## Transcribed Text

Question 1
A volumetric gas field has an initial pressure of 4200 psia, a porosity of 17.2%, and connate
water of 23%. The gas volume factor at 4200 psia is 0.003425 cu ft/SCF and at 750 psia it
is 0.01852 cu ft/SCF.
a. Calculate the initial in-place gas in standard cubic feet on a unit basis.
b. Calculate the initial gas reserve in standard cubic feet on a unit basis, assuming an
abandonment pressure of 750 psia.
c. Explain why the calculated initial reserve depends on the abandoned pressure selected.
d. Calculate the initial reserve of a 640-acre unit whose average net productive formation
thickness is 34 ft, assuming an abandonment pressure of 750 psia.
e. Calculate the recovery factor based on an abandonment pressure of 750 psia.
Question 2
a. Consider the following reservoir explored and developed using two wells
Based on the logs at wells W1 and W2, a fault is determined that seals the reservoir in
the north. From expert geological interpretation, it is determined that the reservoir is
dome shaped. The contour plot of depth to layer top has circular shaped contour lines.
The cross-section of the reservoir is ellipse shaped.
Both wells W1 and W2 do not intersect the GWC. A Drill Stem Test was performed
on the well W1 and the reservoir pressure at a depth of 7053.5ft was determined to be
3200 psi. The specific gravity of the gas was determined to be 0.7. Using this
information and assuming air = 16.457 lb/cu.ft and a normal pressured reservoir, with
hydrostatic pressure given by:
Pw = 0.45 D + 14.8 where D is the depth in ft.
And correspondingly: Pg =
D C
dD
dP
gas
where C is a constant
Determine the depth to the Gas Water contact.
Given the contour plots above and the cross-section compute the bulk volume of the
reservoir (i.e. the volume upto the Gas Water Contact). For this task you need to use
the trapezoid equation with areas A1, A2 etc.. are areas of the half-circle in the contour
plot. In order to compute the radii of these circles you will need to use the cross-section
W1
W2
Depth7043.5 ft.
7083.5
ft.
7073.5
ft.
7063.5
ft.
7053.5
ft.
727 ft
40
N ft
GWC =
?
Ellipse
shaped
7043.5
ft. W1
a
b
plot and the fact that the cross section is a ellipse. Equation of an ellipse:
1
2
2
2
2
b
y
a
x
where a is the major axis (see figure) and b is the minor axis (see figure).
Given the following production data:
Pressure
(psia)
Cumulative Gas
Production MM SCF
Gas Volume Factor
cu. Ft/SCF
3200 0 0.0052622
2925 79 0.0057004
2525 221 0.0065311
2125 452 0.0077360
The initial average reservoir pressure is 3200 psia and the bottom hole temperature is
220oF. Standard conditions are 14.7 psia and 60oF.
a) Calculate the initial gas in place using the production data at the end of each
production interval, assuming volumetric behaviour.
b) Do the calculated Gas in place indicate a water drive
c) Show that a water drive exists by plotting the cumulative production vs. P/z
d) Using the material balance equations for water influx and the graphical technique
for fitting an aquifer We, determine the strength of the aquifer. Assume
aquifer(water+void) is a weak function of pressure and is 1*10-6
psi-1
at 2925 psia,
1.8*10-6
psi-1
at 2525 psia and 3.8*10-6
psi-1
at 2125 psia. This increase in
compressibility is basically to account for the fact that the pores in the aquifer are
losing water that is an incompressible fluid and air occupies the voids. What is the
initial gas in place predicted by the material balance calculation? How does this
compare with the gas in place from the earlier volumetric calculations? Comment
Question 3
A well produces 45.3 bbl of condensate and 742 MSCF of sales gas daily. The condensate
has a molecular weight of 121.2 and a gravity of 52.0 oAPI at 60oF.
a. What is the gas-oil ratio on a dry gas basis?
b. What is the liquid content expressed in barrels per million standard cubic feet
on a dry gas basis?
c. What is the liquid content expressed in GPM on a dry gas basis?
d. Repeat parts (a), (b) and (c) expressing the figures on a wet or gross gas basis.
Question 4
The initial daily production from a gas-condensate reservoir is 186 STB of
condensate, 3750M SCF of high-pressure gas and 95 M SCF of stock tank gas. The tank
oil has a gravity of 51.2 oAPI at 60oF. The specific gravity of the separator gas is 0.712
and of the stock tank gas, 1.30. The initial reservoir pressure is 3480 psia, and the
reservoir temperature is 220oF. Average hydrocarbon porosity is 17.2% and connate
water saturation is 0.2. Assume standard conditions of 14.7 psia and 60oF.
a. What is the average gravity of the produced gases?
b. What is the initial gas-oil ratio?
c. Estimate the molecular weight of the condensate.
d. Calculate the specific gravity (air = 1.00) of the total well production.
e. Calculate the gas deviation factor of the initial reservoir fluid (vapor) at
initial reservoir pressure.
f. Calculate the initial moles in place per acre-foot.
g. Calculate the mole fraction that is gas in the initial reservoir fluid.
h. Calculate the initial (sales) gas and condensate in place per acre-foot

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