CONTROL OF MUD WEIGHT

EFFECT OF ADDING BENTONITE ON MUD PROPERTIES FOR FRESH AND SALT WATER BASE MUD:

Procedure

1. Add to every 400 c.c batch of fresh water base mud 2, 4, 6 and 8 grams of bentonite and stir for 10 minutes.
2. Measure the density lb/gal, viscosity c.c. (apparent and plastic) and yield
   point lb/100 ft, using the Rheometer for every batch.
3. Add 20.6 ml of 10% by weight salt water to every batch. Stir for 5
   minutes and repeat step (2).
4. Report all the results (density, viscosities, yield) for every batch in a convenient table. Plot them versus the amount of bentonite in gram in two plots, one for fresh water and the other for salt water.

Include the following points in your discussions:

• Discuss the effect of adding bentonite on density.
• Discuss the effect of adding bentonite on the rheological properties.
• Correlate and justify the results obtained for fresh and salt water.
• What is the effect on yield point?

EFFECT OF ADDING WEIGHT MATERIAL (BARITE):

Theory

Barite was first used, in California, in a well being re-drilled with cable tools in 1923. According to that case, density of the mud was raised to 90 lb/ft3 (1.44 gr/cm³ to control gas in flow and to stop caving.

One function of barite has developed – the preparation of a temporary high density plug formed from slurry of a barite in water (2.65 SG). Such slurry contains the maximum concentration of barite that is used – about 750 lb/bbl (2100 kg/cm³). The minimum concentration of barite might be as low as 10 lb/bbl (28 kg/m³), although usually it would be substantially higher.

The quantity of barite required to raise the density of a given volume of mud a specific amount can be readily calculated from the relation, in consistent units:

where
Ρ^f= Final Mud Density
Ρ^o= Original Mud Density
Ρ^B= Barite Density = 35.82 ppg
V^o= Original Mud Volume
V^B= Barite Volume
Wt^B= Barite Weight
NB: Specific Gravity of Barite = 4.3

Test Procedure

1. Calculate and list the amount of barite required to increase the density of
   each batch from 8.6 ppg to 9, 10, 11 and 12 ppg.
2. Obtain 400 cc of original base mud (density 8.6)
3. Add the calculated amount of barite to each batch, stir for about 2
   minutes and measure the Apparent and Plastic Viscosities and Yield
   Point.
4. Repeat step 3 for Salt water-base mud.
5. Tabulate the results and plot the density (ppg ), viscosity (apparent and
   plastic) and yield point versus the amount of barite added.

WATER-BACK (ADDING WATER TO A CHEMICALLY TREATED MUD)

1. Obtain a 350 c.c. of water base mud of 13.5 ppg weight and 9.5 pH.
2. Add water incrementally and measure the Mud weight every time to
   reach 10.5 ppg and same (9.5) pH.
3. Measure the viscosity and gel-strength and check if any change occurred.
4. List your results in an appropriate table.