Wettability Alteration of a Heavy Oil/Brine/Carbonate System with Temperature

The wettability of reservoir rock is a crucial factor controlling displacement efficiency and ultimate oil recovery. In this study, the wettability of carbonate reservoir rocks as a function of temperature has been studied by measuring the Amott index to water using an X-ray computed tomography (CT) scanner. The cores for the Amott test were carefully prepared and aged at reservoir conditions to achieve restoration of reservoir wettability. The reservoir cores contain dolomite and chert based on the results of Fourier transform infrared spectroscopy (FT-IR) and energy dispersive X-ray spectroscopy (EDS). The porosity, permeability, and saturation profiles were measured with a core-flooding system and an X-ray CT scanner. The wettability test was carried out at reservoir temperature (70–80 °C) and elevated temperatures (130 °C, 170 °C). The rock components were dissolved at elevated temperature (170 °C) and resulted in a slight increase of porosity and absolute permeability. Also, OOIP and Amott water index increased at elevated temperature. We infer that while the rock is mixed-wet to weakly water wet, it became more water-wet as the temperature increased. In addition, the zeta potentials between rock and brine were also measured under several pH and different solution conditions to corroborate inferences regarding the wettability of reservoir rock. Zeta potential measurement is consistent with a surface that is not strongly water wet under experimental conditions.