A comprehensive review of polymers and their derivatives for enhanced oil recovery

The production of crude oil must be increased to fulfil the world energy demand. As the global need for energy is growing rapidly, oil will serve as the main energy source for next ∼30 years. This energy requirement can be attained through the application of enhanced oil recovery (EOR) technology into marginal wells or by exploring new oil fields. However, the world has reached to a point where the oil recovery from existing reservoirs is more economical than drilling new wells. As the traditional recovery methods are inefficient and less economically sustainable, EOR emerged as viable method to extract the residual oil (∼50 %) from existing mature reservoirs. Within EOR, biopolymers are gaining popularity in the oil industry because of their accessibility, cost-effectiveness, environmental sustainability, viscoelastic behaviour, and biodegradability. Biopolymers like Guar gum, Xanthan gum, Cellulose, Welan gum, Scleroglucan, Schizophyllan, and Gum tragacanth are expected to replace synthetic polymers. However, the main challenge for biopolymers are microbial deterioration and shear-stress stability. Factors like temperature, salinity, polymer concentration, and chemical functional groups significantly impact biopolymer efficiency. To improve these parameters several studies have been conducted for the development of modified polymers using methods like grafting copolymerization, esterification with acylants, nanocomposite functionalization, crosslinking, and hydrogel formation. Recently, chemo-selectively modified and thermo-viscosifying biopolymers have been developed to increase sweep efficiency under reservoir conditions. Modified polymers may enhance EOR performance by viscosity increment, wettability alteration and emulsification. This review discusses polymers used in laboratory and field studies, highlighting their application in EOR.