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Oil Rim Development |
Den norske stats oljeselskap a.s., Trondheim, Norway
This paper describes the basic mechanisms by which waterflood residual oil is mobilized and recovered during tertiary surfactant flooding in strongly water-wet glass micromodels. Of the two models used, one displayed a uniform and the other one a more heterogeneous distribution of water flood residual oil. Mobilization of residual oil proceeds by an imbibition-drainage mechanism where a surfactant imbibition displacement is always associated with a corresponding oil-water displacement (drainage) process. The drainage results in reconnection of residual oil and leads to the formation of an oil bank whilst the imbibition process may lead to breakup and trapping of mobilized oil. Although the magnitude of the residual oil saturation was similar for both models, microscopic sweep and recovery efficiency are found to be significantly higher when the residual oil is uniformly distributed. For more heterogeneous distributions of residual oil, surfactant flow through low resistance water paths results in substantial dispersion and early surfactant breakthrough.
