis of the solids formed show a complex interaction between the scale inhibitor, zirconium concentration and pH.
The lessons learned from this development and case history will provide invaluable insights into the development of future fracture fluid packages, which are needing higher amounts of scale inhibitor as fracturing is occurring in more saline, higher temperature and pressure shale plays.