Abstract

By analyzing the continuous field tracking tests on the ASP combination flood crude oil emulsions, It was found that there are three types of crude oil emulsion by microscope equipment. They are water-in-oil emulsion (w/o type), oil-in-water emulsion (o/w type) and multiple emulsion (o/w/o type). Different emulsions are produced at different times, and fluids of different water ratios are being produced. A relatively easy emulsification between alkaline and crude oil is due to the formation of in-situ surface-active agents from the reaction of alkali and the materials in the crude oil. Low concentration of a surfactant, ORS-41 easily forms a w/o emulsion, but an o/w emulsion is formed in 0.3% wt ORS-41 solution.

The effect of de-emulsifiers on interfacial tensions, surface pressure and membrane strength concludes that the de-emulsifier enters into the interface and take the place of the adsorbed ORS-41 molecules or some other surface active materials at the interface. Experiments show that not only can the de-emulsifier lower the interfacial tensions of binary system (HPAM + NaOH), but it can also raise the interfacial tensions of the synthetic liquid system. The surface pressure results show that the de-emulsifier molecules replaced a portion of the surfactant. The de-emulsifier action mechanism is partial replacement of the interfacial active materials and lowering of the interfacial film strength.

Introduction

Alkaline/Surfactant/Polymer Flooding technique can increase oil recovery about 20% OOIP over water flooding both from lab experiment and pilot tests in Daqing Oilfield. A mixture of alkali, surfactant and polymer is used in the ASP combination flooding process for tertiary recovery of petroleum. Study of the emulsification and the de-emulsification mechanism is of theoretical as well as of practical value to fully understand the oil-displacement mechanism of ASP flooding and the de-emulsifying and de-watering of produced fluid. Due to the presence of natural emulsifiers, crude oil can easily form stable water-in-oil emulsion in the process of primary and secondary oil production. The stability of the crude oil emulsion is mainly determined by the oil-water interfacial film which is derived from natural emulsifiers1–4. Crude oil emulsion, under the influence of interfacial film and crude oil viscosity, is dynamically stable5. Articles summarizing the stability of crude oil emulsions have been published in China6,7. Much more research works have been carried out on the de-emulsification of ASP crude oil emulsions8–11, however, no reports has been seen about a general rule of ASP-crude oil emulsifying properties whether the ASP ternary components exist separately or in combination.

Great success has been achieved on the development of de-emulsifiers which are inorganic matter to organic matter, ionic type to nonionic type, small molecules, macro-molecules, and even massive materials of super polymers. In spite of this, our knowledge of the de-emulsification mechanism is still far from being completed. According to Taylor12, the major action of de-emulsifiers is to lower the viscosity of the interfacial film. Sjoblom et al.[3] showed how medium-length-chain alcohol destructively affects North Sea crude oil emulsions, which suggests that the more alcohol is addded, the greater the destructive action becomes. They concluded that in the process of emulsification, the inter-actions between the interfacial film of crude oil emulsion and the de-emulsifier added are of great importance. De-emulsifier AOT mixed with the interfacial film gives electric charges which can make closely accumulated molecular films change their characteristics thus leading to de-emulsification.

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