Page 364 - Standard Handbook Petroleum Natural Gas Engineering VOLUME2

330 Reservoir Engineering

A steeply dipping formation is very desirable to permit some gravity
stabilization of the displacement which normally has an unfavorable mobility
ratio.
Problems.

Viscous fingering results in poor vertical and horizontal sweep efficiency.
Large quantities of expensive products are required.
Solvent may be trapped and not recovered.

Nitrogen and Flue Gas Flooding [a861
Description. Nitrogen and flue gas flooding are oil recovery methods which
use these inexpensive nonhydrocarbon gases to displace oil in systems which
may be either miscible or immiscible depending on the pressure and oil
composition. Because of their low cost, large volumes of these gases may be
injected. Nitrogen or flue gas are also considered for use as chase gases in
hydrocarbon-miscible and CO, floods.

Mechanisms. Nitrogen and flue gas flooding recover oil by:
Vaporizing the lighter components of the crude oil and generating mis-
cibility if the pressure is high enough.
Providing a gas drive where a significant portion of the reservoir volume
is filled with low-cost gases.

Teehnierrl Screenhg Guides
Cmde oil
Gravity >24" API (>SSo for nitrogen)
Viscosity e10 cp
Composition High percentage of light hydrocarbons (C,-C,)
RssnVoiT
Oil saturation >SO% PV
Type of formation Sandstone or carbonate with few fractures
and high permeability streaks
Net thickness Relatively thin unless formation is dipping
Average permeability Not critical
Depth r1.500 ft
Temperature Not critical
Llmitatlons.

Developed miscibility can only be achieved with light oils and at high
pressures; therefore, deep reservoirs are needed.
A steeply dipping formation is desired to permit gravity stabilization of the
displacement which has a very unfavorable mobility ratio.

Problems.
Viscous fingering results in poor vertical and horizontal sweep efficiency,
Corrosion can cause problems in the flue gas method.
The nonhydrocarbon gases must be separated from the saleable produced
gas-