Enhanced oil recovery by flooding with aqueous surfactant solution : a model study and comparison with theory

• Main Author: Savory, Luke Daniel
• Other Authors: Fletcher, Paul D. I.
• Published: University of Hull 2015
• Subjects: 540; Chemistry
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.676696

The aim of the work within this thesis is to elucidate the details of enhanced oil recovery by surfactant solution flooding. This was achieved by determining the detailed surface chemistry and flow behaviour of model systems consisting of a packed column of calcium carbonate particles as the porous rock with interstices filled with a pure oil, and aqueous solutions of three different surfactants (an anionic, cationic and nonionic) as the displacing phase. Each three phase system is characterised in detail in terms of its surface chemistry properties, including; water-rock adsorption, water-oil interfacial tensions, water-oil-rock contact angles, aqueous phase behaviour, microemulsion phase behaviour and water-oil partitioning. Two models are derived to enable modelling of the oil recovery performance of the aqueous surfactant solutions being pumped through the powder packed columns with interstices filled with the oil. The first model enables the concentration of free surfactant, [surf]free, present within the packed columns during flooding to be calculated from the initial concentration pumped in, [surf]init. This allows a direct comparison between surface chemistry characterisation results (which relate to [surf]free) and %oil recovery results (which relate to [surf]init). The second two-part model shows how, based on the hypothesis that the residual oil is trapped in the form of liquid bridges between contacting calcite particles, the measured %oil recovery variation with surfactant concentration can be understood and predicted for concentrations of surfactant both below and above the cμc in terms of the characterisation results. It was found that, for surfactant concentrations < cμc, the oil recovery depends on the contact angle alone (when capillary forces are dominant over viscous forces, i.e. low capillary number regime). The predictions show that the oil recovery varies from 58 % with a 0 ° contact angle through the water to 82 % with a contact angle of 90 ° or greater. When surfactant concentration > cμc, additional oil is recovered by a solubilisation plus emulsification mechanism. Experimental results were in reasonable agreement with those predicted from the model.