Experimental Observations of Foam Behavior

Callaghan and Neustadter [31] have made a study of the foam stabilities of air-crude oil and natural gas-crude oil systems using a variety of light crude oils of viscosities 14 mPa s. This study, at ambient temperature using a sparging method, concerned so-called dead oils from which natural gas had been separated. It also involved a comparison of the foam behavior with critical film rupture thicknesses, bulk phase, and surface shear viscosities together with dilatational surface properties. 

Here is the initial foam height, H, is the foam height at time t, and t is the time for total foam collapse, where aU quantities are relative to those at the situation immediately after sparging has ceased. A similar correlation was observed for the air-crnde oil system—the foam stability of which was lower than for the natural gas-crude oil system. The foam is seeu to be extremely unstable—collapsing with average lifetimes 45 s even with oils of viscosities up to an order of magnitude higher than that of water. 

Extremely viscous so-called heavy oils are often produced from wells in Canada, Venezuela, and China. These oils often have reported viscosities in the range of (3-30) x 10 mPa s [38 0] and are often produced at the well head as a gas-in-oil emulsion with a gas volume fractions of from 0.05 to 0.40 [41], which has the appearance of chocolate mousse [38]. The foams formed from such gas-in-oil emulsions upon standing can be extremely stable, persisting for several hours in open vessels [38]. 

FIGURE 10.4 Plot of total asphaltene + resin content against bulk shear viscosity at 38°C for a range of degassed crude oils from various fields. (After Poindexter, M.K. et al., Energy Fuels, 16, 700, 2002.) 

It is more than 30 years since Callaghan and Neustadter [4] made a study of oil foaming, which combined snrface rheological and thin film observations. Perhaps it is time this approach is revisited with some emphasis on the difficult issue of measurements on live crude oils at elevated temperatures. Such measurements could be combined with application of modern theories abont foam drainage, foam film drainage, and rupture (see Chapter 1 for a brief introduction to these topics). 

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