BAKER HUGHES - Drilling Fluids Reference Manual

Baker Hughes Drilling Fluids
levels. To prevent excessive carbonate levels, it is recommended that a minimum of 100 to 200
mg/L calcium be maintained in the fluid system and the pH be maintained in the 9.0 to 9.5 range.
Treatment and Control Techniques
If excessive carbonates occur in a fluid system and treatment is necessary, the following methods
are recommended. The first method is to treat the system with lime. A sufficient quantity of lime
should be added to increase the pH to at least 9.5 and measurable calcium levels to 100 mg/L. If
noticeable improvement in fluid properties does not occur, continued treatment is necessary.
Treatments of 0.25 to 0.5 lbm/bbl lime may be necessary to reduce carbonates to acceptable
levels. When treating carbonates it is best to make small, incremental additions of the chosen
treatment and observe the results after one complete circulation. Since over-treatment with lime
can be harmful to the NEW-DRILL system, an alternative treatment would be to use a
combination of gypsum and lime. These chemicals should be added simultaneously to raise the
pH and soluble calcium to the levels indicated above. An advantage of using a combination of
gypsum and lime is to buffer the pH increases caused by using lime. A problem can also occur
by over treating with this method as well. Careful monitoring of pH and calcium levels should be
maintained during the treatment phase.
Temperature
Source
As wells are drilled deeper, higher bottom hole temperatures are being encountered. In some
areas with very high geothermal gradients, temperatures may approach 600°F to 700°F at depths
as shallow as 5000 ft. These severe requirements may necessitate designing a special drilling
fluid. Today's drilling fluids are being frequently required to function above 300°F. The NEW-
DRILL system has been used in wells having bottom hole temperatures of 350°F, however, it is
suggested that the PYRO-DRILL or other mud systems specifically developed for geothermal or
high temperature/high pressure (HT-HP) be considered at temperatures above 350° F.
Effects on Fluid Properties
As temperatures rise above 250°F, the degree of flocculation of bentonite starts to increase. This
flocculation can be controlled to some extent with organic thinners but, above 300° to 350°F,
these thinners also begin to degrade and lose their ability to deflocculate the system.
Treatment and Control Techniques
The NEW-DRILL system, because of its low-solid content, is reasonably tolerant to temperatures
up to 300° F. One problem that may occur in a NEW-DRILL system is viscosity reduction at
elevated temperatures. Viscosity may need to be supplemented with a temperature stable
biopolymer such as XAN-PLEX D. If the solids concentration is severe enough to create
viscosity problems from clay flocculation, then deflocculation can be achieved using NEW-THIN
and/or MIL-TEMP (or ALL-TEMP). API filtrate can be controlled with CHEMTROL X.
NEW-DRILL System Benefits
Effects on Torque and Drag
One of the supplemental benefits with the NEW-DRILL systems is related to the low coefficient
of friction of the polymer, coupled with its thixotropic nature and inhibitive qualities. These
factors, in conjunction, have reduced the torque and drag experienced in the field. This has been
particularly evident in directional holes.
Baker Hughes Drilling Fluids
Reference Manual
Revised 2006 3-59