Page 289 - Standard Handbook Petroleum Natural Gas Engineering VOLUME2
P. 289
456 Reservoir Engineering
should be measured to calibrate the instrument. Once the contour areas have
been planimetered, the net pay volume can be calculated in several ways. If the
number of contour intervals is even, the volume can be calculated by Simpson's
rule [272]:
(5-197)
where V, = reservoir volume, acre-ft
h = contour interval, ft
yo = area on top of sand minus area on base of sand at the highest
contour
yn = area on top of sand minus area on base of sand at the lowest
contour
When the number of contours is uneven, the volume can be found using the
slightly less accurate trapezoidal method
(5-198)
Once the reservoir volume is known, the oil in place, N, in stock tank barrels
is calculated by an equation similar to that given earlier:
7,758V0 (1 - S, )
N= (5-199)
BO
where N = reservoir oil initially in place, STB
7,758 = number of barrels/ acre-ft
Vo = net producing reservoir volume, acre-ft
Bo = oil formation volume factor, RB/STB
S1 = interstitial water saturation, fraction
I) = formation porosity, fraction
Similarly gas-in-place, G, in thousands of standard cubic feet, is estimated by
an expression similar to that given earlier:
43,560Vg+(1 - S,)pT,
G= (5-200)
ZTP,
where G = gas in place, scf
Vg = gas bearing volume of reservoir, acre-ft
ps = standard pressure, psia
T = reservoir temperature, degrees absolute
T, = standard temperature base, degrees absolute
z = gas deviation factor at reservoir conditions
Volumetric analysis yields the total hydrocarbon content of the reservoir; this
figure must be adjusted by a recovery factor to reflect the ultimate recoverable
reserves. Recovery factors are based upon empirical correlations, experience,
or analogy.