Page 438 - Fundamentals of Enhanced Oil and Gas Recovery

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10.10.2 Biopolymers
Bacteria within the reservoir tend to produce surface molecules in the form of bio-
polymers [31]. The majority of these metabolic biopolymers are exopolysaccharides,
which can promote the cell adhesion to the surface and prevent desiccation and pre-
dation of the bacteria [17,43,391,409,614 618].
Biopolymers can act as the bioplugging agent as the biofilms. Generally, biofilms
are composed of exopolysaccharides bound clusters of cells, which can induce clog-
ging effects [22]. The metabolically generated biopolymers can be favorably used for
selective plugging and modifying the permeability profile within the reservoir and also
reducing the viscous fingering of waterflood [17,19,21,42,124,391,422,616,617,
619 635]. In addition to the laboratory experiments, application of biopolymers on
diverting the waterflood from the high-permeable to the low-permeable zones has
been tested in fields too [617,619,620,636 638]. Microbial plugging is usually associ-
ated with supplying nutrients to microorganisms either injected or exogenous
[15,21,616,628,639]. The injected fluid including the microorganisms and/or nutri-
ents tends to flow through the more permeable pathways. The provided nutrients
stimulate the microorganisms to grow and this would decrease the permeability of
region that once were highly permeable and consequently modify the permeability
profile. It is likely that in situ production of biopolymers plugs the useful pore and
consequently results in formation damage. Just as the case for biosurfactants, a sign of
bioemulsifier generation is alteration of some characteristics of the crude oil such as
viscosity, cloud point, and pour point [6,452 455].
Table 10.4 lists the major biobiopolymers used in MEOR along with the produc-
ing microorganisms. Two important biopolymers are xanthan gum [624,640 642]
and relatively less effective, curdlan [643] (a high-molecular-weight polymer of glu-
cose) [4]. The other reported biopolymers are levan [621], pullulan [622], dextran
[617], scleroglucan [24,617,619,634,644]. Polysaccharides such as xanthan gum have
thickening effect in waterflooding (increase the drive water viscosity). This thermally
stable heteropolysaccharide can be produced by several Xanthomonas species via fer-
menting carbohydrates [15,24]. The efficiency of this biopolymer has been validated
in laboratorial studies [626,637,645,646]. The properties making the xanthan gum an
ideal polymer for EOR applications include its suitable viscosity, temperature, and salt
tolerance, and also being shear resistant [15,623,624,647]. The disadvantages are being
relatively expensive and its susceptibility for bacterial degradation [15,619,644].
Curdlan develop an insoluble gel in lower pH values as it is soluble in alkaline pH
[620,632,648 650]. Khachatoorian et al. [651] tested the effect of a number of bio-
polymers in reducing the permeability of the flow system in a sand-packed column
and they concluded that the poly-β-hydroxybutyrate has been the most effective than
the others (xanthan gum, guar gum, polyglutamic acid, and chitosan). More details