Technical Committee Reservoir Engineering

Methods for a controlled degradation of fracgels in oil- and gas wells

Previous experience in frac operation demonstrated that the use of fracgels often leads to an incomplete fracgel recovery and therefore to a decreased productivity of the stimulated well. It is assumed that insufficient degradation of the fracgel caused by poor activity of the breakers leads to a decrease in productivity.

The aim of this work was the determination of effective breakers for the use in oil and gas wells to enhance the degradation of polymer fracgels. The investigations were carried out with Guarbased fracgels. These gels consisted of Guar or Hydroxypropyl-Guar both crosslinked with Borax (low-temperature (NT) gels) as well as Zirconium-crosslinked Carboxymethyl-Hydroxypropyl- Guar (CMHPG; high-temperature (HT) gels).

The work covered polymer analytical investigations, comprehensive rheological investigations of fracgels i.e. variation of pH-value, temperature, electrolytes (Li+, Na+, K+) as well as degradation studies with different breakers. The decrease of the pH-value led to a total destruction of the NT-gel network. The presence of electrolytes led to a rapid contraction of the gel forming a solid phase (syneresis). In degradation experiments, contracted Guar-Borax gels were successfully treated with acids, enzymes and high concentrated oxidative breakers at T = 60°C. HTGels (CMHPGIZirconium) were only partially degraded at increased temperatures with an oxidative breaker, whereas at T = 150°C a complete thermal degradation was observed.