Long Term Thermal Stability of Chemical EOR Surfactants

Abstract

Chemical enhanced oil recovery techniques progressively emerge as a means to increase mature oil fields production. In particular, surfactant flooding allows increasing oil production by lowering the interfacial tension between injection water and crude oil. The effectiveness of surfactants depends on their chemical stability over an extended period of time, which could be impaired by reservoir conditions in terms of temperature, salinity and oxidative conditions. Within the frame of this work, we monitored the chemical stability of several families of anionic surfactants in water, including alkyl ether sulfates, alkyl glyceryl ether sulfonates, alkyl benzene sulfonates and internal olefin sulfonates. Analytical methods were first developed to evaluate the chemical stability of these surfactants, including high pressure liquid chromatography (HPLC) and mixed-indicator titration techniques. The thermal stability of industrially representative surfactants was then monitored as a function of time at high temperature. Anionic surfactants designed to withstand high temperature conditions proved to be stable in oxygen controlled environments over a very long storage time. Alkyl benzene sulfonates, internal olefin sulfonates and alkyl glyceryl ether sulfonates (or alkyl alkoxyl glyceryl sulfonates) notably showed a very good stability over a year–long storage at 100°C. Alkyl ether sulfates (or alkyl alkoxy sulfates) showed by contrast a poor stability at 100°C as all the active contents were degraded in twenty four hours in deionized water and around four months in an alkaline buffer. The hydrolysis of the sulfate moiety at high temperature is probably responsible for the limited stability of alkyl ether sulfates at high temperature. This study highlights the strong benefit of using sulfonated anionic surfactants in EOR processes applied at high temperatures. In particular, it demonstrates the advantage of replacing alkyl ether sulfates by alkyl glyceryl ether sulfonates in order to insure the long term stability of a formulation developed to be injected during several years.

Adsorption Mechanisms of a Novel Cationic Gemini Surfactant onto Different Rocks

“…The HPLC analyses were performed on an Agilent 1290 Infinity II equipped with a 1260 Infinity II evaporative light scattering detector (ELSD). The ELSD is considered a universal sensor for a variety of surfactants. , The residual surfactant concentration of GS12 after the static adsorption experiments on rock powder was obtained from a calibration curve that correlates the ELSD peak area with known concentrations of GS12. By correlating the GS12 concentration with the initial concentration, it is possible to determine how much GS12 was adsorbed on the rock during the experiment.…”

Evaluation of modified cashew nutshell liquid as natural surfactants for chemical flooding in sandstone oil reservoirs

“…Furthermore, aside from the solubility and compatibility analysis, the thermal stability of the surfactant chemical over a long period of time at reservoir temperature is crucial in designing a stable yet effective natural surfactant for EOR process. Hocine et al [16] reported that in an oxygen free environment, sulfur-based anionic surfactants especially sulfonates remained chemically stable for a duration of 1 year at 100 ˚C temperature. Conversely, [20] in their evaluation of twenty-eight surfactants comprising of the four different types of surfactants, reported that only non-ionic and amphoteric surfactants showed good thermal stability at harsh reservoir conditions.…”

Long-Term Thermal Stability of Ionic Surfactants for Improving Oil Production at High-Salinity High-Temperature Conditions

“…In addition, Angstadt et al also highlighted the excellent stability of linear alkyl benzenesulfonate for temperatures up to 300 °C during steam injection in low-salinity conditions . Under high-salinity conditions, Hocine et al reported the degradation of sulfates and sulfonates up to 120 °C in months. , Regarding the thermal stability of types of surfactants, the concluding results showed that alkyl benzenesulfonate was superior to olefin sulfonate and petroleum sulfonate, which were more robust to temperature than sulfate surfactants. The degradation mechanism includes the loss of sulfonate or sulfate function by hydrolysis in an acidic or alkaline media, , along with oxidative attacks on the side alkyl chain when exposed to oxygen .…”