Interfacial Shear Rheology of Gels Formed at the Oil/Water Interface by Tetrameric Acid and Calcium Ion: Influence of Tetrameric Acid Structure and Oil Composition

Abstract

The tetrameric acid ARN is present in crude oil and can form deposits that can cause plugging in oil production facilities during oil production in the presence of calcium ions. It has been previously shown that BP-10, a compound designed to mimic the properties of ARN, can form gel at the oil/water interface by reacting with Ca 2+ if the pH is high enough to ionize BP10s carboxylic acid functions. In this study, the BP-10 and ARN are compared. Although BP-10 forms a gel at the interface, ARN creates rather a viscoelastic material perhaps due to the presence of impurities like naphthenic acids in the sample analyzed. The amount of BP-10 required to form a gel at the interface was found to be ca. 0.45−0.76 mg·m −2 . The influence of the presence of asphaltenes on the gel formation has then been studied. It has been found that the gel is weakened in the presence of asphaltenes and G′ is not measurable at high enough concentrations. This inhibition could result from either a competition between ARN and asphaltenes to adsorb at interface or complexation of ARN and asphaltenes in the oil bulk phase. The influence of naphthenic acid (NA) on the gel formation was also studied by considering a commercial mixture of NA from Fluka. It is shown that NA can inhibit the gel formation of ARN or BP-10 at the oil/water interface most likely by acting as a cross-linking termination point agent. Finally, the effect of commercial calcium naphthenate inhibitors on gel strength has been studied. It is found that the inhibitors delay the formation of tetrameric acid gels and reduce their elastic modulus G′. However, results show that the order of inhibitor efficiency depends on the tetrameric acid used (ARN or BP-10). This could be linked to different specific inhibitor/TA interactions between ARN and BP-10. In conclusion, interfacial shear rheology appears to be a promising method to screen calcium naphthenate inhibitor.

Rheological Properties of Gels Formed at the Oil–Water Interface by the Reaction between Tetrameric Acid and Calcium Ion under Flow Conditions and at the Batch Scale

“…ARN is very surface active and adsorbs at the oil-water interface, especially when ionized 11,24 . In this state, ARN can form a gel at the oil-water interface by reaction with calcium [25][26][27][28] . It is thought that this gel forming properties is due to the presence of 4 carboxylate groups per molecule acting as reticulation point after reaction with Ca 2+ similarly to polymeric gels.…”

Flow instabilities due to the interfacial formation of surfactant–fatty acid material in a Hele-Shaw cell

“…Given the original connection between the work of Saffman & Taylor and oil recovery in porous media [1], it is interesting that our results may have relevance to aspects of crude oil processing, such as the formation of gellike structures when a crude oil component (tetrameric acid) with a carboxylic head group reacts with calcium ions at a water surface [24,48]. We expect that further study of the dynamics of this surfactant/fatty acid material and its formation at fluid interfaces may also have implications for related phenomena in drug delivery [49] and the production of artificial cells [42,50,51].…”

“…Although oil and water are immiscible, certain oils are comprised of molecules which interact with aqueous solutions at an interface. For instance, precipitation and gel formation reactions are known to occur between crude oil (and its derivatives) and water [24][25][26]. Interfacial gellike material has been observed in immiscible systems of aqueous cationic surfactants and oil-based fatty acids [20,27,28].…”

“…The molecular organization comes from the fact that ionized fatty acids can associate with the surfactant head cation by electrostatic interactions, similar to what exists in catanionic surfactant systems [41,44,45], while neutral and ionized fatty acids interact via hydrogen bonding [40]. There are many studies on different fatty acid/cationic systems [20,24,43], other types of carboxylic acid/cationic system (including CPCl) [46,47], as well as pure catanionic surfactant systems [44,45]. We expect that the selfassembly of CPCl/oleic acid shares similarities with these systems, although to the best of our knowledge the microstructure, intermolecular interactions, and resultant physical properties have thus far not been studied.…”

Rapid Stabilization of Immiscible Fluids using Nanostructured Interfaces via Surfactant Association

“…However, research on dynamic phenomena in which structural self-assembly stabilizes the interface under nonequilibrium conditions is still in its infancy. This is despite the fact that in situ self-association of amphiphilic molecules has been widely observed for a variety of practical or industrial applications including oil recovery [45][46][47], flow instabilities [20,[48][49][50][51], biological systems [52][53][54], and rare metal extraction [55]. There has yet to be a fundamental study on dynamics of interfacial material formation between associating surfactants at immiscible liquid interfaces, and the connection between structure and property relationships, in addition to the underlying mechanism of structure development at the molecular level.…”