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```									Energy, Climate & Water in the 21st Century                                    Dr. Paul Bommer
TXESS Revolution Summer Institute                   Dept. of Petroleum & Geosystems Engineering

Drilling Mud Density and Viscosity

Purpose: This lab will allow the student to practice using –
(1) The mud balance to determine the density of drilling fluid.
(2) The plastic viscosity of the mud.

Exercise Supplies and Equipment:

(1) A Hamilton Beech Mixer
(2) A mud balance.
(3) A Fann 35 Rheometer

Mix the 17.5 g of bentonite clay in 350 mL (g) of tap water for ten minutes using the
Hamilton Beech mixer. Use the electronic scale to weigh the correct amount of water and
clay. Add the clay to the water using a paper funnel.

Notes on mixing: one barrel of fresh water weighs 350 pounds and 350 mL of fresh water
weighs 350 grams. In the lab, 350 mL of fresh water is equivalent to 1 barrel of fresh
water. Therefore, the addition of one gram of an additive to 350 mL of fresh water is

Remarks on Density:

Mud weight provides pressure in the well that will be larger than the pressure in the
reservoirs. This creates a pressure gradient from the well bore into the reservoirs that
have been drilled. If the pressure is larger in the well bore than in the surrounding
reservoirs, flow cannot occur from the reservoir into the well. This is the primary
mechanism that prevents blow outs. The pressure in the well can be computed using:
pWB  0.052  D
 lb 
pWB  pressure in the well bore  f2 
 in 
 lb 
  drilling mud density  m 
 gal 
D  depth  ft 
62.4 lb m ft 2 32.2 ft lb f sec 2 1 gal
0.052  pressure gradient to density ratio for fresh water =
144 ft 3 in 2 32.2 sec 2 lb m ft 8.33 lb m
The density can be measure in the mud balance. Be sure to calibrate your balance using
fresh water first.

The density can also be calculated using the amounts mixed and the density of the
components. Water density = 1.0 g/mL and the clay density = 2.6 g/mL.

Drilling Mud Density and Filtration Rate                                                     1
Energy, Climate & Water in the 21st Century                                    Dr. Paul Bommer
TXESS Revolution Summer Institute                   Dept. of Petroleum & Geosystems Engineering

Density Exercise:

Drilling Mud Density:

First calibrate the balance by measuring the density of tap water as shown below.
The density should be 8.33 Lbm/gal. If there is any difference between the scale reading
and the true value, record the difference and use this as a correction for the mud density
determined using this balance.

(1) Hold the mud cup of the mud balance over the sink and fill it to over flowing.
(2) Place the cap on the top and spin it to make sure it is seated and the extra mud has
been expelled out the top of the cap.
(3) Place your finger over the hole in the cap and rinse off exterior mud in the sink.
(4) Carefully dry the outside of the cup and place on the balance stand.
(5) Slide the weight on the beam until the bubble is centered in the sight glass on the
beam.
(6) Read and record the mud density off of the top scale in lb/gal.
(7) Place the mud back in the sample container and wash the mud cup and cap in the sink.

Measured Water Density = ________ ppg
Balance correction = _________ ppg

Repeat this procedure for the mud that you mixed.

Remarks on Viscosity:

Viscosity is generally considered the resistance of a fluid to flow. The larger the
viscosity, the higher the pump pressure will be to pump a given flow rate through a given
circulating system. Viscosity is reported in centipoises (cp) in U.S. units and pascal-
seconds (Pa-sec) in S.I. units.

After you have measured and recorded the density of the mud use the Fann 35
rheomoeter to measure the viscosity of water and of the mud you mixed.

Viscosity Exercise:

(1) Fill the rheometer cup with mud up to the line inside the cup.
(2) Place the cup on the rheometer table and raise the cup until the line on the
rheometer cylinder matches the mud level in the cup.
(3) Turn on the rheometer and record the torque reading (degrees) at 600 rpm and at
300 rpm.
(4) Record this on the data page.
(5) The plastic viscosity in centipoises (cp) is the difference between the 600 and 300
Do this for water and for the mud you mixed. Be sure to clean the rheometer after the
mud.

Drilling Mud Density and Filtration Rate                                                     2
Energy, Climate & Water in the 21st Century                                     Dr. Paul Bommer
TXESS Revolution Summer Institute                    Dept. of Petroleum & Geosystems Engineering

Data and Calculations:

Fluid                    Water             Mud
Corrected Density (ppg)
Calculated Density (ppg)

600 rpm rheometer deg
300 rpm rheometer deg
viscosity (cp)

If the well is 6,000 ft deep, what is the pressure at the bottom of the well due to the
hydrostatic pressure of the mud? _________ psi

If pump pressure in turbulent flow is proportional to viscosity raised to the 0.25 power,
what is the multiplier for pump pressure when pumping the mud? _______

Drilling Mud Density and Filtration Rate                                                      3

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