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The Effect of Calcium Ions on Oil-Brine-Surfactant Interfacial Properties and the Relation to Surfactant Enhanced Oil Recovery at Low Salinity

Tichelkamp, Thomas
Doctoral thesis
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URI
http://hdl.handle.net/11250/2373581
Date
2015
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  • Institutt for kjemisk prosessteknologi [1214]
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.
Publisher
NTNU
Series
Doctoral thesis at NTNU;2015:228

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