BAKER HUGHES - Drilling Fluids Reference Manual

Water Based Drilling Fluids
on the first trip in a new hole. On rigs equipped with a top drive, it has become routine to pump
out of new hole in stands.
Solids Control
A wide variety of solids control systems have been used with the AQUA-DRILL system. Good
solids control will always be of benefit, but the system has been particularly beneficial when only
average or poor solids control equipment was available. Reduced dispersion of solids and
minimal clay blinding on screens makes the system more flexible than conventional polymer
systems.
MBT Values
A common scenario when drilling reactive clays with conventional polymer fluids is to see a
rapid buildup of gels and MBT requiring rapid dilution to control these properties. In the AQUA-
DRILL system, the problem is often the reverse, i.e., low gels resulting from low MBT values
requiring supplemental additions of XAN-PLEX ® . It is quite normal under these circumstances to
see an MBT value of 15 after 5,000 ft of drilling a 17½" hole through reactive clay formations
with minimal dilution.
Dilution Rates
Experience from past wells has provided the following expected dilution rates. The figures
quoted below are for 4,000 ft of clay with average solids control equipment and fluid weight in
the 11.0 to 13.0 ppg range.
Table 3-23
Clay Type
Mud Weight Selection
Recommended Dilution Rates for AQUA-DRILL Systems
Low Reactivity 0.1 - 0.2 m 3 /m
0.2 - 0.4 bbl/ft
Intermediate 0.15 - 0.3 m 3 /m
0.3 - 0.6 bbl/ft
Highly Reactive 0.25 - 0.5 m 3 /m
0.5 - 1.0 bbl/ft
Hole Size
17½" 12 1/4"
0.05 - 0.15 m 3 /m
0.1 - 0.3 bbl/ft
0.15 - 0.3 m 3 /m
0.3 - 0.4 bbl/ft
0.2 - 0.4 m 3 /m
0.4 - 0.8 bbl/ft
As with any system, poor mud weight selection will mask the benefits of this improved waterbase
fluid. An additional benefit from the improved fluid system can be lost by poor mud weight
selection. In most cases, inadequate weight is the problem. There is no substitute for good offset
data in well planning.
pH Control
The AQUA-DRILL system functions over a wide range of alkalinity values. However, to
minimize clay dispersion, a pH in the range 8.5 to 9.5 is recommended.
Reference Manual
Baker Hughes Drilling Fluids
3-82 Revised 2006