Abstract
Long-term thermal stability of surfactants under harsh reservoir conditions is one of the main challenges for surfactant injection. Most of the commercially available surfactants thermally degrade or precipitate when exposed to high-temperature and high-salinity conditions. In this work, we designed and synthesized three novel betaine-based polyoxyethylene zwitterionic surfactants containing different head groups (carboxybetaine, sulfobetaine, and hydroxysulfobetaine) and bearing an unsaturated tail. The impact of the surfactant head group on the long-term thermal stability, foam stability, and surfactant–polymer interactions were examined. The thermal stability of the surfactants was assessed by monitoring the structural changes when exposed at high temperature (90 °C) for three months using 1H-NMR, 13C-NMR, and FTIR analysis. All surfactants were found thermally stable regardless of the headgroup and no structural changes were evidenced. The surfactant–polymer interactions were dominant in deionized water. However, in seawater, the surfactant addition had no effect on the rheological properties. Similarly, changing the headgroup of polyoxyethylene zwitterionic surfactants had no major effect on the foamability and foam stability. The findings of the present study reveal that the betaine-based polyoxyethylene zwitterionic surfactant can be a good choice for enhanced oil recovery application and the nature of the headgroup has no major impact on the thermal, rheological, and foaming properties of the surfactant in typical harsh reservoir conditions (high salinity, high temperature).
Highlights
Surfactants consist of head groups and tail groups and are mainly used to change the surface properties at the gas–liquid, liquid–liquid, and solid–liquid interface
The findings of the present study reveal that the betaine-based polyoxyethylene zwitterionic surfactant can be a good choice for enhanced oil recovery application and the nature of the headgroup has no major impact on the thermal, rheological, and foaming properties of the surfactant in typical harsh reservoir conditions
The material used for the preparation of oleyl polyoxyethylene amidopropyl hydroxy sulfobetaine (OPAH), oleyl polyoxyethylene amidopropyl sulfobetaine (OPAS), and oleyl polyoxyethylene amidopropyl carboxybetaine (OPAC) was depicted in our preceding article [33]
Summary
Surfactants consist of head groups (hydrophilic) and tail groups (hydrophobic) and are mainly used to change the surface properties at the gas–liquid (surface tension), liquid–liquid (interfacial tension), and solid–liquid (wettability) interface. The foaming properties of surfactants are important for oilfield applications, such as in gas injection-based EOR processes. The channeling, which is a typical issue in heterogeneous reservoirs, can be minimized by foam as it is more stable in high permeability zones This stability in high permeability zones increases the flow resistance and diverts the gas to low permeability zones. The impact of different headgroups on the thermal stability, surfactant–polymer interactions, and foaming properties of three newly synthesized betaine-based polyoxyethylene surfactants, namely oleyl polyoxyethylene amidopropyl hydroxy sulfobetaine (OPAH), oleyl polyoxyethylene amidopropyl sulfobetaine (OPAS), and oleyl polyoxyethylene amidopropyl carboxybetaine (OPAC), were investigated. The synthesis and surface properties of these surfactants were already reported in our previous publication [33]
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