Studies on the qualitative change of oil and flow properties of emulsion formed in in-situ combustion

Abstract

Our combustion tube experiments for in-situ combustion with many crude oils of various densities showed that produced oil became light and was emulsified in many cases. In theprevious paper, formation mechanism of emulsion was discussed.
In field operations, emulsification may cause serious problems. Then, at the present study, it was aimed to clarify the influence of emulsification to the flow properties of oil phase. Experiments were carried out with three crude oils made by distillation of Yabase crude oil which was easily emulsified. One was the original Yabase crude oil, and other two oils were the heavier and lighter oils that were made by eliminating the light component from Yabase crude oil and by adding the light component to Yabase crude oil, respectively. Results may be summarized as follows.
1) Dependency of the viscosity of emulsion on the density of oil and temperature is similar to that of crude oil, but emulsification emphasizes the dependency.
2) The water content of emulsion is the index of the degree of emulsification and most strongly influences the viscosity. The viscosity of the emulsion of highest water content of 75% increased by several ten to hundred times.
3) The W/O emulsion formed in the in-situ combustion has the pseudoplasticity and its viscosity becomes strongly dependent on the flow speed as the water content increases.
4) Though the increase of water content of emulsion eventuates in the low oil content, the residual emulsion saturation drastically increases with water content, so that the residual oil saturation does not vary so much. Therefore, the fuel necessary for successful in-situ combustion is held in the oil bed.