Zengbao Wang

Low Interfacial Tension Behavior Between Organic Alkali/Surfactant/Polymer System and Crude Oil

Oil recovery has a great relationship with the interfacial tension (IFT) between displacing fluid and crude oil when using alkali/surfactant/polymer (ASP) aqueous solution to displace oil in reservoir. Alkali such as sodium hydroxide and sodium carbonate are often used to enhance the applied performances of surfactant and polymer. In this paper, two kinds of organic alkalis, triethylamine (TEA) and monoethanolamine (MEA), are applied together with Shengli petroleum sulfonate (SLPS) and partially hydrolyzed polyacrylamide (HPAM) to form two novel organic alkali/surfactant/ polymer (OASP) systems. The dynamic IFT is measured by using the spinning drop IFT meter. The optimum applied concentrations of SLPS, TEA, MEA, and three kinds of HPAM are selected by referring to the dynamic IFT between their aqueous solutions and oil. TEA and MEA both have synergistic effect and can reduce IFT to 10−3mN/m or lower when they are used with SLPS. The formulae of two novel low IFT OASP systems are obtained. These two OASP systems can reduce IFT to the value lower than 10−2mN/m when they are prepared using the produced water. Some influencing factors such as salinity, temperature and shearing are tested by measuring the minimum IFT of OASP aqueous solutions and oil. The results show that two OASP systems both have good tolerance toward these factors. Core displacing experiment is also conducted and the results approve that two OASP systems both can enhance the oil recovery efficiently.

Study of a Double Cross-Linked HPAM Gel for in-Depth Profile Control

The concept of profile control is one of the most important strategies to enhance oil recovery in a high water production field, with polymer gels being used as a gelant matrix in various reservoirs around the globe. In an effort to reach a suitable profile control, previous attempts lead to an increase of polymer concentration, resulting in a poor injection and insufficient in-depth profile control. The work presented here introduces a novel gel system, using both key functional groups on HPAM to react with two types of cross-linking agents. Different formulations and the properties of this double cross-linked HPAM gel system have been studied. The experimental results indicate that the studied double cross-linked HPAM gel system exhibits a higher gel strength, an improved salt and shear resistance as well as an improved plugging effect compared to a single cross-linked HPAM gel system. Moreover, as a result of higher gel strength, the double cross-linked HPAM gel system also shows a longer gelation time, a parameter particularly useful for in-depth profile control. The gel microstructures have been evaluated, with the double cross-linked HPAM gel exhibiting a molecular structure that is more compact. The latter is a clear indication for the improved properties of the system as will be detailed in subsequent sections. GRAPHICAL ABSTRACT

Effect of Molecular Structure on Interfacial Activity and Emulsification Property

Abstract This paper presents the reasons for the differences in interface tension and emulsion stability of Span60, Tween20, Tween60, Tween80 from the perspective of the molecular structure. For a surfactant emulsion, there is no complete correlation between interfacial tension and emulsion stability. Interface tension cannot determine the emulsion stability, but the molecular structure of the surfactant is the determinant of both the interface tension and emulsion stability. The branching degree of hydrophilic group, carbon chain length of hydrophobic group and carbon-carbon double bond had played a very important role. The clarification of the effect of molecular structure has significant theoretical meanings for modifying and synthetizing new surfactants.

Research on the Emulsifying Ability of Surfactants in Crude Oil

Abstract A novel colorimetric method to measure the emulsifying ability of surfactants for crude oil has been proposed. The emulsifying ability of five surfactants for two kinds of crude oil was determined at different temperatures and salinities. The oil-water interfacial tension, particle size distribution of emulsion, emulsion stability and ability of reducing viscosity by emulsifying were investigated at the corresponding condition. The results show that there is no correlation between emulsifying ability and HLB value of surfactants. The property of crude oil has a certain impact on the emulsifying ability, and the interfacial activity is the main influencing factor on it. The emulsifying ability is affected obviously by temperature. At first it increases and then it decreases with rising temperature. Inorganic salts of low concentration are beneficial to enhance the emulsifying ability. The emulsifying ability has negative correlation with the particle size of emulsion, and positive correlation with the ability of reducing viscosity by emulsifying. There is no inevitable relation between emulsifying ability and emulsion stability.