Impact of Difficult Environments on Chemical Flooding Performance

Surfactant flooding processes become challenging when one of the following criteria is met: hard brines, high temperature, low permeability rock and high clay content. This paper illustrates how we overcome those difficulties combining appropriate formulations with the right injection strategy (slugs design). A particular emphasis is set on solutions that can be applied in the field. High performances solutions first rely on selecting appropriate surfactants from an extended portfolio representative of industrial products. We describe how ultra-low interfacial tension formulations are designed while maintaining a good solubility at high temperature (>100°C) and in hard brines (high divalent ion concentration). Various reservoir cases will then be reviewed:  In hard brines chemical adsorption is known to be significantly higher than in soft brines. Surfactant adsorption is drastically reduced (<0.2 mg/g) when using appropriate adsorption inhibitors. This results in a very high oil recovery (>90 %) with performances comparable to the one obtained in soft brine conditions.  High temperature (> 70-80°C) raises thermal stability issues with losses of effectiveness and possible plugging. New surfactants and polymers are available to address this situation. Successful oil recovery experiments done up to 120°C will be discussed.  Low permeability sandstone, usually associated with high clay levels has an impact on both injectivity and chemical adsorption. In most challenging conditions alkaline cannot be used and an optimized salinity gradient combined with adsorption inhibitors is requested. The paper will demonstrate how surfactant flooding can be successfully applied in challenging reservoir conditions to open new opportunities for chemical EOR.