Drilling Fluid Engineering Gel Strength

1. Drilling Lab. Gel Strength
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Koya University
Faculty of Engineering
Petroleum Engineering Department
Third Stage
Drilling Lab.
Gel Strength
Prepared By: Sarwar Salam
Group: B
Experiment Date: Mar. 3rd
2017
Submit in Date: Apr. 06th
2017
Supervised by: Mr.Pshtiwan - Mr.Mohammed
2016-2017

2. Drilling Lab. Gel Strength
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Aim of Experiment:
The aim of this particular experiment is to determine on of
the most important drilling fluid properties under static
conditions; which is the Gel strength.

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Introduction and Theory:
Gel strength is the shear stress of drilling mud that is measured at
low shear rate after the drilling mud is static for a certain period of
time. The gel strength is one of the important drilling fluid
properties because it demonstrates the ability of the drilling mud to
suspend drill solid and weighting material when circulation is
stopped. ( Foundation, Concrete and Earthquake Engineering,2013)
We use the 3-rpm reading which will be recorded after stirring the
drilling fluid at 600 rpm from a rheometer. Normally, the first
reading is noted after the mud is in a static condition for 10 second.
The second reading and the third reading will be 10 minutes and 30
minutes, respectively. You may wonder why we need to record the
3-rpm reading after 30 minutes.
The reason is that the 30 minute-reading will tell us whether the
mud will greatly form the gel during an extensive static period or
not. If the mud has the high gel strength, it will create high pump
pressure in order to break circulation after the mud is static for long
time. Furthermore, increasing in a trend of 30-minute gel strength
indicates a build-up of ultra-fine solid. Therefore, the mud must be
treated by adding chemicals or diluting with fresh base fluid.
In other words, Gel strength is the measurement of the suspension
properties of a drilling fluid. Gel strength is measured with a
rheometer or shearometer and is reported in pounds per 100 square
feet.

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Gel strength is of the upmost importance, especially in coarse-
grained soils (sand, gravel and rock). In a vertical hole, we remove
solids with viscosity and velocity. In HDD, we don’t have velocity
working on our side because of the pumps we use and the size of
reamers we may be using. We can’t depend on annular velocity. In
addition, annular velocity rates that may be desirable in vertical
applications may erode the less consolidated soils that are
encountered at depths as shallow as 3 to 4 feet as are often
encountered in utility HDD. We make the comment that the primary
responsibility of a bit or a reamer is considered to be cutting a bore-
path through the soil, the actual cutting operation.
The secondary responsibility, which is of equal importance, is to
mix the soil that is being cut into aslurry with the fluid. It then
becomes the responsibility of the fluid to suspend these solids and
keep them in suspension until they can be transported out of the
hole. This resulting slurry (solids + fluid) becomes the conveyor belt
to remove at least enough solids to make room for the product line.
It is important to remember that, unlike vertical drilling, there is
never an empty hole. The slurry (solids + fluid) aids in supporting
the ceilings of these horizontal bore-paths. The solids will not
remain in suspension to maintain the slurry without gel strengths.
(Baroid Industrial Drilling products,2016)

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Equipment, Martials and Devices:
The Baroid Rheometer is a coaxial cylindrical rotational
viscometer, used to determine single or multi-point
viscosities. It has fixed speeds of 3 (GEL), 100, 200, 300 and
600 RPM that are switch selectable with the RPM knob.
Additionally, the same switch set to the VAR position
enables speed selection of between 3 and 625 RPM, by
manual adjustment of the variable knob.
(Figure 1) (Baroid Rheometer) (Drilling lab manual,2014)

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Procedure:
1-Preparing a mud of known density (i.e. any drilling
fluid can be used, even if the density was unknown).
2-Stir a sample at 600 RPM for about 15 seconds
3-Turn the RPM knob to the STOP position.
4-Wait the desired rest time (First time 10 seconds).
5-Switch the RPM knob to the GEL position, Record
the maximum deflection of the dial before the Gel
breaks, as the Gel strength in Ib/100ft2
.
6-Repeat 4 and 5 for 10 min Rest time.

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Discussion:
1-Explain the Gel Strength briefly?
 The gel strength is the shear stress measured at low
shear rate after a mud has set for a period of time (10
seconds and 10 minutes in the standard API procedure,
although measurements after 30 minutes or 16 hours
may also be made). The gel strength quantifies the
ability of the fluid to have strength when static, in order
to suspend cuttings, and flow when put under enough
force.
2-What does the Thixotropic property means?
 Thixotropic property means, Property of drilling fluid
for being Semi-solid at static conditions (i.e. when
circulation is stopped) and Liquid when it’s pumped.
3- Why it is necessary for a drilling fluid to have gel
strength property?
 During drilling process we may get faced with
situations that the Circulation process will stop! And as
it is known the mud that‘ve been circulated for a period
of time contains solid particles, cuttings and crushing,
that will gradually (i.e. in high Gelly muds) or instantly

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(i.e. in low gelly muds) deposit and accumulate at the
bottom of the well. Which can cause stuck of drilling
string and drilling bit balling as well.
To avoid such problems, the mud engineer should
carefully control the gel strength of the mud.
4-What factors will affect the Gel strength of drilling
fluid in WBM?
 The following causes will result in the high gel
strength in the water base mud:
Bacteria, Drill solid, Salt, Chemical contamination as lime,
gypsum, cement, and anhydrite, Acid gases as Carbon Dioxide
(CO2), and Hydrogen Sulphide (H2S). (Drilling mud, 2010)
5-What factors will affect the Gel strength of drilling
fluid in OBM?
 For an oil base drilling fluid, there are several points
that will cause the high gel strength in the mud system
as follows:
Over treatment with organic gelling material
Build-up of fine solid particles in the mud (Drilling mud, 2010)
6-Why the student results of test observations was in
a wide range difference?
 When performing the test, there were some noticed
factors which they lead to wide range results of student

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test observations. One of these factors might be errors
and/ Or differences in the previously prepared mud,
another factor can be the error of the reading of test
apparatus reading, because students should have a quick
and accurate sense to measure the reading correctly.
7-Imagine that, during the drilling process you get
circulation stopped, what will be your prior steps?
 At any instant of time if the drilling process got the
stopped circulation either it was expected (i.e. having
prior information that the circulation will stop at
specified time) or non-expected (i.e. sudden situation to
stop circulation, kick or drilling mud loss ,..etc.) the
drilling and mud engineers prior step would be to check
the gel strength of the mud, and if it was at fair level,
then the gel strength additives should be added. To
avoid risk of stacked assembly down-hole.
8-Why the Gel property of the drilling fluid increases
with time?
 The Gel strength is the function of the drilling fluid’s
internal forces which combine particles together to form
semi-solid compound of mud and cuttings. However,
The more the mud gels during shut down periods ,the
more pump pressure will be required to initiate
circulation again.

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References:
1-Foundation, Concrete and Earthquake Engineering (2013) Gel
Strength of Drilling Mud [Online] Available from: http://civil-
engg-world.blogspot.com/2011/05/gel-strength-of-drilling-
mud_08.html [Accessed: Feb.5th
2016].
2- Bariod Industrial Drilling Products (2016) Drilling Fluid
Properties (Horizontal Applications) [Online] Available from:
http://www.baroididp.com/idp/resources/technical-
assistance/publications/tech-papers/fluid-properties-for-
horizontal-applications/horizontal-apps.page?node-id=hm8zxxls
[Accessed:Feb.6th
2016]
3-Cariflex Polyisoprene Products (2013) Wet-Gel Strength
Improvement [Online] Available from:
http://www.kraton.com/products/cariflex/Cariflex%20IR%20lat
ex%20-%20Wet%20Gel%20Strength.pdf [Accessed: Feb. 6th
2016]
4- Drilling-Mud (2010) Gel strength [Online] Available
from: http://www.drilling-mud.org/gel-strength/
[Accessed: Feb. 6th
2016]
5- Jaf,Pshtiwan.T.M., Drilling Engineering Laboratory
Manual,June 2014, Faculty of Engineering,Koya
university