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

Abstract

Wettability alteration seems to be the main physicochemical process during low salinity water injection in carbonate formations. A pH increase due to calcite dissolution during low salinity water injection may affect oil−brine−rock interaction and thereby wettability. However, far too little attention has been paid to quantifying the impact of such an pH increase on acidic oil− carbonate adhesion. Therefore, we measured contact angles between acidic oil (−COOH) and calcite crystal in the presence of 10 000 ppm NaCl solutions at different pHs (6.5, 9.5 and 11) at ambient conditions. Furthermore, we used atomic force microscopy (AFM) to measure the adhesion force between acidic oil groups (−COOH) and calcite substrate at different pHs (9.5 and 11) at similar conditions of the contact angle experiments. Moreover, to confirm the contact angle and AFM results, we measured the zeta potential of acidic oil−brine and calcite−brine interfaces at the same condition and calculated the thermodynamic isotherm disjoining pressure. Our results show that the contact angle reduces from 134 to 95°as the pH increases from 6.5 to 11, increasing hydrophilicity. Adhesion force measurements show that increasing pH reduces the adhesion force between the acidic oil and carbonate in line with contact angle results. Zeta potential results show that increasing the pH increases the negativity of the zeta potential of acidic oil−brine and calcite−brine interfaces, implying the increase of the electrical double layer force. Furthermore, the total disjoining pressure isotherm becomes less negative with increasing pH, implying an increase of hydrophilicity. Taken together, our results confirm that a local pH increase due to calcite dissolution during low salinity water injection would prevail in the wettability alteration process in particular for high acidic oil bearing carbonate reservoirs.

Environmentally Friendly Nanocomposite Functionality of Improved Oil Recovery (IOR) in Unconventional Reservoirs

“…Practically, electrostatic interplays between oil portions and reservoir rock are the mechanisms behind oil wettability in plenty of cases . Potentially, the enhancement of the electrical double layer could be the further mechanism that may modify the wettability of the shale surface through LSW (Figure d). , To be more precise, the distance between the carboxylate (R–COO – ) oil species and the rock surface increases by reducing the salinity of water due to the expansion of the electrical double layer and consequently detaches the carboxylate (R–COO – ) oil species and increases the oil recovery . This can be illuminated by the concept of Debye layer length, which is stated by the underneath eq K − 1 = true( ε r ε 0 K B T 2 N A e 2 I true) 1 / 2 where K –1 is the length of the Debye layer, ε 0 is the permittivity of free space, ε r is the dielectric constant, K B is Boltzmann’s constant, T is the absolute temperature in Kelvin, N A is Avogadro’s number, e is the initial charge, and I is the ionic strength.…”

“…They realized that by increasing the pH of the brine, the adsorption of oil on the rock surface decreases and, therefore, the hydrophilicity of the rock surface increases. 37 In conclusion, different mechanisms can be considered to improve the contact angle in low-salinity water injection. Thus, in this research, in addition to the effects of rock dissolution on improving wettability, an increase in fluid concentration causes an increase in pH level (Figure 7 in the Supporting Information part) and electrical conductivity (Figure 8 in Supporting Information part), so these two factors also can be considered as effective factors in improving the contact angle (Figure 2).…”

“…38 Potentially, the enhancement of the electrical double layer could be the further mechanism that may modify the wettability of the shale surface through LSW (Figure 3d). 23,37 To be more precise, the distance between the carboxylate (R−COO − ) oil species and the rock surface increases by reducing the salinity of water due to the expansion of the electrical double layer and consequently detaches the where K −1 is the length of the Debye layer, ε 0 is the permittivity of free space, ε r is the dielectric constant, K B is Boltzmann's constant, T is the absolute temperature in Kelvin, N A is Avogadro's number, e is the initial charge, and I is the ionic strength. By referring to this equation, an inverse relationship between the length of the Debye layer and the ionic strength is observed.…”

Effects of the Reservoir Environment and Oilfield Operations on the Iron Mineral Surface Charge Development: An Insight into Their Role in Wettability Alteration

“…The injection of ion-engineered water or low-salinity water (LSW) into the reservoir for improved recovery has gained attention over the decade with efforts dedicated to understand the mechanism responsible for the observed improvements. The different mechanisms postulated include wettability alteration, mineral dissolution, multi-ion exchange, double-layer expansion, and so on. − Several studies cover carbonate and sandstone formations with less attention being paid to their effects on iron minerals and clay. Thus, this section of our study aims to understand the role of ion-engineered fluid in the iron mineral surface charge development.…”

Effect of Sulfate-Based Scales on Calcite Mineral Surface Chemistry: Insights from Zeta-Potential Experiments and Their Implications on Wettability

“…The effect of both brines has gained significant attention recently and continues to be an active area of research. Several studies are available in the literature on smart and LSW effects on reservoir wettability and oil recovery. ,,− For example, using AFM and contact angle and ζ-potential measurements, Al Maskari et al described the impact of pH (caused by mineral dissolution in LSW) on carbonate surface wettability. Findings indicated that the contact angle decreased as pH increased, and this observation was corroborated by an increase in magnitude of the negative surface charge under the same circumstances.…”