Smart Water as Wettability Modifier in Carbonate and Sandstone: A Discussion of Similarities/Differences in the Chemical Mechanisms

Abstract

Waterflooding has for a long time been regarded as a secondary oil recovery method. In the recent years, extensive research on crude oil, brine, and rock systems has documented that the composition of the injected water can change wetting properties of the reservoir during a waterflood in a favorable way to improve oil recovery. Thus, injection of “smart water” with a correct composition and salinity can act as a tertiary recovery method. Economically, it is, however, important to perform a waterflood at an optimum condition in a secondary process. Examples of smart water injection in carbonates and sandstones are: (1) injection of seawater into high temperature chalk reservoirs and (2) low salinity floods in sandstone reservoirs. The chemical mechanism behind the wettability alteration promoted by the injected water has been a topic for discussion both in carbonates and especially in sandstones. In this paper, the suggested mechanisms for the wettability modification in the two types of reservoir rocks are shortly reviewed with a special focus on chemical similarities and differences. The different chemical bonding mechanisms of polar components from the crude oil onto the positively charged carbonate and the negatively charged quartz/clay indicates a different chemical mechanism for wettability modification by smart water in the two cases.