Numerical and Experimental Investigation of Produced Water Reinjection on Viscous Oil Recovery

Abstract

Abstract Produced water treatment for superficial disposal is the main operational cost in heavy oilfields. Unfavorable mobility ratio and reservoir heterogeneities contribute to water fingering phenomenon that causes poor final recoveries. The use of diluted oil-in-water macroemulsions was evaluated as a mobility control method for these cases. An extensive experimental program was performed using silica sandpacks and sandstone plugs (Berea and Bentheimer) in order to evaluate final oil recovery factors, cumulative water-oil ratio and pressure behavior, comparing water injection, surfactant solution injection and oil-in-water emulsion injection. All porous media were saturated with crude oil from Campos Basin (22° API). A parametric study was performed to identify the effects of injection rate, oil droplets size distributions, emulsion oil concentration and permeability level in emulsion performance. Although the simulator used (CMG STARS®) does not have a specific model that describes the flow mechanisms related to emulsion injection, i.e., pore blockage dependence on size ratio between oil droplet/pore throat and local capillary number, a good match between predictions and experiments could be obtained by changing the oil-water permeability curves as a function of local emulsion concentration and by including an adsorption parameter to emulate oil droplet capture process. The results obtained have indicated final oil recovery improvement and cumulative water/oil reduction. It would be possible, after some treatment, to prepare diluted oil-in-water emulsions using produced water from the oilfield. That is the way to convert an effluent in a resource with clear environmental advantages. Introduction Oil and gas will keep their position as main sources of energy in the next decades. An important part of their future production will come from unconventional sources, like shale, tight formations and viscous oil reservoirs. The world energy consumption will to up 30% more in 2030 if compare to 2010 numbers [1]. To produce viscous oils in onshore oilfields there are some alternatives as steam flood, solvent injection and in situ combustion capable to achieve good oil recovery factors. Although, there are few economic recovery strategies for offshore viscous oilfields. Generally, water injection is the only economic viable alternative. Taking into account unfavorable mobility ratio and reservoir heterogeneities, the final oil recovery factors for these accumulations is, typically, less than 20%. A possible solution is the addition of a thickener to the water phase, such as polymer or any other additives to mitigate the unfavorable mobility issue. This does not mobilize residual oil phase. To change residual oil saturation it is necessary to lower interfacial tension using surfactants. This paper studies the use of dilute oil-in-water emulsions as option to enhance oil recovery factor in heavy oilfields. Nowadays, for each oil barrel produced, an average of 3 water barrels are produced in world scenario. This fact shows how important is to enhance, even slightly, water mobility control. Another important trend is that oil API degree is decreasing in world production. Indeed, excepting Brazilian Pre-Salt and Kashagan, all recent giant discoveries are viscous oil.