PHPA™ preflush is an oxidant that helps break up highly-gelled muds for easier displacement. Some drilling muds are extremely difficult to mobilize and displace under realistic well conditions. Displacement is particularly challenging when polymer-laden mud systems such as partially hydrated polyacrylate (PHPA) muds are used. PHPA preflush is typically run as a 5% solution that breaks down the backbone of polymers and reduces the effect of gelation, which can inhibit or prevent displacement of static mud in the annulus.
PHPA preflush, which is stored and transported as a solid, offers the following advantages at concentrations of 2% to 10%:
- It is safer to work with than comparable concentrated liquid systems.
- It has a shelf life of at least 1 year with less than 10% activity loss.
- Dissolving the preflush in water immediately produces a high-pH (10.0 to 10.5), low-concentration peroxide solution (typically 0.5%).
Additionally, the chemistry of PHPA preflush provides good surface-acting particle lifting. Adding a low concentration (0.1 to 0.5 gal/bbl) of a strong water-wetting surfactant such as Pen-88™ surfactant, Pen-5M™ surfactant, or Cleanbore A™ surfactant can enhance the performance of the preflush and help it penetrate the gelled layer of a drilling mud.
PHPA preflush can be used with PHPA muds and muds enhanced with PHPA or other polymers. The preflush can be applied to primary and remedial cementing operations.
For primary cementing, it can be used as a sweep before the cementing operation. It can also be used as a preflush ahead of conventional cementing spacers such as Tuned® Spacer fluid. In cases of severe gelation, PHPA preflush has successfully been run as both a circulation sweep and as a preflush. Volumes that provide 10 to 15 minutes of contact time are usually sufficient.
For remedial cementing, PHPA preflush can be used as a preflush, or as a breakdown fluid to clean out polymer mud channels before a squeeze job. To help ensure that solids released from the mud can be effectively carried out of the hole, the fluid (spacer or mud) following the PHPA preflush should have good solids-carrying capacity.