Page 99 - Fundamentals of Enhanced Oil and Gas Recovery

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Enhanced Oil Recovery Using CO 2

3.2.2.3.2 Bati Raman Field, Turkey [54]
This field, which is the largest oil field in Turkey, was discovered in 1961 with an esti-
mated OOIP of 1850 million STB. It was found that the formation is limestone with
vertical and horizontal heterogeneity. At primary recovery, only 1.5% of OOIP was
produced due to the high oil viscosity. Water flooding was carried out for 7 years (i.e.,
1971 1978). Injecting 3.2 million bbl of water achieved only 5% of oil recovery.
ACO 2 immiscible flooding was planned with a gas containing 91% of CO 2 . The
injected CO 2 converted carbonate formation into water-soluble calcium bicarbonate.
As a result, pore volume and permeability were increased. CO 2 injection was carried
out in two phases. In the first phase, Huff and Puff was conducted from 1986 to
1988. Afterward, a WAG process was started in 1988.

3.2.2.3.3 Wilmington Field, United States [55]
The Wilmington field, located in Los Angeles, was discovered in 1936. This field is a
layered formation, which is somewhat arbitrarily divided into seven reservoirs located
at depths ranging from 2300 to 4800 ft. This formation contained a crude oil of

13 28 API, and temperature was in the range of 123 226 F throughout the reser-

voirs. Such a low gravity crude oil contained in this multilayered formation along
with many faults have created a significant technical and economic challenge to the
profitable recovery of a significant fraction of Wilmington’s original oil in place.
Therefore different EOR strategies were studied. Water flooding started in 1961 and
continued until the end of May 1980. Primary recovery and water flooding recovered
only 30% OOIP. Five other EOR processes—polymer flooding, caustic flooding,
micellar/polymer, CO 2 , and steam flooding—were then piloted in this field. Among
these process, CO 2 flooding showed a significant improvement.
The shallowest reservoir, Tar Zone, was chosen for pilot CO 2 injection. The
injected gas was composed of 85% carbon dioxide and 15% nitrogen. CO 2 was injected
in liquid state at the early stage of the project. However, it changed to gaseous state
later. The WAG technique was also employed to slow down gas breakthrough. The
CO 2 injection rate was kept in the range of 1000 1500 MSCF/D per well. The water
injection rate was held at 1000 B/D per well to avoid formation fracturing.

3.2.2.3.4 Forest-Oropouche Reserves, Trinidad [56]
Between the years of 1973 and 1990, four major CO 2 immiscible flood projects
(namely, EOR4, 26, 33, and 44) were implemented in Trinidad at Forest-Oropouche
reserves. The detailed reservoir data are presented in the relevant literature [56].
In the EOR 4 project, the primary recovery was about 21.3% of OOIP. A second-
ary gas flood recovered about 20% of OOIP. CO 2 injection was then started in 1986.
From 1992 to 1994, the average oil rate was around 60 BPD. From 1995 to 1998, the