The West Sak Field is estimated to contain 25 billion barrels of heavy oil-in-place. Like Prudhoe Bay field, which contains 23 billions barrels of oil-in-place, the West Sak is potentially another super-giant filed located on the North Slope of Alaska. The West Sak crude oil of 14 – 22.5 °API gravity lies at depths ranging from 2500 to 4500 feet below sea level.
A waterflood pilot conducted by ARCO Alaska, Inc. in 1984-86 showed that the recoverable reserves by primary and waterflooding methods would be very low because of the absence of a natural drive mechanism in the West Sak Field and the high reservoir oil viscosity which ranges from 50 to 3000 cp. Thus, the field is considered a target for enhanced oil recovery (EOR) processes. A preliminary EOR screening study showed that CO2 stimulation is a promising EOR process for the West Sak oil field. The CO2 required for cyclic stimulation can be obtained from the natural gas of the nearby Prudhoe Bay field which contains approximately 12% CO2.
In this paper, cyclic CO2 stimulation in the West Sak field is investigated using numerical simulator. The objectives of the study are: (1) to evaluate the performance of the cyclic CO2 stimulation versus primary depletion in the West Sak; (2) to perform a sensitivity study in order to identify the parameters governing the CO2 stimulation process, and predict the effects of these parameters on oil recovery, including such parameters as CO2 slug size injected per cycle, number of cycles, length of soak period, back pressure during production, oil and gas saturations; and (3) to determine the feasibility of CO2 stimulation process to improve the recovery of oil from the West Sak sands.