Investigating Integrated Chemical Treatments for Iron Oxide Removal in Water Injection Operations

Abstract

Abstract Quality of water used for injection is a very essential factor in preventing/minimizing formation damage potential due to scale precipitation. Various components in produced water such as H2S, suspended solids, bacteria and other metal ions such as iron are the primary cause of permeability impairment. Injected water should be compatible with both rock and formation fluids, thus the need to find chemical solutions to minimize the impact of injection water on formation rock arises. Potassium Permanganate (KMnO4), and Citric Acid based treatments are experimentally investigated to effectively improve water injection quality and minimize formation damage. Extensive experimental methods were conducted to determine the optimum treatmentpercentage required to reach optimum water quality, with least amount of scale precipitants. Water samples with high salinity, iron content, sulfates and bicarbonates were used in this study. Additional experimental methods including HT/HP compatibility tests and coreflooding experiments were conducted to evaluate the impact of adding KMnO4 and Citric Acid onformation water and formation rock permeability. Compatibility and coreflooding tests were conducted on different water mixtures to optimize a water mixture having less damage on formation permeability. Experiments were conducted at temperatures up to 250°F and pressure 3,000 psi. Post treatment damage mechanisms were also investigated using XRD and ESEM methods on formed scale due to fluid/fluid and rock/fluid interactions. The experimental investigation yielded that KMnO4 would reduce the iron content, therefore, eliminating possibility of formation damage. Oxygen scavenger was also added to some water mixtures to halt iron precipitation. HT/HP compatibility test results indicated that no iron oxide precipitation occurred in examined water mixtures after KMnO4 and oxygen scavenger were added. Coreflood experiments showed no permeability reduction in the core plugs although with white solid precipitation noticed on the face of the plugs which was attributed to the precipitation of the insignificant amount of CaCO3 as indicated by ESEM and XRD analysis. Citric acid-based recipe, on the other hand, yielded varying results with different water samples. Some cases showed somehow good water quality improvements with low iron content and others did not with high iron content. This paper presents an experimental approach to treating and optimizing the quality of water intended for injection using KMnO4, or Citric Acid. XRD, ESEM analysis and compatibility and coreflooding experiments were conducted to assess impact of interaction of different water/water mixtures on clastic and carbonate core plugs permeabilities. It also investigates different formation damage mechanisms associated with water injection.