The third lab experiment which is Determination of Reservoir Fluid
parameters was done on 17th of October 2017The objective of this
experiment is to determine and relate surface volumes of oil and gas to
reservoir volumes and vice versa, and determine the three parameters using
flash vaporization, differential vaporization and separator test for a
hydrocarbon system including methane, propane, and hexane. The three
parameters are, Gas formation volume factor (Bg), oil formation volume
factor (Bo), and gas solubility (Rsolubility).
The three parameters can be determined by using oil sample on the PVT
simulator and then could predict the quantities of liquid and gas that will
result at surface conditions for one-unit volume of reservoir fluid on the
Theory, Concepts, and Objective of the experiment:
The objective of the experiment was to find the three parameters which
1) Bo =
𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑜𝑖𝑙 𝑖𝑐𝑙𝑢𝑑𝑖𝑛𝑔 𝑑𝑖𝑠𝑠𝑜𝑙𝑣𝑒𝑑 𝑔𝑠 𝑚𝑒𝑠𝑎𝑢𝑟𝑒𝑑 𝑎𝑡 𝑟𝑒𝑠𝑒𝑟𝑣𝑜𝑖𝑟 𝑐𝑜𝑛𝑑𝑖𝑡𝑖𝑜𝑛𝑠
𝑢𝑛𝑖𝑡 𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑜𝑖𝑙 𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑑 𝑎𝑡 𝑠𝑡𝑜𝑐𝑘 𝑡𝑎𝑛𝑘 𝑐𝑜𝑛𝑑𝑖𝑡𝑖𝑜𝑛𝑠
𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑐𝑐𝑢𝑝𝑖𝑒𝑑 𝑏𝑢 𝑛 𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑔𝑎𝑠 @ 𝑟𝑒𝑠𝑒𝑟𝑣𝑜𝑖𝑟 𝑐𝑜𝑛𝑑𝑖𝑡𝑖𝑜𝑛𝑠
𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑐𝑐𝑢𝑝𝑖𝑒𝑑 𝑏𝑢 𝑛 𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑔𝑎𝑠 @ 𝑠𝑡𝑎𝑛𝑑𝑎𝑟𝑑 𝑐𝑜𝑛𝑑𝑖𝑡𝑖𝑜𝑛𝑠
3) Rs= volume of gas measured @ standard conditions associated with a
unit volume of stack tank oil.
To reach the oil-gas separation there are two different methods which
are showed in figure 1 and figure 2 above. Figure 1 show the flash liberation
which is the first method, the gas developed from the oil kept contact with
the oil, and the composition of the system also stayed the same. In addition,
in the figure 2, the differential liberation, the gas extracted was taken away
from the system. The two methods will give different results and the flash
liberation will have less oil volume because of the ejected of the light
hydrocarbons which changes the ratio of heavy to light components to
increasing while the differential liberation increase.
Figure 3# PVT program
The number of the parameters found by using the PVT program in three
steps. First (flash vaporization), the bubble point must have found, and the
pressure should be bigger than the bubbles point. Second (differential
vaporization), reduce the pressure to be smaller than the bubble point and the
gas should be moved to the surface conditions and then it can be measured at
standard conditions. Third, calculate Bo, Bg, and Rs using the data from
second step and the several separator combinations.
The fractional amounts of 0.4, 0.4, 0.2 moles for Hexane, Methane,
and Propane at a temperature of 100 F (38 C) were used with each having a
pressure of 1000 psia were used to start the experiment. The centrifuge’s
liquid and vessel’s gas will be collected through the expansion of the fluid
which will be conducted at cell conditions with a 71.6 F (22 C) temperature
as well as a pressure of 0 psia. The critical button F10 on the keyboard is
used to observe the initial conditions' data. The components of the cell can
be indicated in the right corner to the right. The next step entailed obtaining
the bubble point which is achieved through withdrawal of 1.572cc Hg. Once
the bubble point has been reached, equilibrium must also be attained. This
equilibrium is attained through the combination of the contents of the cells
using the keyboard's F6 key. The key circulates the contents for the mixture
to be obtained.
Performing the expansion of the flash entailed proper combination
inside the cell which was accompanied by the setting the back-pressure
regulator which was adjusted to 1391psia using the keyboard’s F7 button.
The gas vessel was taken out of the vessel using the F8 key a point at which
pressure decline was observed. To maintain a rate of 10 as well as a
maximum of 6cc, the servo pump was used operated through the F3 key.
After this action, the F4 key was used to activate the servo pump, and
observation was made on the flow of the fluid volume inside the cell as the
pressure was being adjusted to 1769psia. Eventually, the servo pump was
stopped due to the high pressure in comparison to the pressure set using the
regulator and evacuation took place. Recording of the gas pressure was done
using the F10 key. The helium supply was fixed to the chromatograph, and
both the gas and the liquid's results analyzed. Additionally, with this data, it
is possible to determine the value of Rsi and Cbf.
The second step entailed the differential liberation which used the
starting conditions established in the previous section although the pressure
in the cell was set to 10cc. Next, the bubble point was identified by adjusting
the cc value to 0.262 cc of Hg and then circulating it using the F6 key on the
keyboard. At this point, all the required data was recorded.
Thirdly, the eight steps of the differential liberation of pressure were
carried out and pressure reduced by 150psia in comparison to the previous
value. For the initial trial, Hg was dropped by 1.22cc, and a drop of it put in
1256psia and at the same time pressure recorded considering it was
1390.2psia. The cell’s cc was 1.688cc and the relevant information recorded.
The back-pressure regulator was adjusted to 1391 psia after reduction of the
gas in the cell. The densitometer D-1 was used to obtain the density of the
opening valve 15. The servo pump was adjusted to 10cc/min using the F3
key and the maximum delivery recorded in figure 4 above. The servo pump
was modified to allow the gas to leave cell using the F4 key. Valve number
thirteen was blocked and the contents circulated using F6 to the point of
equilibrium. To obtain the possible expansion, the eight steps were repeated.
Figure 4*: Differential Liberation.
Results and Calculations:
Pressure Vs. Bo
P Vs. Bg
P Vs. Rs
From the graphs:
- Because of the taken out of the oil from the reservoir, the pressure
decreased until it reached the bubble pt.
- When the pressure reached the bubble pt. the VGas increased, and then
decreased after the bubble pt.
- Vgas rose as the gas developed, VGas factor < 1 the gas in the surface
condition when the pressure is high, when pressure decreased the Voil
Analysis and Discussion:
The experiment was performed in accordance with figures Boil,
Rsolubility, and Bgas. Because the students are prone to mistakes, the precision
might be low and not accurate even after the parameters have been
determined. Additionally, due to the presence of many sources, errors are
also bound to arise unintentionally with the computer being one of the
Additionally, the computer program could shut itself down without
issuing an alert. This will prompt the student to start the experiment from the
beginning and the results obtained earlier might change. The Peng-Robinson
equation in the PVT program simulator could not be accurate. The PVT
program simulator also operates on the basis of several assumptions. These
assumptions are outlined in the following section:
1. It neglects isothermal pressure changes as well as the impacts of the
2. Instantaneous thermodynamic equilibrium.
3. Mercury is assumed not to be compressible.
4. Both the tubing and the volume for the pipes are assumed to be absent
In conclusion, the experiment has managed to attain several objectives
that formed the basis for its carrying out. The overall goal of the experiment
which was figuring the multiple parameters was attained when they were
figured. That is, getting Bgas, Boil, and Rsolubility out as well as connecting the
correlation between the first reservoir and the volume of the surfaces as
shown in the graphs. The separation of the gas-oil can be attained through
two methods, and these are; differential liberation as well as flash liberation.
Moreover, parameters change as the conditions change. Finally, it was
confirmed the amount of liquid and gas that comes out at fluid’s surface
conditions in the reservoir.
*Figure 1, 2, and 4 are from the lab manual.
#Figure 3: from Saturation Pressure of a Binary System Using PVT
Simulator (power point).
- William D. McCain, Jr., The Properties of Petroleum Fluids, 2nd
edition (PennWell Publishing Company, 1990).
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