Feasibility Study of CO₂ Stimulation in the West Sak Field, Alaska

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.