Alkaline/Surfactant/Polymer Flooding With Sodium Hydroxide in Indiana Limestone: Analysis of Water/Rock Interactions and Surfactant Adsorption

Abstract

Summary We recently used sodium hydroxide (NaOH) in Indiana limestone coreflood experiments to lower anionic-surfactant adsorption. This study presents analysis of the limestone geochemistry and the surfactant adsorption under static and dynamic conditions. Analysis of the effluent ionic composition using ion chromatography and inductively coupled plasma showed the presence of sulfate (SO42−) aluminum (Al), and iron (Fe), as well as calcium (Ca) and magnesium (Mg). To determine the likely source of each geochemical species and to characterize how the dissolution kinetics changes the slug chemistry, PHREEQC was used to inverse-model Indiana limestone rock using the bulk X-ray-diffraction (XRD) mineralogical composition and the influent and effluent water chemistry. Results showed that all Indiana limestone cores contained anhydrite, which was not detected by XRD. The effluent concentration of Al increased with pH to approximately 15 mg/L, whereas Fe concentration remained fairly independent of pH at 0.04 ± 0.02 mg/L. These trends suggest the likely source of Al and Fe to be either clay dissolution or the release of natural clay colloids with NaOH. Simulations suggested that in Fe-bearing carbonates, alkali consumption is fast but limited with NaOH, which is observed as pH-front delay, whereas alkali consumption is slow but severe with sodium carbonate (Na2CO3) resulting in minimal pH-front delay but lower effluent pH compared with influent pH for prolonged injection times. Using the PHREEQC calculations, the ionic composition of the chemical slug in subsequent alkali/surfactant/polymer (ASP) experiments was adjusted. In addition, the coupled adsorption/transport of anionic surfactants in carbonate rocks was also investigated using surface-complexation-model adsorption under static and dynamic conditions. Model predictions agree with the single-phase-adsorption coreflood results and suggest that the adsorption on the metal oxides or clay could be comparable with that on calcite. This arises from the higher surface area and the point of zero charge of pH (pHpzc) of metal oxides.