Effect of Electrolytes on Solution and Interfacial Behaviors of Double Chain Cationic-Nonionic Surfactant Mixtures for Hydrophobic Surface Wetting and Oil/Water Emulsion Stability Applications

The solution behaviors of the binary mixture of double chain cationic surfactant didodecyldimethylammonium bromide (DDAB) with nonionic surfactants of varied head groups, EO-9 and EO-40, in the presence and absence of electrolytes were studied and found nonideal behavior. The different physicochemical properties such as Gibb's surface excess (Γ), minimum area per molecule (A_min), and interaction parameters at bulk (β^M) and interface (β^σ) were calculated. In the presence of nonionic surfactants, lowering of CMC, CVC, and surface tension at these two concentrations of DDAB were observed. The β^M and β^σ values indicate strong interaction between DDAB and EO-40 mixed system. Further, addition of electrolytes to the mixed systems show increased interaction and change of physicochemical properties because of the combination of electrical and salting out effects.

Performance Evaluation and Application of the Surfactant Combinations showing Ultra-low Oil-Water Interfacial Tensions

In order to select a surfactant formulation with an ultra-low oil-water interfacial tension for application in a low permeability oil field, surfactant combinations were developed consisting of non-ionic alkanolamides, anionic alkyl benzene sulfonate and betaine in certain proportions. The results showed that the oil-water interfacial tension (oil from the Changing Jing'an field) could decease to 10−4 mN m−1∼10−5 mN m−1 in the wide surfactant concentration range of 0.3%∼0.6% and a salinity of 100 000 mg L−1 at 40°C∼70°C. From 2012 to 2013, the field tests of 8 injection and 39 production wells were carried out. The water-cut escalating rate decreased from + 1.26% to −0.15% monthly. The yield changing rate increased from −1.59% monthly to + 0.12%. The valid period of the test was more than 10 months. The improved oil recovery of the in-test well groups were predicted to increase 6.3% using type A characteristic curve of drive water. When comparing the three injection technologies, the key to the success of field application of surfactant combinations having an ultra-low oil-to-water interfacial tension is a consistent profile protocol of water injection.