Microscopic study of emulsion flow in porous media

Abstract

Emulsion applicability as an oil recovery agent has long been recognized in petroleum industry. However, investigations of emulsion flow in porous media for petroleum recovery applications are scarce; particularly the flow effects have not been explained in detail in term of events occurring at the pore level. Thus, this research was carried out to investigate the physics of emulsion flow in porous media. The objectives of the experiments are to study the behavior and mechanism of emulsion flow in porous media, to evaluate the effectiveness of emulsion as an oil recovery agent, and to determine the emulsion blocking processes. In this research, well characterized emulsions of water-in-oil emulsion (model oil of 86.5% dibutylphthalate + 13.5% n-heptane, and distilled water system) and oil-in-water emulsion (paraffin oil, distilled water, and Triton-X100 surfactant system) were injected into two-dimensional etched glass micromodels. Visualization experiments by using microscope on the micromodels were conducted to observe and record the emulsion droplet motion, captured mechanisms, and blockage processes. The results demonstrate the three possible flow regimes that may occur when emulsion flow in porous media are mainly due to the difference of emulsion droplet size to pore throat ratios. Flow phenomena of emulsion droplet formation, deformation and destruction, blob and rivulet were observed to be associated with less stable emulsion system. Other emulsion flow phenomena were the microstructures of droplets adhesion and entrainment from the solid surface, and droplets undergone snap-off and division from pore-to-pore. The results show that the emulsion droplets were found to be captured at the throat and the pore body according to straining and interception capture mechanisms. Also, the results indicate that wettability has a direct influence on the droplet capture mechanism. Emulsion water droplet colliding with the waterwet surface could easily adhere to the surface and formed thick water films. On the other hand, emulsion water droplet contacting oil-wet surface could be displaced from the surface by the continuous oil phase. Moreover, the results reveal that continuous emulsion injections could provide additional oil recovery, but by injecting smaller size emulsion slugs prior to water injection would result in insignificant additional oil recovery. Microscopic mobility control was found to contribute to the oil recovery processes in homogeneous porous media, while macroscopic mobility control due to the emulsion blocking effect would contribute to the oil recovery processes in heterogeneous porous media. The emulsion blockage process was observed to be accelerated with large ratio of emulsion droplet-to-pore throat, coalescence of captured droplet, low emulsion flow rate, more viscous emulsion droplets, and emulsion droplet wetting the solid surface. In conclusion, this research characterizes the physics of emulsion flow in porous media and demonstrates its application as an effective oil recovery agent through emulsion blocking mechanisms. The novelty is the revelation of the process for emulsion droplet blockage effects in porous media.