Sea Water/ Bentonite is a simple mud system for top hole drilling. Viscous bentonite slugs pumped regularly for good hole cleaning. Returns are not be taken to surface during conductor pipe cleaning/ under-reaming; ports in the conductor pipe can be used to minimise the hydrostatic head.

These sections can be successfully and economically drilled with sea water, slugging the hole periodically with 5 to 10 m3 of high viscosity fluid.

The use of flocculated bentonite slugs is recommended to provide the viscosity necessary to ensure that the hole is kept clean throughout these intervals.

If under-reaming is required, prior to running casing, displace the hole with a viscous bentonite slurry, this will ensure that hole fill is reduced and that any tendency for the hole to slough in will be reduced.

Product Functions

• Bentonite (API): Montmorillonite clay for viscosity and fluid loss control.
• Barite: Weighting agent.
• Fluid loss reducing agent.
• Lime: Flocculating agent for high viscosity slugs. Also to be used for pH control together with soda ash.
• Soda ash: To control soluble calcium levels. Also to be used for pH control together with lime.
• Environmentally acceptable biocide.

System Formulation

Sea water/flocculated bentonite slugs:

BENTONITE                               70 kg/m3

LIME                                          2.0 kg/m3

SODA ASH                                0.75  kg/m3

Weighted bentonite/polymer fluid:

BENTONITE                              70 kg/m3

BARITE                                     200 kg/m3

Fluid Loss                                 11 kg/m3

LIME                                         2.0 kg/m3

SODA ASH                               0.75 kg/m3

BIOCIDE                                   0.3 kg/m3

Mixing Procedure

1. Fill the tanks with the required amount of drill water and reduce the total hardness to below 150 mg/l with soda ash. Increase the pH to +/- 9 with a combination of lime and soda ash.

Na2CO3 + Ca(OH)2 = CaCO3 + 2NaOH

A ratio of 106 kg soda ash to 74 kg lime is required for this reaction or approximately 4 sacks of soda ash to every 3 sacks of lime.

2. Add 100 kg/m3 bentonite and allow to hydrate, under maximum shear conditions, for at least six hours.

Just prior to use, dilute with sea water to a bentonite concentration of 60 - 70 kg/m3 and flocculate the fluid by adding 2 kg/m3 lime.

4. For the weighted bentonite/polymer fluid:

(a)     Add the Fluid loss additive @ 5 - 10 mins per sack.

(b)    Add the barite to the required density.