The Interfacial Tension and Alkane Carbon Number (n_min) of Alkyl Benzene Sulfonates in Relation to Enhanced Oil Recovery. Part I: Effect of Surfactant Molecular Weight/Temperature and Electrolyte on n_min

Abstract

Twelve anionic monoisomeric surfactants based on the alkyl benzene sulfonic acid were prepared. In two sets of experiments, the (n_min) values were determined at 28 and 70°C for them. The n-hydrocarbon scans (n-C₅ to n-C₁₈) against the interfacial tension were used to determine the (n_min) values. The factors affecting (n_min) such as; molecular weight, branching of side chain, temperature and electrolyte addition were investigated. From the obtained results, it was found that the surfactants which has the highest molecular (8φ C₁₅ ABS) gave (n_min) equal 8, so it can be used in the enhanced oil recovery(EOR) without additives (the suitable (n_min) for EOR between 7-9). Otherwise, the lowest molecular weight surfactant (7φ C₁₃ ABS) gave (n_min) equal 5 without addition of alcohols or electrolyte. This case needs some additives to adjust the (n_min) in the range of 7 to 9. By investigation the factors affecting (n_min), it was found that the side chain of alkyl benzene shifted the (n_min) to the highest values. The increasing of temperature decreased the (n_min) values. Also, it was found that the (n_min) increased to high value by adding the electrolytes and alcohols. The mixture between surfactants with and without side chain shifted the (n_min) to the highest value. Using these parameters, the alkane carbon number (n_min) can be used to select the suitable solvent during the preparation of emulsion to get the minimum interfacial tension at which the maximum emulsion stability should be obtained and also to select the surfactant for EOR.

Keywords:

• Alkane carbon number
• alkyl benzene derivatives
• anionic surfactants
• emulsion stability
• enhanced oil recovery
• interfacial tension

Notes

*N.A: Out of liquid hydrocarbon scale (gaseous scale; not available to measure.

USB: Unsymmetrical branch.

SB: Symmetrical branch.

IFT: Interfacial tension at the n_min.

•: Surfactant concentration is 0.07% by wt. and no alcohol.

*: Off liquid scale n-alkane and minimum tension.

Δ: At this electrolyte concentration and temperature, the surfactant precipitates.

^•%Electrolyte wt%: 0.1% CaCl₂, surfactant wt%: 0.07.

^•: Surfactant concentration is 0.07% by wt. and no alcohol.

^•: Electrolyte wt%: 0.1% CaCl₂, surfactant wt%: 0.07%.

Alcohol mixture is: 3.5% iso-pentanol, 2.0% t-buatnol, and 0.5% n-hexanol.

Electrolyte wt%: 0.1% CaCl₂.

*: Electrolyte wt%: 0.1% NaCl.

*: n_min is out of liquid scale hydrocarbon.