Summary
This paper investigates the potential of various approaches for improving
sweep in parts of the Daqing oil field that have been enhanced-oil-recovery
(EOR) targets. Our studies indicated that the polymer flood should have
provided excellent sweep throughout the vast majority of the patterns under
consideration. However, because alkaline/surfactant/polymer (ASP) flooding is
being considered to increase recovery efficiency from the Daqing oil field,
mobility control and sweep improvement will be especially important and
challenging during implementation of any future ASP process.
Fractures were present in a number of Daqing wells (both injectors and
producers). Because the fractures were narrow and far from the wellbore, severe
channeling did not occur. On the contrary, fractures near the wellbore aided
reservoir sweep. Near-wellbore fractures increased the injectivity index
substantially during the injection of polymer solutions and increased
oil-productivity index in the production wells. These observations may be
valuable during implementation of future floods where very-low-mobility
chemical (i.e., ASP) banks must be injected to maintain mobility control.
Several modes of polymer degradation were considered, with mechanical
(shear) degradation being of greatest concern. Appropriate use of near-wellbore
fractures may mitigate mechanical degradation effectively, as well as improving
injectivity.
Several new polymers show potential for cost-effective improvements at
Daqing. Increased polymer concentration was also considered. A number of other
approaches are (or have been) under investigation, including colloidal
dispersion gels, foams, ASP foams, steam, microbes, and polymer solutions
prepared with reduced salinity.
Introduction
Laboratory research began in the 1960s, investigating the potential of EOR
processes in the Daqing oil field. The use of polymer flooding was identified
as a key method to improve areal and vertical sweep efficiency, as well as
providing mobility control (Wang 1995). Consequently, the world’s largest
polymer flood was implemented at Daqing, beginning in 1996 (Wankui et al. 2000,
Wang et al. 2002). By 2004, 22.7% of total production from the Daqing oil field
was attributed to polymer flooding. Polymer flooding should boost the ultimate
recovery for the field to more than 50% of original oil in place (OOIP), which
is 10% OOIP more than from waterflooding.
ASP flooding also has experienced extensive laboratory testing in China. The
ASP technique was gradually perfected for application at Daqing and has been
pilot tested on a large scale (Wang et al. 1999; Jirui et al. 2001; Wang 2003).
Results from two typical pilot tests in the south and north parts of the Daqing
field revealed incremental-oil-recovery values as high as 20% OOIP. By the end
of 2003, the Center Xinger pilot site showed a definitive increase in oil
production and decrease in water cut. In the east area of this site (the
largest portion included within the ASP pattern area), the predicted EOR was
approximately 18% OOIP more than from waterflooding.
Although field tests of polymer and ASP flooding have been very successful
at Daqing, concerns about sweep efficiency persist—particularly the possibility
of channeling expensive chemical formulations through the reservoir. Therefore,
the sweep efficiency at Daqing is receiving intense scrutiny, and possibilities
for improvement are being considered. In this paper, we examine the nature of
reservoir sweep in parts of the Daqing oil field that have been EOR targets. We
investigate the potential of various approaches for improving sweep. Our
objective is to establish better options in the future for improving sweep in
the main producing zone.
© 2008. Society of Petroleum Engineers
View full textPDF
(
2,521 KB
)
History
- Original manuscript received:
25 January 2007
- Meeting paper published:
22 April 2006
- Revised manuscript received:
10 June 2007
- Manuscript approved:
19 June 2007
- Version of record:
25 February 2008
View Cart
