Abstract
This paper reports the metal losses caused by an acid fracturing process carried out on a crude oil well completed with 22 Cr duplex steel. The composition of the acidizing fluid was formulated in order to protect the production tubing against corrosion, during the stimulation of a limestone reservoir. The fluid was formed by a strong acid, a weak acid, a surfactant and a commercial high temperature corrosion inhibitor.
The loss of metal in the production tubing was calculated from the iron, nickel and chrome concentrations in the produced fluid, once the well was open for operation. The total acid number was also measured in the same fluid samples used for the metal counts. In order to carry-out the calculations of corrosion rate, two different assumptions regarding the composition of the returning fluid were made. In both assumptions the acid was taken as the only aggressive fluid, the difference being in the aggressivity of the returning spent acid, and in the mixing inside the formation of the various fluids used during the stimulation job. The metal counts yielded a loss of production tubing, due to corrosion, in the range 0,035 - 0,040 Ib/sq. ft. during the operation. For both assumptions the evolution of the total acid number showed a reasonable agreement with the variation of the metal concentrations with time.
