Foamability and Foam Drainage of Sodium Naphthenate Solutions

Foams that arise during the extraction and processing of crude oil present a challenge in the petroleum industry, particularly in downstream processing during separation and refining, and effect oil recovery and gas production. The stability of crude oil foams are due to commercial surfactants used in enhanced oil recovery, and indigenous surface-active agents found within crude oil. Prominent among such surface species are naphthenic acids that react with salt found in water used during extraction, forming sodium naphthenates. With the depletion of light crude oil reserves and shift towards extracting heavier crude oils that have higher sodium naphthenate fraction, an understanding of how sodium naphthenates influence foam formation and stability is needed. The foamability of sodium naphthenate solution is correlated with its dynamic surface tension, that in turn depends on the mass transfer of surfactants to the fresh interface. As the dynamic adsorption of sodium naphthenate occurs relatively quickly (timescale < 50 ms), we utilize the maximum bubble pressure technique for it allows the necessary time resolution. The dynamic adsorption and dynamic surface tension measurements have not been reported before for aqueous sodium naphthenate solutions. Sodium naphthenates self-aggregate into micelles above a certain concentration called critical micelle concentration (cmc). The equilibrium surface tension of sodium naphthenate aqueous solutions was measured using pendant drop tensiometry and cmc was determined from plotting the equilibrium surface tension for a range of concentrations. Foam drainage and stability are characterized by visualization and analysis of thinning of single foam films of sodium naphthenate aqueous solutions over an extracted concentration range. This drainage by stratification (manifested as stepwise thinning) for sodium naphthenate solutions is shown to manifest as thinner circular domains of progressively darker shades of gray forming and growing within a thicker film, using the thin film balance technique and bubble pressed to a surface technique.