Page 259 - Standard Handbook Petroleum Natural Gas Engineering VOLUME2
P. 259
448 Reservoir Engineering
1200
-/
-0- 95% confidence limits of et’ z
2 1000 single reservoir pra d iction *.
z
\ ------ 95% confidence limits
000 of average raaervoir /.c/ a:
prad ict ion ’ m
-J 0
6 600 *-Correlation 0
P equation
W -
K 400
W
>
s 200
W 0 -/-
U
0
0 400 600 I200 1600 2000
OOIP, B/NAF
Figure 5-1 39. Correlation of primary oil recovery for water-drive reservoirs [239].
saturations, (2) volumetric equations if residual oil saturation and oil formation
volume factor at abandonment are known or estimated, and (3) decline curve
analysis, if production history is available. Each of these methods for estimating
primary oil recovery and gas recovery, when appropriate, will be discussed in
the following sections.
Primary Recovery Factors in Solution-Gas-Drive Reservoirs
Primary recovery from solution-gas-drive reservoirs depends on: type of
geologic structure, reservoir pressure, gas solubility, f hid gravity, f hid viscosity,
relative permeabilities, presence of connate water, rate of withdrawal, and
pressure drawdown. From a statistical study [244,245] the primary recovery
factors in Table 5-30 were obtained for different oil gravities and solution gas-
oil ratios in sands sandstones, limestones, dolomite, and chert. Based on work
of the same type in 135 reservoir systems, Wahl [246] presented a series of
figures that can be used to estimate primary recovery. One of these figures,
for a condition of a 2 cp reservoir oil and a 30% connate water saturation, is
reproduced in Figure 5-140. To use these figures the following is required oil
viscosity at reservoir conditions, interstitial water saturation, bubble-point
pressure, solution gas-oil ratio at the bubble-point pressure, and formation
volume factor.
MATERIAL BALANCE AND VOLUMETRIC ANALYSIS
Methods of estimating hydrocarbons in place by volumetric methods were
discussed. These estimates can be confirmed and future reservoir performance
can be predicted with the use of material balance equations. In the most
elementary form the material balance equation states that the initial volume in
