This document describes an experiment to measure the capillary suction time (CST) of a bentonite mud sample. The CST test measures how quickly water passes through a filter medium and indicates the filterability and permeability of drilling muds. The experiment involves mixing water and bentonite to make a mud sample, calibrating a mud balance, filling the balance cup with the mud and measuring its density, diluting a portion of the mud with water, and using the mud balance to measure the CST. The CST test is commonly used in the petroleum industry to evaluate borehole stabilization, study shale properties around the wellbore, and analyze the effects of salts and polymers on drill cuttings.

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Petroleum department
3rd stage
Group (A)
Drilling Lab
10th
Experiment:
Capillary Suction Time
Date of experiment: May 12th
2016
Supervised by:
Mr. Sarhad A. Farkha
Prepared by:
Muhammad Faisal

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Aim of experiment:
The capillary suction time (CST) test is a commonly used method
to measure the filterability and the easiness of removing liquid base
from drilling fluid, slurry and sludge in numerous environmental and
industrial applications.

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Theory:
A type of static filtration test for water-base drilling fluid that
measures the filtration rate (time for free water to pass between two
electrodes) using filter paper as the medium. It is used primarily to
indicate filter-cake permeability, but data from the test have been
used to study how clays and shales react in filter cakes and how
brines of various types affect clays in a filter cake.

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Introduction:
The Capillary Suction Time (CST) Test has been used since the
1970's as a fast, yet reliable, method for characterizing fluid
filterability and the condition of colloidal materials in water treatment
facilities and drilling fluids. For the latter, it has usually been applied
to determine the state of flocculation of clay-bearing fluids and to
screen potential shale inhibitors.
The Capillary Suction Time device measures the relative flow
capacity of a slurry of ground formation rock used to form an artificial
core and it is an indication of clay swelling. A rock sample with
dispersible or swelling clays would have a lower pseudo permeability
and will have a longer CST time while the one without clay or other
fine particles would have a shorter retention time.

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Apparatus & materials:
Mud balance Electronic
balance Beaker
Syringe Electric mixer & steel vessels

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Water Bentonite
Calibration:
1. Remove the lid from the cup.
2. Fill the cup with fresh water around 70°F (21°C).
3. Put the lid back on the cup, (water should come out from the
lids hole).
4. Set the rider on 8.3 ppg or 1
specific gravity.
5. Add or remove steel shot
from the Shotwell until the
instrument is in balance and
the bubble in the level rests in
the center of the level glass.

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Procedures:
1. Weigh 25.05 gm of bentonite on the electric balance.
2. Pour 489.97 cc of water into a 500 ml beaker.
3. Pour the water into two vessels and stir the water with the mixer.
4. Slowly add the bentonite to the stirring water.
5. Leave the mixer running for few minutes till we have a good
mixed mud.
6. Mix the mud in one of the vessels with the mud in the other.
7. Place the mud balance base (preferably in carrying case) on a
flat level surface.
8. Fill the clean, dry cup to the top with the freshly obtained mud
sample to be weighted.
9. Place the lid on the cup and set it with a gentle twisting motion.
Be sure that some mud is expelled through the hole in the cap

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as this will ensure the cup is full and also will free any trapped
air or gas.
10. Cover the hole in the lid with a finger and wash all mud from
outside of the cup and arm. Then thoroughly dry the entire
balance.
11. Place the balance on the knife edge and move the rider
along the outside of the arm and leave it on 8.58 ppg (the
expected mud density) and wait till the cup and arm are
balanced as indicated by the bubble.
12. Obtain 325 cc of water by the beaker and syringe.
13. Mix the water with 300 cc of the mud that we prepared
previously, by using the electric mixer again.
14. Pour the diluted mud into the mud balance cup, then place
the lid on the top (some mud should expelled from the lids hole.
15. Put the rider on 8.45 ppg and observe the level bubble till it
settles in the center.
16. Clean and dry the mud balance when finished.
Discussion:
Q1) what are the applications of CST in petroleum industry?
A1)
 Borehole stabilization to determine the best electrolyte and
polymer to use for maximum shale swelling inhibition.
 Evaluating colloidal shale properties to study the reduction of
permeability of the formation around the wellbore.
 Evaluating the effects of soluble salts and polymers on
cuttings.
References:

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Azar, J. J. & Samuel, R., 2007. Drilling Engineering. Tulsa, Oklaoma:
PennWell Corporation.
Committee, A. S. S., 2011. Drilling Fluids Processing Handbook.
s.l.:Elsevier.
Mian, M. A., 1992. Petroleum Engineering Handbook for the
Practicing Engineer. Tulsa(Oklahoma): PennWell Books.