Bentonite based mud may be used to impart stability to boreholes through soft seabed sediments prior to running structural or conductor casing. 30-40ppb bentonite mud shall be used offshore to sweep top hole while drilling and to spot on bottom prior to running surface casing.

Bentonite Pre-hydration

1. Flush tank and lines with drill water.

2. Fill the surface tank to 75 %of capacity with drill water.

3. Check chloride concentration to ensure no sea water contamination. CHECK calcium and magnesium ion concentrations.

4. Add soda ash as required to reduce the calcium content to <200 mg/I.

5. Add caustic soda if necessary to reduce the magnesium content to < 200 mg/I.

6. Add circa 45 ppb bentonite and MIX under maximum shear conditions. USE all available agitators and mud shear guns.

7. Add caustic soda to raise the pH to 10 while adding the bentonite.

8. Allow the bentonite to yield/prehydrate for 4-6 hours prior to use

After the bentonite has hydrated, the preparation procedure shall depend on the intended use of the fluid as follows:

High Viscosity Pills

1. Immediately prior to use, fill the tank with sea water.

2. Add lime to flocculate the fluid if necessary to increase the viscosity.

Note that the increase in viscosity due to flocculation shall be a temporary effect

Use one volume of prehydrated bentonite to one volume of sea water (1:1)

Unweighted Displacement Mud

1. Fill the tank with sea water.

2. Add soda ash and caustic as outlined above.

Weighted Viscous pill

1. Fill the tank with sea water.

2. Add barite till required mud weight is attained.

3. Add soda ash and caustic as outlined above.

Note: In case drill water not available use sea water and salt water gel (35 ppb)