Interfacial and rheological investigation of enhanced oil recovery agents derived from Spirulina biomass

Abstract

This study investigates interfacial and rheological properties of novel, Spirulina-based fluids developed for potential use in enhanced oil recovery (EOR) applications. The purpose of this investigation is to determine the driving mechanism(s) behind the EOR performance of these materials after a previous study concluded that the EOR fluids are a promising technology with up to 96% recovery of the original oil in place (OOIP). It was then hypothesized that the EOR mechanism arose from the interfacial energy effects and/or the rheological properties. In this study, Arthrospira platensis (Spirulina) biomass is modified by different denaturants (sodium hydroxide, citric acid, and urea) and tested for a wide range of interfacial and rheological properties. The interfacial properties include surface tension, interfacial tension with hydraulic oil, contact angle against silicon dioxide, and work of adhesion between the fluid and the silicon dioxide surface. The rheology focuses on determining fluid viscoelastic properties and flow behaviors. Additionally, this study compares and correlates the results amongst each other, which also includes pH, EOR performance, and denaturant concentration.The EOR performance of these fluids strongly correlates with the increased viscosity, reduced interfacial tension (IFT), and increased wettability in the EOR fluids. All of the investigated EOR solutions reduced the IFT. Most of the EOR solutions were found to be mostly shear-thinning with shear-thickening approximately in the 2,000–5,000 s−1 range. From the results, it is concluded that the performance of the different types of EOR fluids is based on different mechanisms. Sodium hydroxide-based fluids are driven by increased low-shear viscosity, reduced IFT, alkaline pH shift, and improved wettability. The citric acid-based fluids do not exhibit high viscosity values in the low shear range, which indicates that their EOR performance seems to be driven by reduced IFT, acidic pH shift, improved wettability, and increased fluid rigidity by the generation of crosslinks in the macromolecular structure. Urea-based fluids did not exhibit improved viscosity, which means that their modest EOR performance is likely driven by reduced IFT and improved wettability. While a shear-thickening rheology is often considered to be a mechanism for improving EOR, it is concluded that the shear-thickening effect is not a dominant mechanism for these fluids, especially since the highest performing EOR fluid (highest NaOH concentration) did not display shear thickening.