Effect of Injection Water Quality on the Interfacial Tension of ASP/Crude Oil (2005)

Abstract ASP (alkali/surfactant/polymer) flooding has been successfully applied in several field pilots in Daqing oilfield in China. The oil recovery is improved by about 20% OOIP over recovery by water flooding. The interfacial tension (IFT) of ASP/crude oil is one of the most important factors that control the effectiveness of ASP flooding. The effects of alkali, surfactant, polymer and oil properties on IFT were previously studied. This paper addresses the effect of injection water quality on IFT of ASP/crude oil. This paper analyzes the inorganic ion compositions and organism compositions of injected waste water in different pilots in Daqing. The effect of these compositions and the suspension particles in injection water on IFT of ASP/oil were studied. A carboxylate surfactant was used in the study. All experiments were carried out at 45 ° C. Results showed that the suspension particles had little influence on IFT, inorganic ion compositions had some influence to some extent but were not the main factor affecting IFT for the low-salinity injection water used in ASP flooding in Daqing. The main factor increasing IFT is certain organisms in the injection water. The paper points out the main types of organisms influencing IFT. Some methods to lower IFT by controlling water quality are proposed. Introduction ASP (Alkali/Surfactant/Polymer) flooding technology was discovered in the early 1980s. Based on the cooperative effect of the three chemicals, ASP synergizes the three chemicals' functions and improves their efficiencies much more than singly. At the same time, it greatly reduces the amount of the chemicals needed, especially the expensive surfactant. With crude oil having a high acid number, ASP flood field tests obtained reasonably high recovery.(1, 2) The crude oil in Daqing is paraffin-based with a low acid number, &lt;0.1mg KOH/g. In the laboratory, Daqing oilfield obtained rather high recovery for a crude oil with such a low acid number. (3) Five ASP pilot tests were successfully performed in different well patterns, well spacings and reservoir conditions in Daqing oilfield. These pilot tests show that ASP flooding unequivocally enlarges the sweep volume, improves the displacement efficiency and produces incremental recovery of more than 20% OOIP than does water flooding.(4–6) There are many complex factors that can affect the efficiency of ASP flooding, such as the interfacial tension (IFT) of ASP/crude oil, adsorption loss of the ASP system in the formation, the viscosity and emulsification property of the ASP system, and the compatibility of the ASP system with the reservoir. IFT is one of the most important factors for screening out the appropriate ASP injection system. Measurement of IFT is the first step to determining the prescription for applying the ASP system. According to the capillary theory, under the conditions of the pressure gradient that can be reached through present technology, in order to activate the residual oil left by water flooding, IFT of ASP/crude oil should be decreased to 10- 3mN/m level. (7) Many factors can affect the IFT of ASP/crude oil: surfactant properties, crude oil compositions, the concentration and types of chemicals.