American Oil and Gas Reporter - February 2015 - 90

SpecialReport: Improved Oil Recovery
altered the wetting state of Bakken cores
toward water-wet, and also consistently
imbibed to displace significantly more oil
than brine alone. Thus, imbibition of surfactant formulations appears to have substantial potential to improve Bakken oil
recovery. A 2010 analysis, "Bakken Formation Reserves Estimates," by Julie
LeFever and Lynn Helms at the North
Dakota Department of Mineral Resources,
demonstrates the Bakken's uncertain recovery factors during primary recovery
operations, but values of only 3-10 percent
original oil in place have been suggested.
Three of the surfactant imbibition tests
provided EOR values of 6.8-10.2 percent
OOIP, incremental over brine imbibition.
Ten surfactant imbibition tests provided
EOR values of 15.7-25.4 percent OOIP.
· Most surfactant tests were performed
on cores from the Bakken's middle member. However, cores from the Upper
Bakken showed responses to surfactant
imbibition consistent with those observed
in the Middle Bakken. In particular, upper
shale cores provided EOR values of 15.8
percent OOIP, 8.1 percent OOIP, and
21.6 percent OOIP, respectively.

· Incremental recoveries from the
preserved cores ranged from 6.8 percent
to 25.4 percent OOIP. This is effectively
the same range found in cleaned cores.
The surfactants examined in the work
(amphoteric dimethyl amine oxide, nonionic ethoxylated alcohol, anionic internal
olefin sulfonate, and anionic linear olefin sulfonate) were selected because
they performed better during preliminary
studies. However, the experiments did
not make it clear if any surfactant performed definitively better than the others.
On the whole, all show potential to provide
FIGURE 2

Laboratory Setup
Nitrogen gas

Input pressure
Valve A

Liquid out
Hassler
cell

ULTRA-FLOW®
Plastic vessel

CENTRALIZERS/
PARAFFIN SCRAPERS

Full-circle Wiping
of Tubing I.D.

Valve B

FIGURE 3
Oil Recovery Comparison at Optimal Salinity
And Formation Water Salinity at 120 Degrees C

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90 THE AMERICAN OIL & GAS REPORTER

Oil Recovery Factor of OOIP (%)

Positive Wear
Indicators

Overburden pressure
ISCO pump

Temperature bath

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Force on Sucker Rods

Longer Useful LIfe
from Longer Vanes
& Bearing Surfaces

Output pressure

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positive recovery values.
So far, the UND research group has
shown that ordinary brine can drive out
small quantities of oil from shale, though
not enough for commercial success.
Achieving high oil recovery rates requires
the right surfactant, proper salt content,
correct pH, and effective temperature. At
the optimal salinity, the incremental oil
recovery (during imbibition into Bakken
cores at 120 degrees C) can be 18 percent
OOIP higher than for comparable experiments using formulations with 15-30
percent TDS, and the average instanta-

20
A, Optimal Salinity
A, Formation Water Salinity
B, Optimal Salinity
B, Formation Water Salinity

0
1

100
Dimensionless Time

1,000

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American Oil and Gas Reporter - February 2015

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