Drilling Practical 1
Drilling Practical 1
Drilling Practical 1
Measurement
Objectives: The objectives for this practical included preparing three different
drilling muds, determining the mud density, specific gravity and hydrostatic
pressure gradient for these water based muds, and comparing the experimental
results with calculated theoretical figures.
Introduction: Formations below the surface of the earth contain fluids which are at
specific pressure values. The mud column exerts hydrostatic pressure, which can
control these formation pressures. Zones with specific pressures require suitable
mud pressures for drilling; in low pressure areas the mud density must be low to
avoid fractures in the formation, while in high pressure areas the drilling mud must
be of relatively high pressure in order to avoid a blowout. For these reasons,
controlling the hydrostatic pressure of a mud column 1 and knowing the specific mud
density are of utmost importance throughout the drilling process.
Apparatus: The following equipment was used throughout this practical:
Mud balance; this included a base, graduated balance arm, cup, lid, knife edge,
rider, level glass and counterweight (See Fig. 1 below).
In addition: electronic mud mixer, electronic balance, plastic spoons and graduated
containers, measuring cylinder, water, bentonite, barite, glass bubbles, polymer,
glass storage containers.
Figure 1: Mud Balance (Image from: Drilling Engineering Practical 1 Online PDF)
Mud 3
Water (94.85%)
Additives (%mass)
Bentonite (5%) Barite (10%)
Bentonite (5%) Glass Bubbles
(10%)
Bentonite (5%) Polymer (0.15%)
1. The necessary amount of water and additives was calculated based on the given
mass percentages, to make up a total of 600 grams of each type of mud. The
required mass was calculated using the formula M = mass percentage x total
mass of mud. The mass components are given in the table below.
Mud
Water
(grams)
Bentonite
(grams)
Barite
(grams)
Polymer
(grams)
Total mud
mass (grams)
60
Glass
Bubbles
(grams)
0
Mud
1
Mud
2
Mud
3
510
30
600
510
30
60
600
569.1
30
0.9
600
2. The required water amount was measured and added to a plastic container.
3. The container was placed under a mud mixer, and fixed accordingly before the
mixer was turned on.
4. The bentonite was slowly added to the container.
5. Slowly, the barite was added to the mud in the container.
6. When the mixture was ensured to be homogeneous, the mud mixer was stopped.
7. The mud was poured into a glass storage container and labelled.
8. This exact process was repeated for the other 2 muds (one with glass bubbles,
one with polymer replacing the barite in step 5).
4. The lid was put back on the cup and rotated for a firm seal. It was made sure that
the vent hole was not covered; some excess mud squeezed out of this hole.
5. Now the hole was covered, and excess mud wiped away using a sponge. The
balance was dried.
6. The cleaned balance was placed into its base with the knife edges firmly in its
fulcrum rest.
7. The rider was adjusted so that the beam was fully balanced, with the spirit level
bubble centred.
8. The mud weight in PPG as well as the specific gravity values were read and
recorded.
9. The mud was poured back into its glass storage container.
10. The process was repeated with the two other muds; cleaning the instrument
between tests- for each sample. After all samples were tested, the balance was
cleaned once more.
Experimental Data and Observations:
Mud
Mud
Mud
Mud
composition data:
1: 510 grams of water, 30 grams of bentonite, and 60 grams of barite.
2: 510 grams of water, 30 grams of bentonite, and 60 grams of glass bubbles.
3: 569.1 grams of water, 30 grams of bentonite, and 0.9 grams of polymer.
=
Mud 1:
=
Mud 2:
=
Mud 3:
510+30+ 60
=9.33 PPG
510
30
60
+
+
1 8.33 2.6 8.33 4.2 8.33
510+30+ 60
=7.36 PPG
510
30
60
+
+
1 8.33 2.6 8.33 0.38 8.33
569.1+30+0.9
=8.60 PPG
569.1
30
0.9
+
+
1 8.33 2.6 8.33 1.6 8.33
Discussion/Further Results:
Looking at the experimental values for mud density and comparing them with the
theoretical values calculated above, we can see relatively high result accuracy. For
mud 1, the observed value of 9.35 pounds per gallon of 9.35 is only 0.02 PPG higher
than the theoretical value of 9.33. For mud 2, the observed value again differs by
0.02 PPG; observed value of 7.34 PPG and a theoretical value of 7.36 PPG. For the
third mud, the accuracy is higher; the observed value matches the theoretical value
(8.60 PPG) at least when calculated to two decimal places.
Overall this suggests the practical was carried out quite accurately, but even so the
effect of systematic error may be seen. One such source of error may have been the
limited accuracy of the measuring equipment; namely the mud balance. Other
sources of error may have been a fault in the mud mixer or an impurity in one or
more of the mud additives.
Mud gradient calculation:
The following formula was used: Mud gradient in psi/ft. = mud weight in PPG x
0.052
Mud 1:
Mud 2:
( 10.2639.33 )
( 35.05
) 2940=3878.761 lb
35.0510.263
Dividing this value by 94, we obtain how many sacks must be added:
9.33
lb
2940 gal=27,430.2 lb
gal
of barite.
27430.2+3878.761=31308.96 lb
31308.96 lb 10.263
of barite total.
lb
=3050.66 gal .
gal