C an We Use Some Methods to Design Surfactants with Ultralow Oil/Water Interfacial Tension?

摘要

With recent advances in chemical combination flooding, the demand for high performance EOR surfactants is rapidly increasing. One of key parameters of the surfactants used in chemical combination flooding is the ability to decrease interfacial tension (IFT) between crude oil and displacing fluid to ultra-low level (10-3 mN/m). Most of time we use try and error method to screen surfactants, and now we begin to use molecule design theories to select reasonable surfactant molecular structure. Molecule design theories of surfactants, including Hydrophilic-Lipophilic Balance (HLB) value of surfactant, R-ratio (ratio of interaction energy of surfactant and oil with surfactant and water in interface layer), Molecule Geometry Packing Parameter (MGPP) and Quantitative Structure-Property Relationship (QSPR) were introduced and their application for oil displacement surfactants was discussed. HLB value equal around 6-9 can be used for primary designing and screening of oil-displacement surfactants, which is very convenient. By using HLB empirical equation, the hydrophobic group carbon chain of some of surfactants such as alkylbenzene sulfonate and alkyl naphthalene sulfonate can be optimized. R-ratio, MGPP, QSPR methods can be used in fine designing of oil-displacement surfactants. These methods consider more details of molecule interactions among surfactant, oil and water at interface layer. R-ratio method is still limited by the fact that some interaction energies cannot be measured experimentally. The packing parameter P of MGPP methods can be calculated base on Gibbs adsorption equation with model oil and water. The coincident ratio of MGPP methods for designing oil-displacement surfactants with ultra-low oil/water IFT is high based on 20 surfactants or surfactant mixtures. The correlation model between IFT and molecule structure parameters was established and the coincident ratio of QSPR methods for designing of oil-displacement surfactants with ultra-low IFT of hexadecane/water is good based on 39 surfactants. Based on molecule design theories, the structure characteristic of surfactants for chemical combination flooding should mainly focus on branch chains, double trails alkyl and/or aryl sulfonate surfactants, zwitterion surfactants, branching chain nonionic-anionic surfactants, gemini surfactants and so on.