Page 73 - Formation Damage during Improved Oil Recovery Fundamentals and Applications

Low-Salinity Water Flooding: from Novel to Mature Technology 55

A LSWF field trial, in tertiary recovery mode, was planned (based on
earlier core-flood test results) and conducted between 2007 and 2009 in
the Endicott oil field (Alaska) in a single reservoir zone where the water
cut was stabilized at 95% following saline water injection (Seccombe
et al., 2010, Lager et al., 2011). This trial involved a single injector-
producer well pair 1040 ft apart, with the producer monitored for
changes in water cut and ionic compositional changes. LSW injection
began in June 2008 and was detected in the producer well 3 months later,
and that LSW breakthrough coincided with water cut dropping from
95% to 92%. Over the course of about 1 year, 1.3 pore volumes of LSW
were injected in the field area leading to incremental oil recovery of 10%
for the pore volume swept by the trial. The tertiary mode LSWF was
expected to reduce the residual oil saturation from 41% to 28% with no
adverse production outcomes.
Not all core-flooding experiments and field tests have shown LSWF
to be of benefit. Skrettingland et al. (2011) conducted core-flooding
experiments and a single-well chemical tracer pilot study involving three
reservoirs (upper and lower Statfjord and Lunde formations) in the Snorre
field, offshore Norway. The Statfjord formations demonstrated incremen-
tal oil recovery from the core experiments of only about 2% for seawater
flooding and LSWF; whereas, the Lunde formation showed no improved
recovery. The field pilot test was carried out on the Upper Statfjord for-
mation, but recorded no change in oil saturation. It was concluded that
the initial wetting conditions of these reservoirs were probably
unsuitable for LSWF.
On the back of successful LSWF test outcomes at Endicott oil field
and other fields, BP in 2011 decided to apply its own proprietary brand
of the technique to some large-scale field developments (e.g., Mad Dog
Phase 2 and Clair Ridge) as early stage secondary-recovery mode
projects. In 2016 BP, ConocoPhillips, Chevron, and Shell initiated
production at about 120,000 bopd at the largest offshore LSWF project,
to date, in Clair Ridge oil field (offshore West of Shetland, UK). Clair
Ridge is expected to produce some 42 million barrels of additional oil,
contributing to a total of 640 million barrels of expected total oil recov-
ery (from about 8 billion barrels of oil in-place), at a relatively low cost
(BP, 2015). The d4.5- billion development includes around USD$120
million for the desalination facilities to supply LSW for “waterflooding”
from sea water.