Page 370 - Standard Handbook Petroleum Natural Gas Engineering VOLUME2

336 Reservoir Engineering

Mechanisms. Steam recovers crude oil by:
Heating the crude oil and reducing its viscosity
Supplying pressure to drive oil to the producing well
Technical Screening Guida
CTerde oit
Gravity <25O API (normal range is 10”-25O API)
Viscosity >20 cp (normal range is 100-5,000 cp)
Composition Not critical but some light ends for steam
distillation will help
Reseruoir
Oil saturation >500 bbvacre-ft (or >40%50% PV)
Type of formation Sand or sandstone with high porosity and
permeability preferred
Net thickness >20 feet
Average Permeability >ZOO md (see transmissibility)
Transmissibility >lo0 md ft/cp
Depth 500-5,000 ft
Temperature Not critical
Limitations.

Oil saturations must be quite high and the pay zone should be more than
20 feet thick to minimize heat losses to adjacent formations.
Lighter, less viscous crude oils can be steamflooded but normally will not
be if the reservoir will respond to an ordinary waterflood.
Steamflooding is primarily applicable to viscous oils in massive, high
permeability sandstones or unconsolidated sands.
Because of excessive heat losses in the wellbore, steamflooded reservoirs
should be as shallow as possible as long as pressure for sufficient injection
rates can be maintained.
Steamflooding is not normally used in carbonate reservoirs.
Since about one-third of the additional oil recovered is consumed to
generate the required steam, the cost per incremental barrel of oil is high.
A low percentage of water-sensitive clays is desired for good injectivity.
Problems.

Adverse mobility ratio and channeling of steam.
Criteria for Gas Injection

For LPG slug or solvent flooding, enriched (condensing) gas drive, and high
pressure (vaporizing) gas drive, a range of pressures (and therefore, depths) are
needed to achieve miscibility in the systems. Thus, there is a minimum depth
requirement for each of the processes as shown earlier (see section on “Hydre
carbon Miscible Flooding”). The permeability is not critical if the structure is
relatively uniform; permeabilities of the reservoirs for the current field projects
range from less than 1 md to several hies [403]. On the other hand, the crude
oil characteristics are very important. A high-gravity, low-viscosity oil with a high
percentage of the C,-C, intermediates is essential if miscibility is to be achieved
in the vaporizing gas drives.