Iraqi Kurdistan All in the Timing

Rangely field, yielding just 10
barrels per day.
Almost 30 years after those
first disappointing wells were
drilled, Raven A-1 was spudded
by the California Company
(now Chevron) in 1931. It took
more than a year to drill down
to an oil saturated sandstone at
a depth of 1,931m. In 1933, the
well tested at 230 bopd from the
Weber sandstone and remained
shut in for 10 years after
producing 8,000 bo. The well
had discovered a huge field with
more than 1.9 billion barrels
oil-in-place, but it would take
World War II to increase the
demand for oil before the remote
field would be developed. Since
then, the field has undergone
a multitude of projects that
have slowed production decline
and greatly increased the overall oil
recovery. Chevron learned early on that to
effectively produce this complex reservoir,
they had to rely on the operations
personnel to closely monitor each well in
order to make timely adjustments to their
production programme.
Production History
Development drilling began in April
1944 and after just a year and a half,
182 wells had penetrated the productive
Weber sandstone. At one point in 1946,
54 rigs were operating simultaneously,
and by 1949, 478 wells on 40-acre
spacing (~0.16 km 2 ) had been drilled.
Produced gas injection began in 1950
to help maintain reservoir
pressure.
Further declines in
reservoir pressure led to a
full scale water flood operation
in 1958, with peak production
reaching 82,000 bopd. Infill drilling
started in the early 1970s. The water
flood continued until a tertiary
recovery programme using carbon
dioxide (CO 2 ) injection was initiated in
1986. Additional expansions and infill
drilling, including a pilot project testing
10-acre (~0.04 km 2 ) spacing, have
continued, with the most recent new
well drilled in 2013.
All of the secondary and tertiary
production programme s, as well as
A number of projects designed to bring more oil to the surface have kept the Rangely field economic for 70 years.
infill drilling, are designed to recover
additional oil-in-place and extend
the life of the field. The water flood
programme was carried out by drilling
additional wells where water is injected
into the reservoir, maintaining reservoir
pressure and pushing oil toward
production wells. The CO 2 injection
tertiary recovery programme resulted
in some surprises and a change in the
original design plans.
The Rangely CO2 Project
Before starting tertiary recovery at
Rangely, Chevron expected to recover
821 MMbo with the water flood – about
CO 2 injection started in the pink circle and has expanded out
across the field during the past 30 years.
Chevron
43% of the 1.9 Bbo originally in place.
They also expected to gain another
118 MMbo by adding CO 2 injection.
(Note: The field is still going strong,
producing 11,000 bopd and 1,200 bpd
NGLs.) Chevron had a large net gain in
production but also one that required
the investment of millions of dollars.
Operating costs increased as CO 2
reacted with water to form carbonic
acid, necessitating all the equipment
used in producing this field to be
corrosion resistant.
The CO 2 is purchased from a gas
sweetening plant near La Barge in southwest
Wyoming and is transported 77 km
Chevron
GEOExPro November 2015 75