Page 435 - Fundamentals of Enhanced Oil and Gas Recovery

Microbial Enhanced Oil Recovery: Microbiology and Fundamentals 423

The IFT between the mineral oils and water is typically in the range of the
35 60 mN/m [60]. Rhamnolipid and lipopeptides biosurfactants can reduce the
IFT between the hydrocarbon and water phases as low as 0.1 mN/m or even lower
[51 53,433,524,536,539,550,551]. It is reported that in comparison with synthetic
surfactants, rhamnolipid was proved to be 20 times more effective in solubilizing
hexadecane [436] and could mobilize 75% of the residual hexadecane from the
sand-packed columns [430,552] but a large number of pore volume of 40 70 was
required. A glycolipid biosurfactant showed great resistance to harsh condition and

was stable at temperatures as high as 120 C, pH range of 2 12, and salinity up to
10%. [553]. Comparing lipopeptide and rhamnolipid, the effective concentration of
the former is much lower [17,554]. Lipopeptides are reported to be able to reduce
the surface tension of water from 72 to 27.9 mN/m at a CMC of 0.017 g/L [555].
A report by Banat [556] indicates up to 95% oil recovery from sand-packed
columns. McInerney et al. [17] recounted about the effectiveness of lipopeptide pro-
duced by Bacillus mojavensis strain JF-2 in mobilizing large amounts of oil from sand-
packed columns in low concentrations and in less than one pore volume injection
containing about 900 mg of biosurfactant/liter. Lipopeptides can function in reser-

voir harsh condition of temperatures as high as 100 C, pH range of 6 10 and salt
concentrations as high as 8% [404,450,557,558]. Many laboratory experiments
have been done to evaluate the effect of biosurfactants on recovering residual
oil [124,387,393,412,444,450,451,457,462,467,531,540,543 545,550,553,556 584].
Moreover, several patents have been issued, a list of which is presented in Table 10.3.
As it was mentioned before, bioemulsifiers are high molecular weight amphiphilic
compounds produced by different microorganisms [182,606], the role of which is
establishing stable emulsion with hydrocarbons usually as the form of oil-in-water and
less commonly vice versa [6,182]. Despite the low molecular biosurfactant, the high
molecular weight ones, i.e., bioemulsifiers are not likely to reduce the IFT [182,607].
Bioemulsifiers are adequately effective in low concentrations just as biosurfactants
[182]. The most common bioemulsifier is emulsan, which is an anionic heteropoly-
saccharide and protein complex [6]. It is reported that emulsan just emulsifies the
hydrocarbon mixtures rather than the pure hydrocarbons [547,548].
Biosurfactant can be used for several other purposes [441,608], including separat-
ing the oil from the bottom of the tanks [609,610] and bioremediation (such as
removing the crude oil from the oil-contaminated soil [541,611,612]). Bioemulsifier
may have many different roles in petroleum industry other than MEOR such as
emulsion-based fuels, emulsion-facilitated petroleum transport, oil tank clean-up, pre-
venting paraffin deposition, and environmental protection and remediation
[17,182,457,540,607,613], which are none of this study’s concerns.