الملخص الإنجليزي
Enhanced Oil Recovery (EOR) plays a key role in maximizing oil extraction from mature
fields. Engineered water (EW) treatment emerged as a promising, cost-effective, and
environmental-friendly EOR approach. The main objective of this laboratory study is to
elucidate how varying the concentrations of the potential determining ions (PDIs) and
temperature affect the wettability of dolomite during the EW injection process and explore
the underlying mechanisms that lead to wettability alteration.
The wettability alteration of dolomite surfaces was assessed using contact angle
measurements. EW solutions were prepared using Ca2+, Mg2+, and SO4
2-
, individually and
in combinations. Different concentrations of PDIs were considered (0.001, 0.01 and 0.1
M). The tests were carried out at different temperatures (25, 50, 75, 100 and 125 °C). The
PDIs’ concentrations before and after contacting dolomite minerals were measured using
Ion Chromatography (IC) and Inductive Coupling Plasma (ICP), in order to gain valuable
insights into the mechanism responsible for wettability alteration.
Results showed a noticeable reduction in the contact angle of the dolomite surfaces after
treatment with EW composed of individual PDIs at temperatures > 75 °C. At 25 and 50
°C, there was minor to no change in contact angles after treatment with EW systems. SO4
2-
alone was able to alter the wettability of the surface toward water-wet due to the adsorption
of the SO4
2- on the positively charged dolomite surface. In terms of combined PDIs
systems, the results revealed that altering the concentrations could affect the wettability
alteration performances at different temperatures; contact angle could increase, decrease
or pass by a minimum with increasing temperature. Best wettability alteration toward
water-wet state was achieved when combining the lowest concentration of Ca2+ and SO4
2-
and (0.001 M) with the highest concentration of Mg2+ (0.1 M) at the temperature of 125
°C. The concentration of PDIs before and after treatment indicates a decrease in SO4
2-
levels. This is because the presence of SO4
2- boosts the reaction between the ions (Ca2+
and Mg2+) and dolomite surface, and decreases hydrogen bonding that lead to partial
removal of carboxylate. When the concentration of Mg2+ increases in the prepared EW,
the effect of Mg2+ becomes more pronounced with the presence of low Ca2+, while the
increase in the concentration of Ca2+ causes precipitation. IC and ICP analysis indicate
that multi-ion exchange and mineral dissolution play a major role in wettability alteration.
These findings demonstrate that EW treatment, with optimum PDIs concentrations, can
effectively modify the wetting properties of dolomite surfaces. However, as observed in
the experiments, the potential for carbonate precipitation requires carefully balancing ion
concentrations to prevent negative impacts on reservoir characteristics.
This study provides a deeper insight into some of the underexplored controlling factors of
dolomite wettability alteration. These factors include concentration thresholds, detailed
mechanistic insights, and practical implications for EOR.
