Heavy Oil Recovery using ASP Flooding: A Pore-Level Experimental Study in Fractured Five-Spot Micromodels Mohammad Sedaghat, 1,§ Omid Mohammadzadeh, 2 * ,£ Shahin Kord 3 and Ioannis Chatzis 4 1. Department of Chemical and Petroleum Engineering, Sharif University of Technology, Tehran, Iran 2. Schlumberger DBR Technology Centre, Edmonton, AB, Canada 3. Ahvaz Faculty of Petroleum, Petroleum University of Technology, Ahvaz, Iran 4. Department of Petroleum Engineering, College of Engineering and Petroleum, Kuwait University, Kuwait Although alkaline-surfactant-polymer (ASP) flooding has proven efficient for heavy oil recovery, the displacement mechanisms and efficiency of this process should be discussed further in fractured porous media. In this study, several ASP flooding tests were conducted in fractured glass-etched micromodels with a typical waterflood geometrical configuration, i.e. five-spot injection-production pattern. The ASP flooding tests were conducted at constant injection flow rates but different fracture geometrical characteristics. The ASP solutions consisted of five polymers, two surfactants, and three alkaline types. It was found that using synthetic polymers, especially hydrolyzed polyacrylamide with high molecular mass, as well as cationic surfactant increases the ultimate recovery. The location of the injection well with respect to the fracture system plays a significant role in the ASP flooding performance, i.e. an increase in the angle associated with the longitudinal extension of fractures with respect to the main flow direction resulted in enhanced oil recovery and also postponed the wetting phase breakthrough time. Mechanistic study of this displacement process revealed that dispersive and diffusive behaviour of the ASP front enhanced the fluid transport from fracture to matrix and increased the microscopic displacement efficiency. Emulsification and coalescence mechanisms were responsible for ASP frontal advancement. Residual oil in the invaded region, which was observed in the form of discontinuous oil ganglia dispersed in the invaded pore bodies or in the form of pendular bridges formed around some of the solid particles, was mobilized in the form of oil wads through the droplets of the displacing phase. Keywords: ASP flooding, fracture, displacement mechanisms, heavy oil, micromodel INTRODUCTION C hemical flooding is of great interest because of the need to increase oil production, especially for reservoirs containing heavy oils. One of the most common chemical EOR processes is surfactant flooding, which significantly improves oil recovery because of the reduction in interfacial tension (IFT), evolution of micro-emulsions, and possible wettability changes of the formation even in dilute solutions. However, the ultimate sweep efficiency is not significant in dilute surfactant concen- trations. Sweep efficiency is defined as the ratio of oil volume displaced by the displacing agent to the initial volume of oil in place. Sweep efficiency is affected by mobility ratio, pore structure, reservoir rock wettability, reservoir heterogeneity, fractures, and properties of fractures. [5] The overall displacement efficiency can be enhanced by applying higher surfactant concentrations in which micelles form; however, this approach is not economical in most real field conditions. In order to overcome this issue, a relatively cheap co-surfactant and/or a viscosifier can be added to the dilute surfactant solution to make it economical from the operation point of view. In the alkaline flooding process, chemical reactions are formed between common alkali agents, such as sodium carbonate and sodium hydroxide, and organic acids in crude oil (i.e. saponifiable components) in order to generate in situ surfactants. The in situ formation of these soaps decreases the IFT between the displacing agent and the crude oil. Surfactants, whether synthetic or generated in situ as a result of chemical reaction of injected alkali with oil, reduce the IFT between the injecting phase and in situ oil. [13] Reduction in interfacial tension results in increased capillary number values associated with the flood, which reduces the residual oil value in the swept regions. [4,9] Using alkali as co-surfactants for chemical flooding can be an effective enhanced recovery process, especially for reservoirs containing heavy oil because of its higher acid content. In polymer flooding, the sweep efficiency is affected by the following: modification of the fractional flow, reduction of water-oil mobility ratio, and diversion of the injected water flow toward the un-swept zones. [12] Polymer flooding is not an effective method for mobilizing residual oil left behind in isolated pore spaces; it is mostly used as a conformance control technique (which stabilizes the flood front by viscosifying the injecting phase) and not as a remobilization process applicable to recovery of discontinuous isolated oil patched in the invaded region of the pore structure. There are some mechanisms responsible for displacement efficiency of visco-elastic polymer flooding such as pulling and stripping. [17] Since some residual oil remains bypassed in isolated dead end pores, a surface active agent (added directly to the injection stream or generated in situ, whichever is more practical and economical) is necessary to complement the polymer flooding in order to mobilize the § Now with Department of Petroleum Engineering, Montan University of Leoben, Austria £ Now with Schlumberger Doll Research, Cambridge, MA, USA * Author to whom correspondence may be addressed. E-mail address: omohamma@uwaterloo.ca Can. J. Chem. Eng. 94:779–791, 2016 © 2016 Canadian Society for Chemical Engineering DOI 10.1002/cjce.22445 Published online 1 March 2016 in Wiley Online Library (wileyonlinelibrary.com). VOLUME 94, APRIL 2016 THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING 779