Abstract
Surfactant flooding is an important enhanced oil recovery (EOR) method, especially in carbonate oil reservoirs where water flooding may not have an effect on oil recovery as much as for sandstone reservoirs. This is because of the initial wettability of most carbonate reservoirs that is mixed- or oil-wet. Since surfactant flooding has a great impact on both fluid–fluid and rock–fluid interactions, it can be an efficient EOR method for these kinds of reservoirs. Surfactants affect fluid–fluid interactions by reducing interfacial tension (IFT) between water and oil phases and rock–fluid interactions by wettability alteration. The objective of this paper is the evaluation of these two surfactant mechanisms in non-fractured carbonate reservoirs using UTCHEM, the University of Texas chemical compositional simulator. In this paper, first, the laboratory data of two surfactant spontaneous imbibition tests for carbonate cores are successfully matched with modeled data to evaluate the mechanisms of surfactant flooding. Second, the field-scale surfactant flooding is simulated using the experimental data from spontaneous imbibition tests. Several cases are modeled in order to study the effect of surfactant flooding in terms of decreasing IFT and wettability alteration. Since the formation brine salinity in most reservoirs is more than the optimum salinity of surfactant phase behavior, the benefit of combining surfactant and low-salinity water is also investigated. Finally, tracer test simulation is performed to estimate the average oil saturation within the swept pore volume at the end of each recovery mode.
Highlights
It is widely accepted that in petroleum reservoirs only a small fraction of the original oil-in-place is economically recoverable by primary recovery methods via natural forces and secondary recovery via waterflooding
It can be concluded that the combination of surfactant flooding and low-salinity water at optimum salinity level of the surfactant phase behavior can have the highest efficiency on cumulative oil recovery
It has been suggested that while the effect of lowsalinity water as a single enhanced oil recovery (EOR) method is very dependent on the initial wetting condition, the combination with surfactant has a significant effect on surfactant phase behavior to reach ultra-low interfacial tension (IFT) in high-salinity reservoirs
Summary
It is widely accepted that in petroleum reservoirs only a small fraction of the original oil-in-place is economically recoverable by primary recovery methods via natural forces and secondary recovery via waterflooding. A significant amount of oil ends up unrecovered in porous media which results in an oil recovery factor typically less than 50% (Teklu et al 2013). Since the main mechanisms of all EOR methods are directly related to fluid–fluid and fluid–rock interactions, the effects of these two concepts in Sor reduction are investigated as follows: Fluid–fluid interactions This type of interactions in porous media is governed by the interplay between capillary, viscous and gravitational forces. A number of different mathematical relations between NB and NC have been proposed by various researchers (Cense and Berg 2009) These two dimensionless numbers were combined by Jin (1995) into a total trapping number (NT) to examine residual mobilization in an arbitrary flow regime having both horizontal and vertical components of flow. NT can be increased in three ways: 1. Increasing the injection fluid velocity: The injection fluid velocity is limited by pump capacity and the formation injectivity
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