Page 365 - Standard Handbook Petroleum Natural Gas Engineering VOLUME2

Enhanced Oil Recovery Methods 331

Carbon Dioxide Floodlng [386]
Description. Carbon dioxide flooding is carried out by injecting large quantities
of CO, (15% or more of the hydrocarbon PV) into the reservoir Although CO,
is not truly miscible with the crude oil, the CO, extracts the light-to-intermediate
components from the oil, and, if the pressure is high enough, develops mis-
cibility to displace the crude oil from the reservoir.

Mechanisms. CO, recovers crude oil by:

Generation of miscibility
Swelling the crude oil
Lowering the viscosity of the- oil
Lowering the interfacial tension between the oil and the C0,-oil phase in
the near-miscible regions.

Technical Screening Guides
Crude oil
Gravity >26" API (preferably >30°)
Viscosity e15 cp (preferably e10 cp)
Composition High percentage of intermediate
hydrocarbons (C5-C,J, especially C,-C,,
Reservoir
Oil saturation >30% PV
Type of formation Sandstone or carbonate with a minimum of
fractures and high permeability streaks
Net thickness Relatively thin unless formation is steeply
dipping.
Average permeability Not critical if sufficient injection rates can
be maintained.
Depth Deep enough to allow high enough pressure
(> about 2,000 ft), pressure required for
optimum production (sometimes called
minimum miscibility pressure) ranges from
about 1,200 psi for a high gravity (>30"
API) crude at low temperatures to over
4,500 psi for heavy crudes at higher
temperatures.
Temperature Not critical but pressure required increases
with temperature.

Limitations.

Very low viscosity of CO, results in poor mobility control.
Availability of CO,.

Problems.
Early breakthrough of CO, causes several problems: corrosion in the
producing wells; the necessity of separating CO, from saleable hydro-
carbons; repressuring of CO, for recycling; and a high requirement of CO,
per incremental barrel produced.