Water-soluble chitosan polymer for enhanced oil recovery in the carbonate reservoir

Numerous surfactants, nanoparticles and polymers have been developed and utilized for enhanced oil recovery applications, irrespective of their environmental impact. Most of these oilfield chemicals were prepared through multi-steps from fossil-based starting materials using hazardous solvents. However, there is a desire to advance eco-friendly and sustainable materials to reduce CO₂ emissions and enhance the sustainability of oil production. Herein, we propose the development of chitosan salt, a solely green polymer, prepared in water in the presence of acetic acid (0.1% v/v). The resulting water-soluble polymer demonstrated excellent stability under reservoir conditions and was tested for enhanced oil recovery in the carbonate reservoir. The oil-wet rock wettability was significantly reduced after using chitosan salt solution. Nuclear magnetic resonance (NMR) experiments were used to show the oil displacement at different pores regions using relaxation time (T₂ distribution). Imbibition and coreflooding experiments showed that the chitosan salt is able to increase the enhanced oil recovery by extra 16.2% which surpass the recovery obtained from commercial surfactants such as α-olefin sulfonate (AOS) and cetrimonium bromide (CTAB). This study shows that green materials are promising candidates for oil recovery and upstream applications.