4. Primary Recovery
Reservoir Energy Sources
Liberation, expansion of solution gas
Influx of water from aquifer
Expansion of reservoir rock into pore space
Expansion of original reservoir fluids
- Free gas
- Interstitial water
- Oil, if present
Gravitational forces
Petroleum Recovery
Processes
5
8. Primary Recovery
Rapid and continuous
pressure drop, rate of
decline falls at bubble
point pressure.
Rs (solution gas oil ratio)
low until p=pb, then
increases to maximum and
declines.
Absent or minimal water
influx (water cut).
Well production declines
rapidly, early pumping
required. Time
Pressure
GOR (R)
Rsi Water Cut
Petroleum Recovery
Processes
Solution-Gas Drive In Oil Reservoir
9
9. Primary Recovery
Estimating Oil Recovery Factors
Solution-gas drive - API study
( )
( )
m
-
f
=
1741
.
0
a
b
3722
.
0
wi
0979
.
0
ob
1611
.
0
ob
wi
R
p
p
S
k
B
S
1
8
.
41
E
Petroleum Recovery
Processes
10
10. Primary Recovery
Gas Cap Drive in Oil Reservoirs
Cross Section
Oil-producing well
Oil
zone
Oil
zone
Gas cap
Petroleum Recovery
Processes
11
11. Primary Recovery
Pressure drops continuously,
but slowly.
Rs (solution gas oil ratio)
increases continuously.
Water influx (water cut)
absent or minimal
Wells have long flowing
life (depending on the size
of the gas cap).
Pressure
GOR (R)
Rsi
Water Cut
Time
Petroleum Recovery
Processes
Gas Cap Drive In Oil Reservoir
12
12. Primary Recovery
Water Drive in Oil Reservoirs
Edgewater Drive
Oil-producing well
Water Water
Cross Section
Oil Zone
Petroleum Recovery
Processes
13
13. Primary Recovery
Water Drive in Oil Reservoirs
Bottomwater Drive
Oil-producing well
Cross Section
Oil Zone
Water
Petroleum Recovery
Processes
14
14. Primary Recovery
Pressure remains high,
small drop.
Rs (solution gas oil ratio)
remains low.
Water influx starts early
and increases to
appreciable levels.
Residual oil may be
trapped behind the
advancing water.
Wells flow freely until
water production (water
cut) becomes excessive
Pressure
GOR (R)
Rsi
Water Cut
Time
Petroleum Recovery
Processes
Water Drive In Oil Reservoir
15
15. Primary Recovery
Water Drive in Oil Reservoirs
Effect of Production Rate on Pressure
Time, years
2000
1900
1800 2
1
0 60
40
20
0
1700
20
15
10
5
0
Pressure,
psia
Oil
production,
Water
Cut,
%
Gas/oil
ratio,
MSCF/STB
MSTB/D
Reservoir pressure
Water
Gas/oil ratio
Oil
Production data - lower oil production rate
Petroleum Recovery
Processes
16
16. Primary Recovery
Estimating Oil Recovery Factors
Water drive - API study
( )
( )
m
m
-
f
=
-
2159
.
0
a
i
1903
.
0
wi
0770
.
0
oi
w
0422
.
0
oi
wi
R
p
p
S
k
B
S
1
9
.
54
E
-
Petroleum Recovery
Processes
17