Characterization and likelihood application of extracted mucilage from Hollyhocks plant as a natural polymer in enhanced oil recovery process by alkali-surfactant-polymer (ASP) slug injection into sandstone oil reservoirs

Abstract

Injection of water-based polymeric solutions into oil reservoirs is a common way to enhance oil recovery in the tertiary oil production stage. Polymers are normally injected under different scenarios individually, or with surfactants and alkalis, or both as a slug. Adjusting the ratio of water and oil mobility, preventing the phenomenon of fingering and early production of injectable water by increasing water viscosity are the most important mechanisms of polymer injection in enhanced oil recovery (EOR) process. In this study, the possibility of using extracted mucilage from Hollyhocks plant as a natural polymer for injection as a slug with surfactant and alkaline in sandstone reservoirs was investigated. The plant polymer was characterized by Fourier Transform Infrared Spectroscopy (FTIR), Energy Dispersive X-ray Analysis (EDAX) and Thermal Gravimetric Analysis (TGA) after extraction and preparation. Viscosity tests were performed at different shear rates and the effects of polymer concentration, polymer hydration time, temperature and salinity on the viscosity of the polymeric solutions were investigated. Finally, a polymeric slug containing the polymer, an anionic surfactant at the critical concentration of micelle (CMC) and NaOH alkali at the optimum concentration was injected into a sandstone plug to calculate the oil recovery rate by the Alkali-Surfactant-Polymer (ASP) slug injection process. The novelty of this research is the introduction and use of a new, affordable and inexpensive polymer for use in ASP-slug injection into sandstone reservoirs, which can solve many of the challenges in this method. Based on the results, TGA analysis confirms the stability of the polymer at reservoir temperatures. Decreased viscosity versus increased shear rate shows non-Newtonian behavior of the polymeric solutions. The viscosity values of the polymeric solutions are several tens of times more than the surfactant solutions viscosities even at the low concentrations. Therefore, the polymer can be considered suitable for use in the ASP-slug injection process. The viscosity of polymeric solutions decreases with increasing temperature and salinity. However, the final values are not low enough to counteract the polymer effect. Finally, an increase in oil recovery of 27.9% is achieved under the ASP slug injection process containing an anionic surfactant synthesized from waste chicken fat at CMC, NaOH alkali at 2500 ppm and the polymer extracted from Hollyhocks at 2000 ppm. At last, it should be mentioned that the main purpose of this study was to introduce a new polymer for EOR process by injecting ASP slug. However, its application does not lead to this only. Polymers are used in various oil and gas industries. Due to the properties and behavior of the polymer solution, it can be used to reduce water production from oil reservoirs, improve the properties of drilling fluids and inject it with other additives to increase oil recovery.