Wettability Change Related to the Adsorption of Organic Acids on Calcite: Experimental and Ab Initio Computational Studies

Abstract

We have investigated the interactions between organic acids and a calcite powder by adsorption from an organic phase (benzoic acid and lauric acid in toluene) and from an aqueous phase (benzoic acid and lauric sodium salt. In addition to the experimental study, ab initio quantum chemistry calculations were performed for cluster models, simulating the interactions of molecules with calcite surface sites. At the toluene/calcite interface, acids chemisorb on surface calcium ions, replacing surface hydroxyls resulting from the previous surface hydration by water. This surface saponification phenomenon was predicted by ab initio calculations and confirmed by spectroscopic techniques. The adsorbed acids conferred a hydrophobic character to calcite, with the higher contact angles in water for the longest alkyl chains in the organic acid. At the water/calcite interface, organic acids do not displace water. As electrostatic forces determine the stability of thin water films between calcite and crude oils at reservoir conditions, from our calculations, we deduce that when crude oil fills the biggest pores of the reservoir rock, oil/calcite interfaces appear where the adsorption of organic acids can change the wettability to oil-wet. By contrast, the mineral should remain water-wet at places where the capillary pressure has not been able to thin the aqueous phase beyond a critical value at which the film would collapse. This can occur even if the aqueous phase contains dissolved organic acids transferred from crude oil. Mixed wettability patterns might therefore be related to the spatial distribution of pore sizes. Our results support the latter conclusion in the specific case of organic acids with calcite. P. 889

Cost Effective Surfactant Formulations for Improved Oil Recovery in Carbonate Reservoirs

“…The adsorption layer is formed by orientation of carboxyl groups toward calcite surface because the surface carries positive charges. [23] For engineering purposes, the adsorption isotherms are also plotted as adsorption amount (mg of NA per g calcite powder) versus total acid number (TAN) and are shown in Figure 3. TANs were calculated by amount (in mg) of KOH required to neutralize NA in 1 mL of the oil.…”

“…The experimental body of this work is given in detail in a SPE paper (SPE 99612) that was presented at the SPE/DOE Symposium of Improved Oil Recovery at Tulsa, Oklahoma April [22][23][24]2006. This paper has been submitted to SPE for peer review, and has been accepted for publication pending a review of the revisions recently provided by the authors.…”

“…[16] It is generally accepted that adsorption of polar compounds onto rock surface has a significant effect on the wettability of reservoirs. [17][18][19][20][21][22][23][24] In other words, the wettability of hydrocarbon reservoirs depends on the specific interactions in the oil/rock/brine systems. Naphthenic acids are the products of extensive oxidation of crude oil and play an important role in wettability control of reservoirs.…”

Effect of Brine Composition on Wettability Alteration of Carbonate Rocks in the Presence of Polar Compounds

“…Specifically the neutral to oil-wet character of carbonate reservoirs may be related to the adsorption of carboxylate molecules diffusing from crude oil to positive sites of the calcite surface [41]. In other words, the wettability of hydrocarbon reservoirs depends on the specific interactions in the oil/rock/brine systems.…”

“…Hansen [9] suggested that strong adsorption of stearic acid on the calcite surface converts the calcite surface to strongly oil-wet. Legens [41] investigated the adsorption difference of benzoic and lauric acids on calcite surface from toluene and water.…”