1. The experiment aims to clean core plugs obtained from a reservoir of hydrocarbons using a Soxhlet extraction apparatus to extract oil and calculate porosity. 2. A Soxhlet extraction involves boiling toluene in a flask, with its vapors condensing and extracting oil from the core plugs in a thimble. The process repeats through cycles of filling, soaking, and draining until the solvent runs clear. 3. The experiment involves placing core plugs in a thimble, extracting with toluene for a minimum of 7 cycles or until the plugs are clean, then drying and weighing the plugs to calculate effective porosity after hydrocarbon removal.

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Petroleum department
3rd stage
Group (A4)
Reservoir Lab
2nd
Experiment:
Core Cleaning
Date of experiment: December 10th
2015
Supervised by:
Mr. Haval Hawez
Prepared by:
Muhammad Faisal

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Aim of experiment:
The main objective of this experiment is to clean the obtained
core plug from hydrocarbons and to calculate the porosity of the
core.

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Theory:
A Soxhlet extraction apparatus is the most common method for
cleaning sample, and is routinely used by most laboratories. A
toluene is brought to a slow boil in a Pyrex flask, its vapors move
upwards and the core becomes engulfed in the toluene vapors (at
approximately 110℃). Eventual water within the core sample in the
thimble will be vaporized. The toluene and water vapors enter the
inner chamber of the condenser, the cold water circulating about the
inner chamber condenses both vapors to immiscible liquids.
Recondensed toluene together with liquid water falls from the base
of the condenser onto the core sample in the thimble; the toluene
soaks the core sample and dissolves any oil with which it come into
contact. When the liquid level within the Soxhlet tube reaches the
top of the siphon tube arrangement, the liquids within the Soxhlet
tube are automatically emptied by a siphon effect and flow into the
boiling flask. The toluene is then ready to start another cycle.A
complete extraction may take several days to several weeks in the
case of low API gravity crude or presence of heavy residual
hydrocarbon deposit within the core. Low permeability rock may also
require a long extraction time.

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Introduction:
The Soxhlet extractor (Soxhlet, 1879) was originally designed for the
extraction of a lipid from a solid material but is used extensively in
core analysis to remove water and oil from core samples. A schematic
of a Soxhlet extractor assembly is shown in Fig 1. The principal
components are:
 A round bottomed flask or extraction pot (2) filled with solvent
 A stirrer bar or anti-bumping granules (1)
 A side arm (3)
 A Soxhlet thimble containing the core samples (5)
 A siphon arm inlet (6) and outlet (7)
 A reduction adaptor (8)
 A condenser unit which can be
circulated with chilled water via
ports 9 and 10
The plugs are placed in the soxhlet
thimble which is fitted with a reflux
(siphon) tube (6 and 7). The round-
bottomed flask (2) sits on a heating
mantle and is part filled with solvent.
In most applications, this will be
toluene initially. The heating mantle is
switched on. When the solvent

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reaches its boiling point it evaporates. The solvent vapor travels up
the side arm (3), bypassing the sample chamber itself, to the
condenser (9) which is continually circulated with chilled or cold
water. The solvent vapor condenses and falls down into the soxhlet
thimble containing the plugs. As the hot solvent fills the chamber, it
diffuses into the pores of the core and leaches oil. As the temperature
of toluene in the chamber is around 100 °C or greater. It causes water
from the core to evaporate. The distilled solvent slowly fills the
sample chamber, eventually submerging the core samples. When the
level of solvent reaches the siphon point (6) the solvent and oil
(colored green) siphon or reflux from the thimble (via the syphon arm
outlet (7)) into the bottom flask exposing the core plugs in the
chamber. The bottom flask will now contain solvent and oil extracted
from the core. As the oil solvent mixture that has mimed into the flask
continues to be heated, fresh solvent vapor is produced. Condensed,
falls into the sample chamber, extracts oil, refluxes and the cycle
repeats. This whole cycle is repeated many times (minimum 7 times).
The solvent accumulating in the sample chamber or refluxed into the
flask is regularly checked for discoloration. Nounally, the solvent is
replaced by fresh solvent near the endpoint of cleaning to assess any
further discoloration. In addition, plugs can be removed and checked
under UV light for oil fluorescence. (McPhee, et al., 2015)

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Instruments and devices:
Soxhlet extractor & cold water supply
Laboratory oven

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Test procedures:
1- Remove the sample from the oil and carefully blot dry an excess oil.
2- Place the sample inside the Wathman thimble and quickly weight the sample and
thimble using the analytical balance.
3- Leave the sample in the thimble.
4- Reassemble the apparatus as, tighten the ground joint fitting but don’t apply sealing
or lubricant.
5- Turn on the water supply to begin circulation in the condenser.
6- Turn on the heater and adjust the rate of the boiling so that the reflex from the
condenser is a few drops of solvents (toluene) per second.
7- Allow the extraction to continue for several hours with a minimum of 7 cycles or until
the thimble content dissolved oil stain and is close to original color.
8- Monitor the toluene level during the extraction to ensure that the sample remains
completely submerged in addition.
9- When the extraction is complete the solvent will be clean or water white depending
on the color of oil removed.
10- Read the volume of the water collected in the water trap, if any.
Note: In many cases the sample have been prepared using oil only to saturate the
core sample, therefore the absence of water does not mean an invalid test.
11- Return the thimble containing the sample to the instructor, who will place them in
the drying oven at (105 - 120) degree centigrade.
12- The instructor will advise when to return to collect the dried sample (sometimes will
be the next day).
13- Place the dried sample in desiccators for a few hours prior to weighting to ensure
that they are completely dried.
14- Place the thimble containing the sample in the analytical balance, measure the
weight of the thimble and dried core sample and record the result.
15- Remove the sample and then weight the empty thimble, record the results or note if
there are any grains of the sample remaining in the thimble in the space provide.

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Discussion:
Q1) what is the cold water supply used for in soxhlet extraction
method?
A1) it is used for condensing the toluene vapor.
Q2) why do we need to vaporize the toluene instead of using it
directly as a liquid?
A2) because the toluene flask doesn’t contain clean toluene but
also oil and water from the cleaned cores, that’s why we need to
vaporize the liquid in order to get clean toluene, which changes to
vapor before the other impurities because it is lighter.
Q3) in order to resist high temperatures the flask is made of a
special material. What is it?
A3) the flask is made of heat resisting Pyrex glass.
Q4) is the soxhlet extraction method use for indicating total
porosity or effective porosity.
A4) this method is used to determine the effective porosity because
the toluene can only clean the oil in the interconnected pores.
Q5) explain the cycle’s repetition.
A5) the cycles are repeated when the level of toluene in the siphon
arm reaches the highest point, then when it falls into the flask again
it creates a vacuum and the atmospheric pressure in the thimble
pushes the toluene into the flask again.

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References:
Gluyas, J. & Swarbrick, R., 2013. Petroleum Geoscience. 4th ed.
s.l.:John Wiley & Sons.
McPhee, C., Reed, J. & Zubizarreta, I., 2015. Core Analysis:A Best
Practice Guide. 1sted. s.l.:Elsevier.