Microemulsion Flooding of Heavy Oil Using Biodiesel Under Cold Conditions

Abstract

Cost and thermal stability are the major obstacles in using chemical additives for enhanced heavy-oil applications. Visual analysis of biodiesel in water emulsions obtained from the bitumen recovery tests from previous studies demonstrated that high pressure steam can lead to formation of stable emulsion by evaporation of biodiesel and condensation of steam-biodiesel vapor in the reservoir. Hence, biodiesel can be an alternative to commercial surfactants as a low-cost and environmentally-friendly additive for hot and cold production of heavy-oil. For biodiesel to act as a surfactant and reduce IFT, it must first be condensated. Hence, we first studied the thermal-mechanical processing of biodiesel to generate stable steam treated homogenized biodiesel-in-water emulsion (SBDWE). Addition of chemicals such as silica and polymer (Xanthan gum) to further improve the stability of SBDWE was also considered in this study. Stable SBDWE samples generated at their optimal conditions were then employed for sandpack flooding experiments to observe their capacity to improve heavy oil recovery. In order to create stable SBDWE, biodiesel was first treated with steam at high pressure and high temperature conditions (1.6 MPa, 200°C). Variables such as reactor pressure, concentration of biodiesel in steam, and condensation time were modified independently to determine the optimal conditions for stable SBDWE generation. Surfactant behavior of the SBDWE samples was then tested through various methods (glass tube experiments, spreading tests through transmitted-light microscope, and naked eye visualization) The results from the experiments suggest that aggregation of the small-sized biodiesel droplets of SBDWE (~1μm) at the interface between heavy oil and SBDWE can form a stable emulsion phase. Creaming of SBDWE is a poor emulsification indication and can be avoided by controlling experimental variables such as injected volume of distillate water, concentration of injected biodiesel, soaking time, and addition of silica nanofluid. Storage of the stable SBDWE is also an important factor as SBDWE properties such as texture, color and stability can change over time. Injected water volume (representing steam) and soaking time are variables that can have a significant impact on the generation of stable SBDWE. Therefore, it is important to maintain a certain volume of water and soaking time during the homogenization treatment. Finally, displacement experiments on sandpacks with the help of low concentration of silica (1 wt. %) and Xanthan gum (0.35 wt.%) yielded additional recovery up to ~39%. Environmentally friendly and relatively inexpensive biodiesel (as a by-product of many industrial applications) is an ideal candidate for enhanced heavy oil recovery. Previously, application of biodiesel in heavy oil recovery came with limitations such that in enhanced heavy oil recovery, it is most effective when added to steam at high temperature and pressure conditions. However, the results from the laboratory scale cold flooding experiments with SBDWE demonstrated that SBDWE can be effectively used as a chemical additive using low concentrations of biodiesel.