A Novel Approach to Improve Acid Diversion Utilizing In-Situ Foam Generating Fluids

Abstract Acidizing is a common stimulation treatment in carbonate reservoirs. Acid distribution over all layers and areas around a treated well is crucial for the matrix stimulation success. Effective acidizing, especially for long horizontal wells, requires acid diverting technique to insure uniform distribution along the wellbore intervals. Mechanical diversion is costly, while chemical diversion using in-situ gelled acid and viscoelastic surfactants have widely been applied during matrix stimulation. These chemical methods showed not only limited efficiency, but can introduce damage to the treated formation. Several chemical additives and complex formulations usually are used to ensure stability and success of diverting fluid application. This exercise greatly increases the treatment cost. This study introduces a novel solution to improve acid diversion using in-situ foam generation. Thermochemical fluid is used to generate foam in-situ at downhole conditions, which will divert acid stages into not treated sections of the reservoirs. In this paper, two field treatments of two water injector wells, a vertical and a horizontal, were demonstrated using the new system. The in-situ foam generating fluid was used to divert acid in several pumping stages to ensure homogenous treatment. Pumping sequence and treatment mechanisms were described. The results showed that in-situ foam generation approach has a very effective performance in diverting acid, with superior results compared to conventional diversion using viscoelastic surfactants. As the new system generates foam downhole, it showed very practical operation procedures. No pumping difficulties are experienced, compared with surface pumping to the foam. Having the reaction activated downhole, made the whole treatment safe and friendly to apply. Foam can occupy large areas, so less fluid is required to divert acid stage. Moreover, no complex formulation was required with several additives to ensure fluid activation downhole, which significantly reduced the overall treatment cost. The novel method will enable effective and homogenous acidizing of carbonate reservoirs and eliminate the need for viscoelastic surfactants, which is expensive with limited effect. This work presents an effective method to place acid uniformly across a treated well using in-situ foam generation.