Emulsion-assisted thermal recovery method in heterogeneous oilsands reservoir

Abstract

To prevent the steam from channeling and breakthrough in heterogeneous oil sands reservoirs, oil-in-water (O/W) emulsion is proposed and developed as a plugging agent in this study. However, one suspects that increased temperature destabilizes emulsion, promoting oil/water separation and thus to lose its plugging benefits induced by “Jamin effect”. This intuitive picture changes when the emulsion flows through heated porous media. In this paper, we show that increasing temperature enhances emulsion plugging effect, after a critical temperature reaches. O/W emulsions were firstly prepared at room temperature (~20 °C) individually using eight different surfactants and then injected in sandpacks at temperatures ranging from 20 °C to 140 °C. Experimental results show that the emulsion plugging strength at temperature of 140 °C is three times greater than that at room temperature (20 °C) and still shows a rising trend with temperature up to 140 °C. Measurements of the median droplet sizes of the effluents at different temperatures showed that there was no phase separation during the flow tests. This is because that the “snap-off” and “fingering induced break-up” processes keep the emulsion droplets dynamically stable during the flowing process. It is the changing hydrophilic-lipophilic characteristic of the surfactant molecules, as the temperature increases, that causes a parabola trend with a minimum of IFT and thus influences the emulsion plugging effect. What we expect following steam injection into the reservoir is that the achieved emulsion plugging strength could still be maintained or even enhanced so that the emulsion slug will not be easily displaced away by further steam injection, thus optimizing thermal recovery performance. By carefully selecting surfactant on the basis of its hydrophilic-lipophilic characteristic, an optimum emulsion system, contributing expected plugging strength at elevated temperatures, was designed, applied and verified for effective conformance control in heterogeneous parallel-sandpack. The experimental results demonstrate the designed emulsion can achieve conformance control in parallel-sandpack with a permeability ratio of 10 Darcy: 5 Darcy at room temperature and the conformance performance is still maintained as the temperature increases, up to 99 °C.