Chemical EOR is a common process to increase recovery in oil reservoirs but these techniques are limited today in the case of high temperature and hard brines, mainly due to high adsorption issues and thermal stability of the chemicals. Specific formulations of surfactant and/or surfactant-polymer have to be designed and injection strategy has to be adapted for these challenging cases.

In this paper we first investigate the evolution of surfactant phase behavior in high temperatures and high hardness conditions and the way surfactant formulations can be adapted to these conditions. Specific chemicals are required to withstand challenging environment, specifically high temperatures. Adapted lab protocols are also required including essentially anaerobic conditions. We demonstrate how properly selected chemicals can be successfully blended and adapted injection strategies designed in these conditions.

We then present at the lab scale the effect of temperature and brine composition on surfactant adsorption through oil recovery coreflood experiments. In addition, we show the way adsorption is reduced in the case of hard brines, by the use of a salinity gradient. In these cases, the optimization of the injection strategy can help reduce the surfactant loss. High oil recoveries together with moderate surfactant adsorption can then be achieved opening new opportunities for development of chemical EOR.

1. Background information

Surfactant-Polymer (SP) and Alkaline-Surfactant-Polymer (ASP) have been acknowledged for decades to be among the most promising techniques to enhance oil production and reserves in mature oil fields. These processes consist in the injection into a formation of chemical slugs composed of surfactants, polymer and in some cases alkali [1; 2].

Surfactants are used to decrease interfacial tension (IFT) leading to an additional mobilization of oil initially trapped by capillary forces in the rock matrix [1]. Polymers are used in order to improve mobility control and sweeping efficiency [1; 2]. The addition of alkali leads to a decrease of surfactant adsorption onto reservoir rock, specifically in presence of clays. Additionally, for reactive oils, alkali leads to the in-situ generation of soaps induced by the saponification of acidic crude oil components [3] improving overall process performances.

Most published successful studies so far focus on relatively favourable reservoir conditions. Under more challenging conditions, performance of ASP/SP flooding can drastically decrease [4]. Among specific hurdles, high salinity/hardness and/or high temperature make ASP/SP processes challenging, both at laboratory and field scale.

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