Evaluation of a New Liquid Breaker for Polymer Based In-Situ Gelled Acids

A solid breaker is used to reduce the viscosity of the gel at pH range of 4-5 for in-situ gelled acids with Zr4 cross-linkers utilize. However, the literature survey confirmed that solid breakers caused a premature reduction in the fluid viscosity resulting in a less than desirable productivity. Therefore, an effective liquid breaker that is based on tetrafluoroboric acid was developed.

This study was conducted to evaluate this new breaker system under the following conditions: breaker concentration (0-200 ppm), and acid injection rate (0.5-10 cm3/min).

The major findings from the performed viscosity measurements and single coreflood experiments can be summarized as follows: the crosslinking of the polymer occurred at a pH value of 1.8. At a pH of less than 2, doubling the breaker concentration did not affect the viscosity of the acid. However, at a pH of greater than 2, the viscosity of acid was reduced by 30 percent. At a breaker concentration of 0 ppm, the appearance of Zr in the core effluent sample was delayed by 0.25 PV compared to the reaction product, while at 100 ppm, Zr was delayed by 0.75 PV. At 200 ppm breaker, no Zr ions were detected in the effluent samples. Additionally, it was observed that as the breaker concentration increased, more Zr remained inside the core, as ZrF4, which is water-insoluble. Increasing the breaker concentration from 100 to 200 ppm reduced the final normalized pressure drop by 50 percent at injection rate of 2.5 cm3/min. Permeability reduction due to gel was reduced by increasing the acid injection rate.