Macro- and Microscopic Studies of “Smart Water” Flooding in Carbonate Rocks: An Image-Based Wettability Examination

Abstract

To date, numerous studies have shown that “smart water” flooding can enhance the oil recovery of carbonate reservoirs by altering the rock wettability. In particular, the Ca2+, Mg2+, and SO4 2– ions in smart water play important roles in altering the wettability of carbonate rocks, although their symbiotic effects are still under debate. In this study, we employ both macro- and microscopic methods, including ζ-potential measurements, contact angle measurements, and micro X-ray computed tomography (μ-CT) scanning to examine the effects of several “smart waters”, e.g., increasing SO4 2– concentrations or decreasing Ca2+ and Mg2+ concentrations in seawater, in changing the wettability of Austin chalk. ζ-potential results confirm that the surface potentials of chalk samples become more negative in smart waters than in seawater. Contact angle results suggest that smart waters are more effective in making the chalk surface more water-wet than seawater. However, seawater with four times the SO4 2– concentration (SW4SO) and seawater with one-fourth of the Ca2+ concentration (SW0.25Ca) show more potential in enhancing the alteration of chalk wettability compared to other smart waters. The μ-CT images offer a microscopic view of the fluid distribution in the porous media of chalk samples after flooding with seawater and followed by SW4SO or SW0.25Ca, which shows that SW4SO contributes to the increase in water-wetness in nanopores (or subscale porous structure), whereas SW0.25 contributes to the increase in water-wetness in micropores. In addition, the “effective contact angles” of chalk samples decreases approximately 10° after SW4SO and SW0.25Ca flooding, resulting in an increase in the “microscopic oil recovery” by 18.6 and 20.2%, respectively. Thus, this result suggests that SW0.25Ca is more effective in enhancing the water-wetness of chalk samples than SW4SO.

Ionic Interactions at the Crude Oil–Brine–Rock Interfaces Using Different Surface Complexation Models and DLVO Theory: Application to Carbonate Wettability

“…Therefore, seawater brine with low Mg 2+ and high SO 4 2– concentration would trigger high repulsive interaction energy and hence alter carbonate rock wettability toward water wetness. The observation herein was consistent to contact angle measurements performed by Ding et al 100 using the same brine composition. Ding et al 100 observed that a decrease in Mg 2+ concentration impacted the wettability alteration process that an increase in SO 4 2– concentration.…”

“…The observation herein was consistent to contact angle measurements performed by Ding et al 100 using the same brine composition. Ding et al 100 observed that a decrease in Mg 2+ concentration impacted the wettability alteration process that an increase in SO 4 2– concentration. SW0.25Mg resulted in the contact angle of 85.3° as compared to the SW4S measuring contact angle of 98.6°.…”

“…It should however be noted that mineral oil instead of crude oil was used for the contact angle measurement. 100 The adsorption of ions toward the oil–brine interface when using mineral oil remains unknown and hence was not modeled using the TLM-based SCM. Nevertheless, the trends of the effect of Mg 2+ and SO 4 2– ions on carbonate wettability in the work by Ding et al 100 were consistent with the total interaction potential calculated herein.…”

“… 100 The adsorption of ions toward the oil–brine interface when using mineral oil remains unknown and hence was not modeled using the TLM-based SCM. Nevertheless, the trends of the effect of Mg 2+ and SO 4 2– ions on carbonate wettability in the work by Ding et al 100 were consistent with the total interaction potential calculated herein. It should be noted that both Mg 2+ and SO4 2– ions have the potential to form scales and damage the reservoir formation.…”

Synergistic effect of salt ions and water‐soluble amphiphilic compounds of acidic crude oil on surface and interfacial tension

“…[ 1–10 ] The modification of the ionic composition of water can be examined by reducing the salinity of the injected water, reducing some monovalent ions such as Na + and Cl − , or increasing some divalent ions such as SO 4 2− Ca 2+ and Mg 2+ . [ 11–15 ] These modifications can enhance oil recovery by changing fluid/fluid and fluid/rock interactions. In general, wettability alteration, fine migration, double layer expansion, and reduction of interfacial tension (IFT) are known as the most prominent mechanisms.…”