| dc.description.abstract | The present thesis addresses the effect of calcium ions on the interfacial chemistry between
oil and solutions of anionic surfactants, and its relevance for enhanced oil recovery (EOR)
methods at low salinity.
A number of scientific works have recently suggested a combination of low salinity water
(LSW) flooding and surfactant flooding as a promising new EOR approach. Surfactant
flooding has successfully been established in numerous fields worldwide, and relies on
reducing the capillary forces which trap crude oil within the porous reservoir rock. The EORpotential
of LSW-flooding, which, however, is still in its trial phase, is supposed to arise from
water-mineral interactions, promoting desorption of polar oil components from the rock
surface. An additional aim of combining both methods is to reduce retention and precipitation
of surfactant within the reservoir, which is of substantial importance for the economic
feasibility of the EOR-process.
The main focus of our study was the interfacial tension (IFT) between oil and water - one of
the basic values in surfactant flooding, and in EOR in general. While the surface activity of
ionic surfactants, as generally accepted, depends on the electrolyte concentration of its
solution, we chose the molar ratio between calcium and sodium ions as the key parameter.
The ionic strength was in most of the experiments kept constant, to evaluate the effect of the
calcium ions as precise as possible.
IFT measurements between surfactant solutions and oils - either crude oils, or chemically
inert hydrocarbons - were performed, both below and above the critical micellar
concentration. The respective results are summarized in the journal papers I - IV. In the
papers I and II, phenomenological insight in the effect of calcium on IFT is given, while
paper III presents a mechanistic approach of explanation; Latter is complemented by
molecular dynamics simulations. The interfacial activity of ionic surfactants was found to
increase systematically with increasing amounts of calcium in solution, analogous to the case
of increasing electrolyte concentrations. This effect seems to correlate directly with the
distribution of differently charged ions close to the interfacial adsorbed surfactant layer.
In paper IV, the empirical information obtained from the preceding papers is combined with a
first oil displacement study from oil saturated sandstone cores, in order to determine the
influence of calcium on the EOR-performance of an industrial surfactant formulation. Here,
oil recovery efficiency was strongly correlated to IFT changes caused by calcium ions.
Paper V and VI are dealing with desorption of polar oil components from silica surfaces upon
flushing with surfactant solutions of varying salinity. Here, a novel combination of Quartz
Crystal Microbalance and contact angle measurements, for measuring oil desorption and
surfactant adsorption quantitatively and to determine consequential wettability alterations of
the surfaces, was established. | nb_NO |
