CO2-Enhanced
Oil Recovery Program in Citronelle Field, Southwest Alabama
presented by
Jack Pashin
Director, Energy Investigations Program,
Geological Survey of Alabama
ABSTRACT
Citronelle Field is developed at the crest
of Citronelle Dome, which is a giant salt-cored anticline in
the eastern Mississippi Interior Salt Basin of southwest Alabama.
More than 169 million barrels of 42-46° gravity oil have
been produced from the Lower Cretaceous Donovan Sand in Citronelle
Field. Production has declined significantly, but CO2-enhanced
recovery operations have strong potential to revitalize the field.
Citronelle Dome is located near a major coal-fired power plant,
and major capacity exists for the sequestration of CO2 emissions
from the power plant in saline reservoirs between the Donovan
Sand and the Cretaceous chalk of the Selma Group.
Citronelle Dome is an elliptical structure in plan view that
forms a simple four-way structural closure with limbs dipping
less than 3°. The Donovan oil accumulation is sealed by a
thick succession of shale and anhydrite with the oil-water contact
being more than 100 feet above the structural spill point of
the dome. The Donovan Sand is extremely heterogeneous and contains
a multitude of oil accumulations in stacked marginal-marine sandstone
bodies. The thickness of individual pay zones typically ranges
from 2 to 25 feet. Individual sandstone bodies are aggradational
deposits, and the Donovan interval can be subdivided into two
retrogradational sequence sets. Approximately 37 percent of the
original oil in place has been recovered by primary and secondary
methods, and CO2-enhanced oil recovery has the potential to increase
reserves by up to 20 percent.
A 5-spot well pattern in the northeastern part of Citronelle
Field is being developed for a pilot program in which 15,000
tons of CO2
will be injected. Injection will take place simultaneously into
two sandstone units and will be performed as a water-alternating-gas
(WAG) program. The injection well is located in a thin area in
the two target sandstone units, and the thickest pay sections
are in the eastern part of the well pattern. CO2 will be injected in
two slugs of 7,500 tons, and baseline reservoir simulations indicate
that this injection will result in a nearly four-fold increase
of the oil production rate in the pilot area. Based on modeling
results, continuous injection of 115 kilotons of CO2 will maximize
sweep of the pilot area and can potentially increase the maximum
oil production rate of the 5-spot pattern from less than 40 to
nearly 600 barrels per day.
BIOGRAPHY
Jack Pashin
is director of the Energy Investigations Program of the Geological
Survey of Alabama. He received a Ph.D. in Geology from the University
of Kentucky in 1990. His primary research focus is petroleum
geology, coal geology, and carbon sequestration. Dr. Pashin has
published extensively and has received numerous awards for his
research. He currently serves on the editorial boards of the
AAPG Bulletin and the International Journal of Coal Geology and
is Vice Chair of the Coal Geology Division of the Geological
Society of America. |