Influence of Surface Roughness on the Contact Angle due to Calcite Dissolution in an Oil–Brine–Calcite System: A Nanoscale Analysis Using Atomic Force Microscopy and Geochemical Modeling

Abstract

Low-salinity water flooding appears to be a promising means to improve oil recovery in carbonate reservoirs because of a wettability alteration process. Contact angle measurement is a direct approach to reveal the wettability alteration in an oil–brine–carbonate system. However, questions have been raised about using contact angle measurement to justify the wettability alteration. This is because the contact angle may be significantly affected by surface roughness variation in the presence of low-salinity water because of calcite dissolution during the contact angle measurement. To clarify the cause and effect of wettability alteration during low-salinity water flooding, we measured the contact angle on two calcite substrates with similar surface roughness (7 and 4 nm) in the presence of high-salinity water (1 mol NaCl + 0.01 mol CaCl2) and low-salinity water (100 times diluted high-salinity water). Moreover, we measured the surface roughness of the substrates before and after the contact angle measurements using atomic force microscopy (AFM). Furthermore, we performed a geochemical study to quantify the amount of calcite dissolution in the presence of low- and high-salinity brines and compared it with surface roughness measurements. Our contact angle and AFM results reveal that surface roughness increase due to calcite dissolution in low-salinity water plays a negligible role in the contact angle, rather confirming that oil–brine–rock interactions govern the system wettability. Furthermore, our geochemical study shows that low-salinity water only dissolves 1.16 × 10–4 mol/mol of calcites in low-salinity water during the contact angle measurement. We, therefore, eradicate the possibility that surface roughness variation due to calcite dissolution in low-salinity water would affect contact angle results. Consequently, we argue that contact angle measurement remains a valid approach to directly examine the wettability alteration process in low-salinity water flooding.

Response of Non-Polar Oil Component on Low Salinity Effect in Carbonate Reservoirs: Adhesion Force Measurement Using Atomic Force Microscopy

“…It is worth noting that we saturated the deionized water with calcite to prevent any effect on the new calcite surface during cleaning. Also, it is noteworthy that the surface roughness of the new calcite surface used in this work is in a range of 4 to 7 nm, which has been reported in our previous work [44].…”

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

“… 45 , 46 In a work by Al Maskari et al, 45 it was observed that surface roughness (∼17 nm) caused by calcite dissolution did not greatly influence the wettability alteration trends caused by low salinity water on calcite substrates. Rather, Al Maskari et al 45 proposed that the electrostatic interactions at the nanoscale were strong and served as the driver for the observed changes in calcite wettability. In further analysis aimed at increasing the surface roughness, Sari et al 46 observed that at higher roughness (∼945 nm), the wetting state of the calcite rock was affected.…”

Influence of pH on Acidic Oil–Brine–Carbonate Adhesion Using Atomic Force Microscopy

“…56,57 Our previous work shows a surface roughness with a range of 4−7 nm on a new calcite surface, which plays a minor role in adhesion forces. 58 To remove small calcite particles from the new calcite substrate, deionized water equilibrated with CaCO 3 was used to rinse all the new calcite surfaces.…”

“…In this research, we used Iceland Spar calcite crystal to represent carbonate substrate in the adhesion force experiments (AFM) and contact angle experiments. Prior to all the AFM and contact angle experiments, the Iceland Spar calcite crystals were cleaved to gain a new clean calcite surface, which can help to eliminate the impact of surface roughness on the results of the experiments. , Our previous work shows a surface roughness with a range of 4–7 nm on a new calcite surface, which plays a minor role in adhesion forces . To remove small calcite particles from the new calcite substrate, deionized water equilibrated with CaCO 3 was used to rinse all the new calcite surfaces.…”