BAKER HUGHES - Drilling Fluids Reference Manual

Water Based Drilling Fluids
• Bleed-off lines for air line and drillpipe.
• String float in drill pipe.
• Large disposal pit for retention of foam and slurry.
• Butane or propane flare at blooie line for detection of gas.
• Bath device for applying corrosion inhibitors to drill pipe.
The primary objection to stiff foam drilling is that the foam must be discarded as it comes from
the well. A satisfactory chemical or physical method of de-foaming the system has not been
found. The cost of new slurry volume is minimized, however, by the fact that relatively lowslurry
volumes can be circulated with good hole cleaning. Slurry injection rates may vary from
12 to 30 gal/min depending on hole size. Twenty (20) gal/min would be typical for a 9 5 / 8 inch
hole.
Stiff foam densities as low as 4 lbm/gal measured at the flow line can be maintained. This not
only results in reduced lost circulation, but provides a fluid which permits good penetration rates.
Use of a stiff foam system is quite effective to depths of around 6000 feet. Below this depth,
compressibility of the foam by the hydrostatic head is such that little reduction in density is
obtained. Maintaining back pressure on the well enables a higher air/fluid ratio and, thus,
reduced fluid density, but the operation is more complicated and has not been used extensively.
Potassium-Base Fluids
The use of potassium as a Base Exchange ion to stabilize drilled shales has been accepted by
many operators in various geographic areas worldwide. Its use in the Gulf of Mexico has been
greatly restricted due to the toxic affect of potassium on the test species, Mysidopsis Bahia
shrimp. Potassium is widely used internationally, and comes from many sources, including;
potassium chloride, potassium carbonate, potassium acetate, and potassium hydroxide.
The major applications for potassium systems are,
• Drilling soft gumbo (high water content reactive clay structure with elevated cation
exchange capacity) formations to prevent bit balling, clay swelling, clay hydration and tight
hole problems that are commonly associated with drilling reactive formations.
• Drilling indurate shales such as those in the foothills of Canada and West Texas where
excessive sloughing and borehole enlargement are common problems. This is not to
mistaken for tectonically stressed formations.
• Drill-in or workover fluids where the pay zone contains water sensitive clays intermixed
with the producing formation.
• Functioning as the first line of defense for all dispersible drill solids, i.e. preventative
pretreatment chemistry for dispersible clay, thus enhancing solids control efficiency.
Potassium is an effective clay swelling/hydration inhibitor, where the concentration of potassium
to achieve the desired result is often a function of the shale being drilled. There are many areas in
the world where successful potassium applications have been documented; however there are
other areas such, as in the kaolinitic shales of northern South America, where failures are also
well documented. The use of potassium in kaolinitic shales is strongly discouraged due to the
destabilizing affect of the potassium ion on kaolinite.
To accomplish maximum inhibition with potassium, it must be the intervening ion within the
fluid phase of the drilling fluid. As an example, it would require a minimum of 18 lbm/bbl of
Reference Manual
Baker Hughes Drilling Fluids
3-48 Revised 2006