Wettability Estimation by Oil Adsorption Using Quartz Crystal Microbalance with Dissipation QCM-D

Abstract The wetting properties of the reservoir rocks are governed by the tendency of the individual minerals constituting the reservoir rock to adsorb oil during crude oil/brine/rock (COBR) interactions. To explore the oil adhesion kinetics during COBR interactions, one approach is to assess the oil adhesion tendencies of the individual minerals. The aim of this presented study was to characterize the wettability by determining the oil adhesion tendencies of the minerals using Quartz Crystal Microbalance with Dissipation (QCM-D). The kinetics of the mass (Δmads) and the thickness (Δt) of the adsorbed film were modelled mathematically using the Sauerbrey relation with the QCM-D output as input. In addition, we present Surface Complexation modelling (SCM) evaluation of possible electrostatic linkages of the studied COBR system. The kinetics of oil adsorption during COBR interactions were prominent during Formation Water (FW)/Stock Tank Oil (STO)/FW injection sequence with kaolinite sensor as compared to that of quartz. This was depicted by the relatively high change in the FW frequency signal (Δf) before and after the injection of STO with kaolinite sensor as compared to quartz. Negligible change in the frequency signal (Δf≈ 0) was observed during the various injection sequence with quartz sensor. This suggested that minor adsorption has taken place, thus confirming the hydrophilic nature of the quartz sensor. The mathematical modelling of the thickness (Δt) and the mass (Δmads) of the adsorbed film also reveals that kaolinite is more oil wet than quartz. This is portrayed by the relatively high magnitude of the adsorbed oil on kaolinite (Δt = 6nm - 14nm and Δm = 1600ng - 3500ng). The SCM results also confirm negligible (≈ 0.008) electrostatic pair linkage for the quartz sensor as compared to kaolinite (≈ 0.3). This shows that the tendency for oil to be adsorbed onto kaolinite sensors were relatively high as compared to quartz. The electrostatic pair linkages reveal that the dominant electrostatic pair linkage existing between the mineral- brine and the oil-brine interface was cation bridging by divalent cations such as Ca2+ and Mg2+. Hence, it was not surprising that the FW/STO/FW injection sequence for all the three (3) methods were relatively oil-wet as compared to similar sequence of optimum LSW composition. This was attributed to the abundance of Ca2+ and Mg2+ to bridge the two negatively charged surfaces in the former than in the latter.