Summary
This paper describes successful practices applied during polymer flooding at
Daqing that will be of considerable value to future chemical floods, both in
China and elsewhere. On the basis of laboratory findings, new concepts have
been developed that expand conventional ideas concerning favorable conditions
for mobility improvement by polymer flooding. Particular advances integrate
reservoir-engineering approaches and technology that is basic for successful
application of polymer flooding. These include the following: (1) Proper
consideration must be given to the permeability contrast among the oil zones
and to interwell continuity, involving the optimum combination of oil strata
during flooding and well-pattern design, respectively; (2) Higher polymer
molecular weights, a broader range of polymer molecular weights, and higher
polymer concentrations are desirable in the injected slugs; (3) The entire
polymer-flooding process should be characterized in five stages--with its
dynamic behavior distinguished by water-cut changes; (4) Additional techniques
should be considered, such as dynamic monitoring using well logging, well
testing, and tracers; effective techniques are also needed for surface mixing,
injection facilities, oil production, and produced-water treatment; and (5)
Continuous innovation must be a priority during polymer flooding.
Introduction
China’s Daqing oil field entered its ultrahigh-water-cut period after 30
years of exploitation. Just before large-scale polymer-flooding application,
the average water-cut was more than 90%. The Daqing oil-field is a large
river-delta/lacustrine facies, multilayered with complex geologic conditions
and heterogeneous sandstone in an inland basin. After 30 years of
waterflooding, many channels and high-permeability streaks were identified in
this oil field (Wang and Qian 2002).
Laboratory research began in the 1960s, investigating the potential of
enhanced-oil-recovery (EOR) processes in the Daqing oil field. After a
single-injector polymer flood with a small well spacing of 75 m in 1972,
polymer flooding was set on pilot test. During the late 1980s, a pilot project
in central Daqing was expanded to a multiwell pattern with larger well spacing.
Favorable results from these tests--along with extensive research and
engineering from the mid-1980s through the 1990s--confirmed that polymer
flooding was the preferred method to improve areal- and vertical-sweep
efficiency at Daqing and to provide mobility control (Wang et al. 2002, Wang
and Liu 2004). Consequently, the world’s largest polymer flood was implemented
at Daqing, beginning in 1996. By 2007, 22.3% of total production from the
Daqing oil field was attributed to polymer flooding. Polymer flooding boosted
the ultimate recovery for the field to more than 50% of original oil in place
(OOIP)--10 to 12% OOIP more than from waterflooding.
At the end of 2007, oil production from polymer flooding at the Daqing oil
field was more than 10 million tons (73 million bbl) per year (sustained for 6
years). The focus of this paper is on polymer flooding, in which sweep
efficiency is improved by reducing the water/oil mobility ratio in the
reservoir. This paper is not concerned with the use of chemical gel treatments,
which attempt to block water flow through fractures and high-permeability
strata. Applications of chemical gel treatments in China have been covered
elsewhere (Liu et al. 2006).
© 2009. Society of Petroleum Engineers
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History
- Original manuscript received:
25 January 2008
- Meeting paper published:
20 April 2008
- Revised manuscript received:
4 September 2008
- Manuscript approved:
25 October 2008
- Published online:
1 June 2009
- Version of record:
1 June 2009
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