BAKER HUGHES - Drilling Fluids Reference Manual

BOREHOLE PROBLEMS
3. Add correct volume of water (if required) and agitate until thoroughly blended.
4. Add MIL-BAR (or weight material) to the desired density and agitate until thoroughly blended and
smooth.
Note: Weighted spotting fluid at this point should be pumpable yet have sufficient body to
suspend weight material. If spotting fluid is not pumpable, treat lightly with UNI-CAL®.
5. If the chloride concentration of the drilling fluid is greater than 60,000 mg/L, placement of a 25 to 40
bbl freshwater NEW-DRILL ® spacer ahead of the BIO-SPOT as well as behind the BIO-SPOT is
recommended. Spacers are not required if the chloride concentration is less than 60,000 mg/L.
6. Pump spotting fluid at normal pumping rates.
Alternate Methods for Freeing Stuck Pipe
Other methods of freeing stuck drill strings include the following.
Altering Fluid Density
Reducing drilling fluid density may result in freeing stuck pipe. This method would not be
feasible if pressure reduction allowed formation fluids to enter the wellbore. Often it is also time
consuming and expensive.
Drillstem Test Tool
Stuck pipe has also been freed by utilizing a drillstem test (DST) tool above the point of sticking
and releasing pressure below packer. This sudden reduction in pressure may, however, result in
unstable shales falling into the wellbore and an influx of formation fluids from permeable zones.
This technique should be used with extreme caution.
U-Tube Technique
The U-Tube Technique offers the advantage of speed without the inherent cost involved in
reduction of drilling fluid density. Basically, the U-Tube method involves displacing a portion of
the fluid in the upper part of the drillstring with a lighter fluid such as diesel oil or water, then
allowing annulus fluid to flow back on the drillpipe side until equilibrium is obtained. The
hydrostatic pressure reduction desired by lowering fluid level in the annulus can be calculated.
Example
While drilling at 8000 feet, the drillstring stuck while running a survey. Hole size is 8½ inch and
drillpipe is 4½ inch. Casing size is 9 5 / 8 inches and is set at 3000 feet.
Drilling fluid density is 10.6 lb m /gal, and it is desired that hydrostatic pressure be reduced by 250
psi on bottom. Water is to be used to lighten hydrostatic on the drillpipe side.
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006 7-40