Effect of Ionic Strength on the Interfacial Forces between Oil/Brine/Rock Interfaces: A Chemical Force Microscopy Study

Abstract

The presence of thin aqueous films and their stability have a profound effect on the interactions between oil/brine/rock interfaces. In a previous report, we proposed that hydration forces, originating from the overlap of hydrated layers of different surfaces in the presence of sodium chloride, played an important role at short range. In the present work, divalent ions were introduced to the liquid films and, the mechanisms in improving oil recovery from low-salinity brine and the low-salinity effect at the molecular level were revealed. Through a direct force-measuring technique of chemical force microscopy (CFM), the functionalized atomic force microscopy (AFM) tips felt a solid surface to mimic the oil/rock interactions in brine. It was found that not only did the van der Waals and electrostatic forces have a great effect on this process due to the interactions between the charged interfaces of oil/water and water/solid, but also some important additional interactions appeared at short range under a variety of salinity concentrations or compositions. Taking into account the important role of structural forces under a small distance, the force profiles were fitted well with the theory of extended Derjaguin–Landau–Verwey–Overbeek (denoted by EDLVO) through a double-exponential or Gaussian model. Interestingly, low adhesion appeared in the presence of sodium sulfate, because hydration forces contributed to the resultant force depending on the intrinsic properties of the solvent or solute molecules, while in the presence of calcium chloride, high adhesion emerged due to the dispersion interaction between water and hydrocarbon molecules, as well as the reorientation or restructuring of water molecules with tiny breakage of hydrogen bonds. Therefore, on the basis of the EDLVO theory, additional forces were suggested to play an important part in short range, proposing a better understanding of the effect of divalent ions on the thin liquid films in the process of increasing oil recovery.

Extended DLVO-based estimates of surface force in low salinity water flooding

“…However, all above mentioned studies have been carried out from core-scale to reservoir-scale. While the atomic force microscopy (AFM) [28,29] and quartz crystal microbalance with dissipation (QCM-D) [30] were used to investigate the effect of water chemistry on adhesion force, few have investigated correlation of nano-scale mechanism(s) of wettability alternation and core-scale experimental results, and fewer have looked beyond the simple and practical approach to guide industry to engineer the injected water chemistry, thus improving oil recovery based on disturbing the in-situ thermodynamic equilibrium. Our objectives were to gain better understanding of low salinity water flooding in nano-scale by addressing the following questions:…”

Organic-Silica Interactions in Saline: Elucidating the Structural Influence of Calcium in Low-Salinity Enhanced Oil Recovery

“…More specifically, our data can be compared with previous CFM studies of the adsorption of other functionalities at the aqueous electrolyte/model sandstone interface. The adhesion of an alkyl-terminated tip at the aqueous electrolyte/mica interface was dependent on both NaCl and CaCl 2 concentration 19 . A low-salinity response was also observed for a COOH/COO − functionalized tip at an amorphous silica surface in artificial seawater: at high salinity (36,500 ppm), adhesion was 46 pN compared with 33 pN at low salinity (1400 ppm) 12 .…”

“…The chemical force mapping mode (CFM) of atomic force microscopy (AFM) can be used to determine adhesion force. CFM experiments showed that the adhesion of an alkyl-terminated tip to mica was ~23× stronger in aqueous CaCl 2 than in aqueous NaCl at three different concentrations (10 mM, 100 mM and 1000 mM) 19 . In contrast to previous studies 16 , 17 , the adhesion depended on the concentration of NaCl.…”

Molecular interactions between DOPA and surfaces with different functional groups: a chemical force microscopy study

“…In the present paper, DLVO theory was extended to provide a more complete interpretation of force-distance experimental data, as expressed in eqn 7: 38,46,47…”