BAKER HUGHES - Drilling Fluids Reference Manual

Water Based Drilling Fluids
lumps and so provide efficient use of these polymers, and optimum extension of the clay.
Mixing clay extenders in a five gallon bucket with a nail hole in the bottom for dripping
the clay extender into the flowline will work as a “poor-boy” method, but leaves a lot to
be desired for proper metering of the product into the active system.
Brackish Water and Seawater
Brackish water and seawater are often used as make-up water for spud fluids on inland barge and
offshore drilling operations. The sodium chloride content generally ranges from 10,000 to 35,000
mg/L. Hardness ranges from 300 to 1300 mg/L depending upon proximity to river drainage.
Although hardness may be reduced to an acceptable level by adjusting the pH to 10.5 with caustic
soda, the chloride content cannot be treated out economically, thus it remains as a contaminant
which suppresses the yield of bentonite. Therefore, bentonite should be pre-hydrated in fresh
water, or other viscosifiers such as SALT WATER GEL should be considered if this water is to
be used.
SALT WATER GEL (attapulgite) is an effective viscosifier in a sodium chloride environment.
Normally, 20 lbm/bbl (with good shear) is sufficient to obtain sufficient hole cleaning on surface.
Pre-hydrated bentonite can provide additional viscosity and will also improve the quality of the
filter cake. However, if facilities are not available for pre-hydration the addition of 5 to 6 lbm/bbl
of MILGEL directly to the system improves cake characteristics to some extent. Attapulgite is not
allowed in many parts of the world due to working environment concerns related to lung disease.
A proper respirator or breathing filter mask must be used while mixing SALT WATER GEL as a
safety measure. When the clay is in the wet state no potential working environment risks exist.
GUAR GUM (2 to 4 lbm/bbl) is a cost-effective viscosifier in seawater and is commonly used in
offshore environments, especially where drill water (freshwater) supplies may be limited. GUAR
GUM viscosity decreases with increased temperature and has a temperature limit of
approximately 150°F. GUAR GUM is typically used for viscous pills. GUAR GUM fluid should
not be stored in the pits for greater than 24 hours due to the possibility of bacterial degradation. It
is recommended that a bactericide/biocide be used to prevent degradation.
Seawater is often used for fluid make-up and maintenance on inland barge and offshore drilling
operations, primarily because of its availability and inhibitive characteristics.
The ionic composition of typical seawater is noted below.
Reference Manual
Baker Hughes Drilling Fluids
3-32 Revised 2006