Abstract
For heavy oil reservoirs (with oil viscosities ranging from 1,000 to more than 10,000 mPa-s), primary production and waterflood can only recover 5 to 10% initial oil-in-place (IOIP) due to the unfavourable mobility ratio of the water phase to the oil phase. Heavy oils usually have a relatively high content of organic acids, which can be neutralized by alkalis to form in-situ surfactants. With the assistance of these in-situ surfactants, an oil-in-water emulsion with a much lower viscosity than heavy oil can be generated. In this way, the heavy oil is entrained in the water phase and produced out of the reservoir.
An initial study was carried out to evaluate the feasibility of alkaline/surfactant (A/S) flooding for western Canadian heavy oil reservoirs. The integrated approach included extensive emulsification tests, oil/brine interfacial tension measurements, viscosity measurements, and sandpack flood tests. The experimental results showed that the dynamic interfacial tension of oil/water can be lowered to an ultralow level (< 0.01 dyne/cm) by an alkaline solution and a very dilute concentration of surfactant, leading to easy emulsification of heavy oil in formation brine under slight interfacial disturbance. A series of sandpack flood tests were carried out to investigate the recovery performance of A/S flooding for five western Canadian heavy oils with viscosities ranging from 650 to 18,000 mPa-s at 22°C. Tertiary oil recoveries in sandpack flood tests were between 20 to 30% IOIP. The results of these sandpack flood tests suggest that A/S flooding is a promising enhanced oil recovery process for thin heavy oil reservoirs, in which thermal processes are not suitable.
