1 ABSTRACT The main objective of this experiment is to measure the fluid saturation of rock sample by using the Dean-Stark extraction method. The rock sample is saturated with 100% water. Then, a solvent, usually toluene is dripped into the flask for heating, over the sample. In this method, the toluene is vaporized and vapor flows through the rock sample; allowing the saturated water to vaporized and recondensed in a cooled tube in the top of the apparatus and the water is collected in a calibrated chamber. By applying the formula, fluid saturation can be determined. In comparison with other methods such as retort method, Dean-Stark extraction method is the best method compared to the retort method in terms of accuracy. Besides that, the rock sample can be reused for further experiment. In conclusion, the Dean-Stark extraction method provides a direct determination of fluid saturation. However, due to lack of experimental data, the actual results cannot be analyzed.
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1
ABSTRACT
The main objective of this experiment is to measure the fluid saturation of rock sample by
using the Dean-Stark extraction method. The rock sample is saturated with 100% water. Then, a
solvent, usually toluene is dripped into the flask for heating, over the sample. In this method, the
toluene is vaporized and vapor flows through the rock sample; allowing the saturated water to
vaporized and recondensed in a cooled tube in the top of the apparatus and the water is collected
in a calibrated chamber. By applying the formula, fluid saturation can be determined. In
comparison with other methods such as retort method, Dean-Stark extraction method is the best
method compared to the retort method in terms of accuracy. Besides that, the rock sample can be
reused for further experiment. In conclusion, the Dean-Stark extraction method provides a direct
determination of fluid saturation. However, due to lack of experimental data, the actual results
cannot be analyzed.
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INTRODUCTION
A reservoir depends on its critical parameters to produce economically and efficiently. Two of the
parameters are porosity, which can be defined as the measurement of the rock’s ability to hold a
fluid, and permeability, which defines the characteristics of the rock that allows a fluid to flow
through the rock. In this experiment, the final critical parameter is the fluid saturation. Fluid
saturation can be defined as the measurement of the void spaces in the rock that are occupied by
fluids such as gas, oil and water.
In other words, fluid saturation can be identified as the ratio of the total volume of the fluid
to the void spaces volume of the rock. Generally, the critical parameter can be expressed
mathematically by the following relationship:
Fluid Saturation = Total Volume of the fluid
Void spaces volume
Figure 1: Fluid saturation relationship
By applying the above relationship to each reservoir fluids (e.g. gas, oil and water), the
relationships gives the following equations where Sg is the gas saturation, So is the oil saturation
and Sw is the water saturation. The saturation of each reservoir fluid ranges between 0 to 100 %.
By definition, the summation of all the fluid saturations equal to 1.
Sg = Vg
Vp
So = Vo
Vp Sg + So + Sw = 1
Sw = Vw
Vp
Figure 2: Fluid saturation of each fluid
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The amount and availability of each of fluids (gas, oil and water) depend upon gravity and
external hydrodynamic forces such as interfacial or surface tension forces that occur between the
fluids or between the fluids and the rock. Surface tension forces can be described as the forces
acting on the interface while interfacial forces are the one that acting on the same fluids. E.g.
liquid-vapor form. The interfacial forces can be distinguished into various forms such as liquid-
vapor, liquid-liquid, and fluid-liquid forms.
Interfacial/surface tension forces Explanations
Liquid-vapor This force results from the differences of molecular
attractions of gas and liquid molecules
Liquid-liquid This force results from the differences of molecular
attractions of different liquids
Fluid-solid This force results from the preference for the fluid
molecule to be attracted to the solid surface
Table 1: Explanations on interfacial/surface tension forces
The interfacial forces are important to as it gives rise to what known as a capillary pressure.
Capillary pressure is the difference in pressure across the interface between two immiscible fluids.
These fluids can be differentiated into wetting phase and non-wetting phase. For examples, in oil-
water system, the water is the wetting phase while in oil-gas system, the oil is the wetting phase.
The capillary pressure is significant to the fluid saturations. These two parameters can be relate to
each other. For instance, at decreasing water saturation, the capillary pressure increases.
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AIM/ OBJECTIVE
To determine the fluid saturation of a rock sample using retort method
THEORY
The fluid saturation is defined as the ratio of the volume of fluid in a given core sample to the pore
volume of the sample:
Sw = 𝑉𝑤
𝑉𝑝 S0 =
𝑉𝑜
𝑉𝑝 Sg =
𝑉𝑔
𝑉𝑝 (Eqn. 1)
Sw + So + Sg = 1
(Eqn. 2)
Where;
So – Oil saturation Vo – Oil Pore volume
Sg – Gas saturation Vg – Gas pore volume
Sw – Water saturation Vp – Pore volume
Vw – Water pore volume
Fluid saturation can be define either as a fraction of total porosity or as a fraction of
effective porosity. The fluid in void space are not interconnected cannot be produced from a well,
therefore the saturations will be more significant if expressed on the basis of effective porosity.
The weight of water collected from the sample is calculated from the volume of water by the
relationship:
Ww =ρw x Vw (Eqn. -3)
Where;
Ww – weight of water
ρw – water density in g/cm3.
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Oil volume can be calculated as Wo /ρw which is the weight of oil removed from the core and can
be measured by equation below;
Wo = WL – Ww (Eqn. 4)
Where;
Wo – Weight of oil
WL – Weigh of liquid
WL is the weight of liquids removed from the core sample in gram (g). The weight of liquid can
be determined using equation below;
WL = WSat - Wdry
Where;
Wsat – Weight of original saturated sample
Wdry – Weight of desaturated and dry sample
Pore volume Vp is determined by a porosity measurement and bulk volume;
Vp = ф Vb
Where;
Ф – Porosity
Vb – Bulk volume
Bulk volume can be measured by equation below:
Vb = π (D/2)2 L
Where D and L are diameter and length of the core sample, respectively.
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Oil and water saturation may be calculated by Eqn. 1 and gas saturation can be determined using
Eqn. 2.
APPARATUS AND MATERIALS
Apparatus
1. Dean–Stark Apparatus
2. Heating Plate
3. Desiccater
4. Weighing balance
Materials
1. Cylindrical rock sample
2. Thimble
3. Water
4. Toluene
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PROCEDURES
1. A 100% water-saturated rock sample was prepared.
2. A clean and dry thimble was prepared n weighted. Tongs was used to handle the thimble.
3. A cylindrical rock sample was placed inside the thimble, then quickly weigh the thimble
and sample.
4. The extraction flask was filled with two-thirds full with toluene.
5. The thimble with the sample was placed into the long neck flask.
6. The heating plate was turn on and the rate of boiling is adjust so that the reflux from the
condenser is a few drops of solvent per second.
Note: The water circulation rate should be adjusted so that excessive cooling does not
prevent the condenser solvent from reaching the core sample.
7. The volume of collected water in the graduated tube was measured.
8. After the process is complete, place the rock sample was placed into the oven (from 105°C
to 120°C).
9. The dried sample was stored in a desiccater.
10. The weight of the thimble and the dry sample was measured.
11. The loss in weight WL of the core sample due to the removal of oil and water was measured.
12. The density of a separate sample of the oil was measured.
13. The pore volume Vp of the sample was determined.
14. The oil, water and gas saturations was calculated.
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RESULTS
Volume of sample, Vb = 8 cm3
Porosity of rock sample , ø = 0.080
Lose in weight due to removal of oil and water , WL = 0.494 g