Summary
Water production during oil and gas recovery is a longstanding problem that
is becoming critical with maturing fields worldwide. Lifting, processing,
treating, and reinjection of the unwanted water add to the overall oil
production costs. Also, water disposal may pose environmental problems. Recent
statistical studies indicate that processing unwanted water costs the oil
industry nearly U.S. $40 billion per year.
Polymer gels have been widely used as blocking agents for excessive water
production. In this study, two different polymers were crosslinked with
polyethyleneimine (PEI). The first is a copolymer of polyacrylamide tert-butyl
acrylate (PAtBA), and the second is a polyacrylamide (PAM). The PAtBA/PEI
system was previously shown to be stable at temperatures up to 160°C, typical
of those encountered in deep oil and gas reservoirs. However, the crosslinking
mechanisms of this system at high temperatures have not been well defined.
This study examined the structural changes of PAtBA using C-13 nuclear
magnetic resonance (NMR) spectroscopy. Understanding these changes is a first
step toward the identification of the crosslinking mechanisms of PAtBA and PAM
with PEI. This will have a strong impact on the design of water shutoff
treatments utilizing these systems.
Introduction
As oil and gas fields mature, larger volumes of water are produced.
Separating, treating, and disposing this water add extra costs to the petroleum
production. It has been reported that the petroleum industry spends several
tens of billions of dollars to deal with excessive water production (Bailey et
al. 2000).
Hydrophilic polymer gels have been widely used to reduce (Zaitoun and Kohler
1988) or completely block (Hutchins et al. 1996.water from its producing zones.
Polyacrylamides have been the most commonly used base polymers crosslinked with
either inorganic or organic crosslinkers. Inorganic crosslinkers include Cr+3,
Al+3, and Zr+4 and have been mostly utilized to crosslink partially hydrolyzed
polyacrylamide (HPAM). Inorganically crosslinked gels result from the ionic
bonding between the negatively charged carboxylate groups and the multivalent
cation (Prud'homme et al. 1983; Lockhart 1994; te Nijenhuis et al. 2003).
Organic crosslinkers were introduced to obtain gels that are stable over a
wider temperature range (Moradi-Araghi 1991; Albonico et al. 1994; Hardy et al.
1999). This is possible because in this case, the crosslinking is done by a
covalent bonding, which is much more stable than ionic bonds. The covalent
bonds often involve the amide groups on the polymer backbone. A typical example
of an organically crosslinked gel is the polyacrylamide-phenol/formaldehyde
system, which has been reported to be stable at 121 DEGREE C for 13.3 years
(Moradi-Araghi 2000, 1993). However, its toxicity has limited its broad use in
the field. Chemical alternatives for the phenol/formaldehyde system were also
reported (Moradi-Araghi 1994; Dovan et al. 1997).
© 2006. Society of Petroleum Engineers
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History
- Original manuscript received:
6 September 2005
- Revised manuscript received:
28 June 2006
- Manuscript approved:
5 July 2006
- Version of record:
20 December 2006
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