Chemical Interactions and Demulsifier Characteristics for Enhanced Oil Recovery Applications

Abstract

In this study, a design of experiments was used to investigate the importance of several parameters (alkaline concentration, anionic surfactant concentration, polymer concentration, temperature, shear rate, water cut, and salinity) and their interactions (i.e., synergism or antagonism) that govern emulsion stability in chemical enhanced oil recovery (CEOR). Emulsion stability decreased with an increase in salinity or water cut. An increasing surfactant concentration, polymer concentration, temperature, or shear rate enhanced emulsion stability. One of the main contributions for the tight emulsion from alkaline surfactant polymer (ASP) flood was the addition of alkaline. The surfactant, alkaline, and polymer decreased the size of oil droplets, increased the surface charge of oil droplets, and increased the film elasticity, thereby making oil–water separation difficult. Selected cationic surfactants (patents pending) proved much more effective than conventional non-ionic resins and polymeric cationic flocculants in separating oil-in-water emulsions. The chemistry was also investigated by studying the effect of alkyl chain length (C8–C18) of benzyl and methyl quaternary compounds (quats) on demulsifying efficiency. As the surfactant concentration in the brine decreased, the concentration of the cationic demulsifier required to separate the emulsion decreased and the optimum chain length of the cationic demulsifier also changed. The particle video microscope and focused beam reflectance measurement probes showed a significant increase of the size of oil droplets and reduction in the number of oil droplets in the presence of a cationic surfactant. This is in agreement of a decrease of the anionic charge on the surface of the oil droplets and a reduction of the film elasticity in the cationic system. Measurements of interfacial properties, such as the interfacial tension reduction rate, interfacial tension, elastic modulus, and ζ potential, at the oil/brine solution interface were also conducted. A qualitative correlation was found between the interfacial tension reduction rate, elastic modulus, ζ potential, and phase separation. The interfacial tension reduction rate decreased, ζ potential became less negative, elastic modulus decreased, and the size of oil droplets remarkably increased when a cationic demulsifier or an amphoteric demulsifier (patents pending) was added to the emulsion. However, there appears to be no direct correlation with interfacial tension. Without direct information, this preliminary correlation may provide guidelines for selecting demulsifiers for emulsions produced by chemical enhanced oil recovery.

Demulsification techniques of water-in-oil and oil-in-water emulsions in petroleum industry

“…On the other hand, positive or negative value of HLD corresponds to W/O or O/W emulsion, respectively, provided that the water-to-oil volumetric ratio (WOR) is almost close to unity [45]. At high WORs EOR where HLD is negative, a demulsifier must be added to ensure the combination of anionic surfactant and demulsifier leads to HLD = 0 or close to zero, associated with the least emulsion stability [55]. By qualitative employment of the HLD concept, Nguyen et al [55] used some cationic demulsifiers and realized that they accelerated the breakup of synthetic O/W emulsions emulsified by anionic surfactants, and attained oil and water phases with enhanced quality compared with the primary (untreated) emulsion.…”

“…At high WORs EOR where HLD is negative, a demulsifier must be added to ensure the combination of anionic surfactant and demulsifier leads to HLD = 0 or close to zero, associated with the least emulsion stability [55]. By qualitative employment of the HLD concept, Nguyen et al [55] used some cationic demulsifiers and realized that they accelerated the breakup of synthetic O/W emulsions emulsified by anionic surfactants, and attained oil and water phases with enhanced quality compared with the primary (untreated) emulsion. The concentration of demulsifier when mixed with anionic surfactants must generate HLD = 0, which is consistent with the evidence that a small variation in demulsifier concentration (below or above optimum value) may switch the emulsion from being unstable to stable, or vice versa.…”

“…For example, it has been observed that raising the salinity (NaCl) of O/W emulsions reduces their IFT, and expands the range of optimum demulsifier concentration at which minimum emulsion stability is achieved, implying that HLD can be shifted from negative to almost zero by increasing the emulsion salinity, thereby enhancing the demulsification effectiveness [55,66,67]. On the contrary, adding up to the aqueous phase salinity of W/O emulsions is expected to render them more stable, owing to lessened affinity of native surfactants to dispersed water phase [68].…”

“…As a result, it is expected that the interfacial adsorption of anionic surfactant in an O/W emulsion is reduced upon elevation of temperature, contributing to lower emulsion stability [77]. Nevertheless, conflicting finding has been published for the increase of temperature in produced water from ASP flooding containing anionic surfactant, representing enhanced emulsion stability [55], which might have been due to the opposing impact of salinity in the relevant system, giving rise to the improved adsorption of anionic surfactant at the oil-water interface. As pointed out in Section 2.4., stability of ionic surfactant-stabilized emulsions is often controlled by salinity (rather than temperature).…”

Modification of a nicotinic acid functionalized water‐soluble acrylamide sulfonate copolymer for chemically enhanced oil recovery

“…[1][2][3][4][5] Chemical flooding, such as surfactant flooding, polymer flooding, and alkali flooding, is an efficient way to get enhanced oil recovery (EOR) according to various studies. 6,7 Because of its feasible and economical operation and its ability to efficiently reduce the mobility ratio, polymer flooding has shown significant adaptability to existing reservoir conditions.…”