Wettability Alteration during Low-Salinity Water Flooding

Abstract

Low-salinity water flooding (LSWF) for hydrocarbon recovery has attracted industrial attention, owing to its simplicity and economic feasibility. Although this topic has received numerous studies, mechanisms driving the low-salinity effect remain poorly understood. This study is aimed at investigating the direct effects of injecting lowsalinity brine (0.6 and 0.2 M NaCl) as the non-wetting fluid and Soltrol 130 as a synthetic wetting fluid on outcrop "Austin Chalk" rock samples. The petrophysical properties of rock samples were estimated by saturating the core samples with high-and low-salinity brine at laboratory conditions. Experiments were conducted for unsteady-state and steady-state flow for both imbibition and drainage processes. A shift to the right has been observed for the relative permeability curve of 0.2 M NaCl along with a drop in irreducible water saturation (S wi ) and in residual oil saturation (S or ). Furthermore, the results have shown a reduction in irreducible water saturation from 22.2 to 18.7% when using 0.2 M NaCl compared to 0.6 M NaCl. The current research demonstrates that ionic interactions among rock, oil, and brine compositions would alter the in situ wettability of the carbonate samples from oil-wet/mixed-wet to more water-wet conditions. A correlation is found among the double-layer expansion, ζ potential, and wettability alteration during LSWF. Moreover, improved oil recovery takes place during LSWF only when a repulsive electrostatic force between oil−brine and mineral−brine interfaces is induced by the change in brine composition. ζ potential of the carbonate is found to become more negative with the dilution of the brine. After the sample is aged with oil, the ζ potential changed, indicating an alteration in wettability.

Calcite–Brine Interface and Its Implications in Oilfield Applications: Insights from Zeta Potential Experiments and Molecular Dynamics Simulations

“…71−76 This is further highlighted by the report of Al-Bayati et al 77 who described the changes in the carbonate rock samples and concluded that the observed recovery was caused by the electrical double layer effect brought on by the injected fluid's reduced ionic strength. Our findings further provide evidence to support the conclusions by Al-Bayati et al; 77 however, mineral dissolution as a governing mechanism is ruled out.…”

“…This lays the foundation for understanding the critical role the electrical double layer plays in the quest for mineral wettability control. Several mechanisms, including multivalent ionic exchange, electrical double layer (EDL) expansion, electrostatic bond interactions, surface charge alteration, and calcite dissolution, have been proposed in the literature to be responsible for the carbonate rock wettability. − This is further highlighted by the report of Al-Bayati et al who described the changes in the carbonate rock samples and concluded that the observed recovery was caused by the electrical double layer effect brought on by the injected fluid’s reduced ionic strength. Our findings further provide evidence to support the conclusions by Al-Bayati et al; however, mineral dissolution as a governing mechanism is ruled out.…”

Adsorption Study of Novel Gemini Cationic Surfactant in Carbonate Reservoir Cores—Influence of Critical Parameters

“…This confirms the retention of surfactants on the surface of the rock pores. Moreover, the post-injection deionized water may have caused the mineral dissolution of the carbonate core [ 37 ].…”

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

“…Multivalent ionic exchange, an EDL expansion, electrostatic bond interactions, surface charge alteration, and calcite dissolution are the wettability modification mechanisms connected with carbonate rocks. ,− This is highlighted in the report of Al-Bayati et al who described the change in the carbonate rock samples and concluded that the observed recovery was caused by the EDL effect brought on by the injected fluid’s reduced ionic strength. Thus, understanding the electrostatic interaction at the rock surface caused by the salinity and composition of the brine is necessary to understand these mechanisms.…”

“…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.…”