Wettability alteration in carbonate and sandstone rocks due to low salinity surfactant flooding

Abstract

Commonly, desorption of crude oil from rock surfaces accomplished by the exposure to the decreasing salt concentrations of NaCl, Na2SO4, MgCl2 and CaCl2 solutions. However, adsorption and desorption of crude oil are the functions of several attributing factors at undoubtedly low salinity brine solutions. For silica surfaces, both rock and oil possess negative charges during low salinity injection that leads to the electrical double layer expansion and electrostatic repulsion between them. For carbonate rocks, rock dissolution and negatively charged surface at higher pH could be regarded as the driving forces for oil desorption. Thus, adsorption/desorption studies of different oils over silica and carbonate rocks while considering salinity, ion composition and aging of the rocks would be sufficient to alter the wettability of the rocks. In the present paper, the effect of saline water containing surfactant has been discussed on the performance of enhanced oil recovery (EOR). Wettability alteration triggered by the change in interfacial tension (IFT) between crude oil and low salinity surfactant (LSS) is known to be the main factor regarding EOR processes. However, wettability depends on several factors, namely, multiple ion exchange (MIE), interfacial elasticity modulus, cation bridging, acid/base numbers of oil, rock composition and structure, ratio of divalent/monovalent (M2+/M+) cations in the formation brine, aging time, the status of zeta potential, surfactant structure and concentration, pH of the medium, T & P of reservoir, permeability and pressure drop change. Therefore, we thoroughly examine the microscopic mechanisms of LSS flooding via studying individual aforementioned factors that influence the contact angle change in sandstone and carbonate rocks.