Page 375 - Standard Handbook Petroleum Natural Gas Engineering VOLUME2
P. 375
Enhanced Oil Recovery Methods 341
I I ’ 111’1 I I ‘ ‘
Ill I 11111 ‘I I I
-NOT CRITICAL IF UNIFORM - HP GAS
HIGH ENOUGH FOR
GOOD INJECTION RATES co2
POLY MER
SUR FACTA NT
ALKALINE
IN-SITU
STEAM
Figure 5-178. Permeability ranges for EOR methods [386].
For completeness, we have included the two “last resort” methods (special
steamflooding techniques with shafts, fractures, drainholes, etc., and mining plus
extraction) are listed in Figure 5-176. These methods are not included in Figures
5-177 and 5-1 78 because these unconventional techniques are not considered in
most reservoir studies.
Figure 5-177 shows that those enhanced recovery processes that work well with
light oils have rather specific depth requirements. As discussed, each gas
injection method has a minimum miscibility pressure for any given oil, and the
reservoir must be deep enough to accommodate the required pressure.
Figure 5-178 shows that the three methods that rely on gas injection are the
only ones that are even technically feasible at extremely low permeabilities. The
three methods that use backup waterflooding need a permeability of greater
than 10 md in order to inject the chemicals or emulsions and to produce the
released oil from the rock. Although most authors show a minimum permeability
requirement of 20 md for polymers, we indicate a possible range down as low as
3 md for low molecular weight polymers, especially in some carbonate reservoirs.
The screening guides in the figures can perhaps be summarized by stating a fact
well-known to petroleum engineers: oil recovery is easiest with light oil in very
permeable reservoirs and at shallow or intermediate depths. Unfortunately, nature
has not been kind in the distribution of hydrocarbons, and it is necessary to select
the recovery method that best matches the oil and reservoir characteristics.