High-density completion brines are widely used in well completion and workover operations. However, these high-density brines are susceptible to iron contamination and thus must be treated for iron removal. In particular, high-density brines containing zinc are the most difficult to treat for iron removal due to their relatively low pH.
Multiple approaches and technologies have been used for brine reclamation, including the use of an oxidizing agent such as peroxide. Unfortunately, conventional reclamation processes using peroxide usually require multiple steps, significant chemical additions, long reaction times, and extensive filtration to remove the iron and the excess treatment chemicals. However, it has been observed that using a higher concentration of peroxide can quickly and effectively remove iron even from brines containing zinc.
This paper describes the effectiveness of various peroxide concentrations used to remove iron from zinc bromide and calcium bromide brines. In a laboratory experiment three concentrations of hydrogen peroxide (0.6%, 1.5%, and 3%) were tested for their ability to remove iron from these two brines over various time intervals. The 0.6% peroxide reduced the iron concentration in the zinc bromide brine by 24% in 48 hours. Increasing the hydrogen peroxide concentration from 0.6% to 1.5% resulted in a 98% reduction of iron in 48 hours. However, maximum effectiveness was achieved with a 3% hydrogen peroxide concentration, which reduced the iron by 100% in just 6 hours. Experiments performed on calcium bromide brine showed similar results.
A kinetic study shows that the reactions follow first order kinetics. From the standpoint of kinetics, we calculated the initial rate of reaction for each concentration of peroxide which proved that the reaction rate increased as the peroxide concentration increased. For the 0.6% hydrogen peroxide concentration, the calculated rate constant was 3x10-6S-1 with the half-life of 64.16 hr. For the 3% hydrogen peroxide concentration, the rate constant was calculated as 2x10-5 S-1 and with a half-life of 5.2 hrs. In addition, we calculated the activation energy for each of the reactions which are detailed in the paper.