New Scaling Criteria For Chemical Flooding Experiments

Abstract This paper presents a set of scaling criteria for alkaline/polymer/cosurfactant flooding experiments. Numerous studies dealing with such chemical flooding experiments have been reported. However, these have been performed in unsealed models. This is due to lack of scaling criteria for the aforesaid processes. A new mathematical formulation has provided a complete representation of cosurfactant-enhanced alkaline/polymer processes. Unlike previous approaches, the proposed model accounts for transient interfacial tension (IFT) and non-equilibrium mass transfer phenomena. Laboratory experiments have suggested that of ultralow IFT values oil recm1eries become sensitive to transient IFT values. The presence of polymer modifies slightly the nature of dynamic IFT behaviour. The proposed model also incorporates alkali, polymer and surfactant adsorption, Also, chemical reactions and convective mass transfer along with diffusion and dispersion are accounted for. The governing partial differential equations are used to derive a new set of scaling criteria, also derived using dimensional analysis. This was particularly useful for processes for which a differential or parametric equation was not available. A variety of scaling options is investigated and their relative merits pointed out. Situations are considered, where by relaxing the requirement of geometric similarity the same fluid and same porous medium can be used. It is shown that for most situations the mass transfer rates have to be different in the model and the prototype. This finding contradicts the commonly used practice in laboratory experiments for which the mass transfer rate is assumed to be the same as in the field. The conditions for properly scaling adsorption, dynamic interfacial tension, mass transfer and all pressure-dependent properties along with dispersion are pointed out. The criteria for selecting the scaling group that if best suited for specific applications are recommended. Introduction Alkaline Flooding Alkaline flooding involves the injection of chemicals which react with acidic compounds in the crude oil to improve, the oil recovery by one or more of the following mechanisms:interfacial tension reduction(l-3)emulsification of oil(4)wettability aUeration5–6 Mayer et al. (7) described major chemical reactions occurring in an alkaline flood process, When alkali comes in contact with an acidic crude, the indigenous acids migrate to the oil/water interface and react with the alkali to produce organic salts which are mostly water soluble and surface active(8–9). This leads to reduced interfacial tension (IFT) to a level that permits the mobilizaton of residual oil globules (10–11). The surface active species are anions of dissociating electrolytes soluble in either phase(12). Also, alkali/water reactions serve to reduce the activity of multivalent cations present in the reservoir brines by forming precipitates, which can lead to improved oil recovery by blocking the more permeable channels. Rock/alkali reactions are considered to be detrimental to alkaline flooding because they are the main cause of alkali consumption. Rock minerals react with and deplete hydroxide ions from the injected alkaline solutions. Also, new minerals can precipitate. This might lead to permeability change and scale formation(15), Also, alkali/rock reactions can lead to altered wettability of the medium.