Effect of wax precipitation irreversibility on flowability and water flooding for high pour point crude oil in low permeability reservoir

Key words:  high pour point oil  temperature  wax precipitation irreversibility  flowability  water flooding recovery

Abstract:

Wax precipitation of high pour point oil is irreversible, which has significant effect on development of water injection and other enhanced methods. Under cooling and heating procedures, the wax precipitation-wax dissolution behavior, viscosity, rheological property, oil phase seepage ability and water flooding efficiency of high pour point oil were systematically compared. The results show that the wax dissolution temperature of a high pour point oil is 71.5°C, which is significantly higher than the wax precipitation point of 62.3 °C, and there is irreversibility. When the temperature is higher than the wax dissolution point, the crude oil viscosity values in the cooling and heating modes are basically the same, and the water flooding recoveries are equivalent. When the temperature of the crude oil is between the wax dissolution point and the wax precipitation point, the wax does not precipitate during the cooling process, and the viscosity is relatively small, showing Newtonian fluid performance and having no seepage starting pressure, and higher water flooding recovery (more than 60%). In the heating mode, the wax crystal is not completely dissolved, the viscosity is high, and it is a non-Newtonian fluid. There is a starting pressure, and water flooding recovery is significantly reduced ( less than 50% ), indicating the obvious irreversible effect. Considering cold damage of high pour point oil reservoir, its temperature is not enough to be slightly increased by hot water injection, and it should reach above the wax melting point, otherwise the water flooding efficiency will be significantly worse.