Doe/netl-2012/1540 Mobility And Conformance Control For Carbon Dioxide Enhanced Oil Recovery (Co2-Eor) Via Thickeners, Foams, And Gels - U.s. Department Of Energy Page 171

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flood, while the remaining pressure increase was attributed to the foam. The Hall plot result
indicated that the polymer foam had a resistance factor about twice as large as the polymer +
surfactant pre-slug. Further, tracer monitoring and injection profile results indicated that the pre-
treatment range of velocities in the various layers became more uniform and the proportion of
fluids entering the least permeable zones increased notably (e.g., 16%–23% in the top 0.5 m of
the C26-G9 well) indicating the increased resistance of the foam and a more uniform injection
profile amongst the layers. The most promising results were related to the cumulative oil
production in the 12 production wells. Before the pilot, the combined oil and production rate
was 566 tons/day, only 23 tons/day of which were oil, and the water cut was 97.2%. Halfway
through the pilot, the combined oil and production rate was 704 tons/day, the oil production rate
was 36 tons/day, and the water cut was 94.9%.
PetroChina Daqing Oilfield Co.’s Sabei Field, Xing 7-1-33 and Bei 2-Ding 2-59 Well
Clusters; SAG Polymer Foam; Conformance Control [He et al., 2010].
The Daqing oilfield is a multi-layer, heterogeneous sandstone system in an inland basin. The
o
reservoir temperature of this 1,000 m deep formation is 45
C. Oil viscosity at reservoir
conditions range between 6 to 9 cP. The permeability of the sands reaches values as high as
1000 mD, and the Dykstra Parsons coefficient of permeability variation ranges from 0.4 to 0.7
[Dong et al., 2008]. During the late 1980s, a polymer flooding pilot was conducted at Daqing,
which ultimately led to the initiation of the world’s largest polymer flood in 1996. By the end of
2007, the polymer flood resulted in the production of more than 10 million tons (73 MM bbl.) of
oil per year for six consecutive years.
The main pay zone in Daqing has now been flooded for more than thirty years and is exhibiting
water-cut values greater than 90%. Reservoir studies indicated that foam flooding could be a
viable means of recovering the remaining oil in the main pay zone via improved sweep
efficiency, while recovery of oil from the less permeable zones could be accomplished via
conformance and mobility control. The Sabei field in Daqing was selected for a field pilot of
polymer-stabilized nitrogen foam flooding because of its particularly high water cut of ~96%
associated with the presence of very high permeability watered-out zones. A well cluster, Bei 2
Ding 2-59, in the eastern portion of Area Bei-3 of the Sabei field was selected for the pilot test to
assess conformance control and oil production response.
It was anticipated that a relatively small, near-wellbore nitrogen foam treatment would
effectively divert the subsequently injected nitrogen away from the thief zone, improve the
injection profile, increase oil production, and decrease water production [He, et al., 2010]. The
aqueous foaming solutions studied for this field contained 0.3–0.5wt% surfactant and 30–1,500
ppm of a polymeric stabilizer.
The Bei 2 Ding 2-59 polymer-stabilized nitrogen foam pilot was conducted from October 2005
to January 2006. The cluster is composed of two central production wells, three injection wells,
and seven corner production wells in the peripheral zone. The targeted sandstone formations, Pu
II and Gao I, are 900–1,200 m deep in these clusters with permeability values ranging from 140
–900 mD. The foam was injected into one well at a time, with a maximum injection period of
3
one month per well. The cumulative injection into the three injectors was 4,477 m
of the
140

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