Abstract
In low-permeability reservoirs, more than half of the pore channels do not participate in filtration and the oil is blocked due to the small pore size. If the reservoir is water wet, this oil can be recovered by initiating capillary water impregnation by injecting water into the production well, but the efficiency of increasing the oil recovery factor may not increase significantly or may be reduced due to a decrease in oil phase permeability. In case of oil wet reservoir, it is necessary to apply surfactants optionally. It is known that surfactants are perspective methods for mobilization of residual oil in cEOR by means of decreasing surface tension at the water/oil phase boundary and by changing wettability of reservoir rock from oil wet to water wet.
Anionic surfactants are the most widely used type of surfactants in cEOR because most of the cEOR work has been conducted in sandstone reservoirs. The relationship between anionic surfactants and sandstone is related to adsorption and surface charge. Anionic surfactants are negatively charged same as the surface of sandstone, this helps to reduce adsorption on the rock. The adsorption of anionic surfactants on the sandstone surface can alter its physicochemical properties such as surface tension and wettability.
Anionic and non-ionogenic surfactants on a laboratory scale under conditions of high temperature and high salinity have been investigated. The selection of a suitable surfactant is a difficult task, and surfactants must be evaluated using a combination of screening methods. International studies show that most surfactant flooding has been conducted in low-temperature and low-salinity sandstone reservoirs. However, high-temperature and highly mineralized reservoirs are still challenging reservoirs for surfactant flooding.
