Characterization of an alkyl diamine surfactant for gas mobility control in gas enhanced oil recovery and conformance control
The objective of this research is to characterize the properties and performance of an amine-based “switchable” surfactant, Duomeen TTM, at various environmental conditions. In particular, bulk characterization measurements namely, aqueous stability, solubility, partition, and rheological behavior were tested and applied in core flooding experiments using carbonate rock saturated in very saline brine. Aqueous stability provides insight about how Duomeen TTM solutions tolerate with changes in salt concentration, pH, and temperature. This surfactant becomes more hydrophilic as pH decreases and transforms into a viscoelastic solution at moderate to high salt concentrations. This viscoelasticity is intensified by changes in pH, temperature, and surfactant concentration of the solution, where surfactant concentration limits the aggregation density of the solution, pH influences the protonation process in the head group, and temperature controls the minimization of free energy by breaking, reformation, and branching of micellar networks. Furthermore, solubility measurements were conducted for a series of pressures and temperatures in pure CO2 as well as in gas mixtures composed of CO2 and CH4. It is shown that Duomeen TTM is very soluble in CO2, but becomes less soluble when methane is present in the system. Partition experiments amongst brine and CO2 reveal Duomeen TTM is very water soluble at low pH, in agreement with the aqueous stability results. Finally, these bulk characterization results were applied in core flooding experiments where in-situ viscoelasticity or gel development capabilities were tested with surfactant dissolved in solution at different salinities. In-situ viscosification is mainly dependent on the salinity contrast between the injective solution and resident brine as well as the rheological behavior of the surfactant solution at different salinities. This in-situ gel development provides mobility control by blocking thief zones and high permeable regions in porous media. In all, this ability to viscosify in-situ makes Duomeen TTM applicable for near-wellbore conformance control and CO2 mobility control in CO2 enhanced oil recovery.