Summary
Polymer-flooding technology has been used widely in the Daqing oil field of
China in recent years. To maintain the viscosity of a polymer solution, fresh
water typically is used to confect the polymer solution instead of produced
water. In doing so, a problem emerges--the produced water cannot be injected
completely into the stratum. The superfluous produced water has to be treated
to meet the requirements of discharge, which increases the cost of oil
production. In this study, the produced water is desalinated through the
implementation of of an electrodialysis principle. A set of experimental
equipment that can desalinate produced water at a capacity of 300
m3/d was established at a produced-water-treatment station in the
Daqing oil field. The experiment’s results indicate that the total salinity of
desalinated produced water can be less than 1000 mg/L. The polymer solution
confected with desalinated produced water has more statistically significant
characteristics than fresh water in that the viscosity increases by 63.5% and
the recovery rate increases by 4.5%. This experimental study will be beneficial
to keeping the balance of oily-water production and injection in oil fields.
This technology for produced-water desalination will have better application
prospects in the polymer-flooding process.
Introduction
In crude-oil extraction, water can be injected into the stratum to drive the
crude oil out. This is termed often as the water-flooding process. The oil
content will decrease after water-flooding is operated for some time. To
improve oil recovery, polymer flooding (injected water that contains polymer)
will be used subsequently, a process called enhanced oil recovery (Wang et al.
1999). Polymer-flooding technology has been used widely in the Daqing oil field
of China in recent years. The oil production by polymer flooding in the Daqing
oil field reached 10,000,000 tons in 2006, which is approxiamtely one-fourth of
the total annual oil production.
In the waterflooding process, the oily water produced from oil wells
(produced water) is used to inject back into the stratum after being treated.
This is beneficial to maintaining the balance of water injection and
production. The produced water has a high total salinity (TS), ranging usually
from 4,000 to 5,000 mg/L in the Daqing oil field. The metallic ions dissolved
in the produced water, such as Ca2+, Mg2+,
Na+, and K+ will result in the degradation of polymer,
thus lowering the viscosity of the polymer solution. Therefore, the produced
water cannot be used appropriately directly for polymer-solution confecting. To
maintain the viscosity of the polymer solution, fresh water is used to confect
polymer solution instead of produced water. However, a severe problem is
generated: The produced water cannot be injected into the stratum thoroughly.
The superfluous produced water must be treated to meet the requirements of
discharge, which will increase the cost of oil production. Furthermore, the
expense of buying fresh water is an additional cost burden for petroleum
companies (Hu et al. 1997).
In this study, the researchers attempt to desalinate the produced water
through the implementation of the electrodialysis principle. A set of
experimental equipment that can generate desalinated produced water at 300
m3/d was operated at a polymer-flooding produced-water-treatment
station in the Daqing oil field. Its performance was evaluated. The
characteristics of polymer solution confected with desalinated water were then
analyzed in a laboratory.
© 2009. Society of Petroleum Engineers
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History
- Original manuscript received:
29 July 2007
- Meeting paper published:
11 November 2007
- Revised manuscript received:
6 April 2008
- Manuscript approved:
7 May 2008
- Published online:
2 March 2009
- Version of record:
26 February 2009
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