Appeal No. 2005-2446 Page 2
Application No. 09/951,099
“Production can be increased from such wells through oil well stimulation” which “typically
involves injecting a fracturing fluid into the well bore at extremely high pressures to create
fractures in the rock formation surrounding the bore.” Id., pages 1-2. The fracturing fluid
contains a water-soluble polymer, which provides appropriate flow characteristics to the
fluid, and also provides sufficient viscosity to suspend a non-compressible propping
agent, such as sand. The purpose of the propping agent is to keep the fractures open
once the pressure on the fracturing fluid is released – ideally producing a zone of high
permeability. Id., page 2. However, “[w]hen [the] pressure on the fracturing fluid is
released and the fracture closes around the propping agent, water is forced therefrom
and the water-soluble polymer forms a compacted cake . . . [which] can prevent oil or gas
flow if not removed. To solve this problem, [enzyme] ‘breakers’ are included in the
fracturing fluid” to degrade the water-soluble polymer, but their effective use “requires that
the onset of enzymatic hydrolysis be controlled” (id.).
“Particularly preferred [water-soluble polymers] are [ ] hydratable polysaccharides
having galactose and/or mannose monosaccharide components, examples of which
include the galactomannan gums, [and] guar gum[s]” (id., page 8) and the “[e]nzyme
breakers are typically ß-mannanases or ß-glucosidases” (id., page 12). “Enzymatic
attack on the polysaccharide chain can be controlled (arrested) by addition of a
complexing agent . . . [such] that the enzyme is inactive or essentially inactive prior to . . .
reducing the pH . . . of the fracturing fluid” (id., page 9). The complexing agent used to
control the activity of the enzyme breaker may be an aminoglycol or other substituted
glycol, for example, 2-amino-2-hydroxymethyl-1,3-propanediol (Tris).
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