Summary
Gelled polymer treatments applied in injection and production wells are used
to alter fluid flow in oil reservoirs so that oil production is increased and
water production is decreased. A common gel used in field treatments is made by
crosslinking partially hydrolyzed polyacrylamide (HPAM) with chromium acetate.
The initial step of the crosslink is the uptake of chromium acetate by a
carboxyl group on the HPAM. The kinetics of the uptake reaction was studied as
functions of the concentrations of chromium, HPAM, and hydrogen ions. The data
were regressed to derive a rate expression for the disappearance of unreacted
Cr(III) in the gelant.
Introduction
The application of crosslinked polymers gels for permeability modification
of petroleum reservoirs has been effective in improving displacement
efficiency, increasing crude oil production, and reducing water production. The
treatment of an injection well consists of injecting an aqueous solution
containing polymer and a crosslinker into the high-permeability zones or
fractures of the reservoir where the polymer and crosslinker react to form a 3D
gel network, reducing the effective permeability of these zones. Displacing
fluids injected after the treatment are diverted into the previously unswept,
low-permeability zones resulting in additional oil recovery and less water
production. Gel treatments applied in production wells can also reduce water
production and increase oil production, although the mechanisms are not as well
defined.
One widely used gel system is an aqueous solution of partially hydrolyzed
polyacrylamide (HPAM) and a chromium(III) salt. Chromium(III) forms a complex
ion in solution and reacts by a ligand-exchange reaction with the carboxylate,
or hydrolyzed, groups on the polymer molecules to form crosslinks resulting in
a network or gel. These reactions are described by
(Equation 1)
and
(Equation 2)
where L represents a ligand in the chromium complex and -CO 2 represents a
carboxylate group on a polymer molecule (P1 or P2). The first reaction of
polymer P1 with the chromium complex is called the uptake reaction. The
reaction of a second polymer, P2, with the chromium complex creates a crosslink
between the polymers and is termed the crosslink reaction.
© 2005. Society of Petroleum Engineers
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History
- Original manuscript received:
12 January 2004
- Revised manuscript received:
19 July 2005
- Manuscript approved:
20 July 2005
- Version of record:
15 September 2005
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