BAKER HUGHES - Drilling Fluids Reference Manual

BOREHOLE PROBLEMS
Grogan Technique
Accurate placement of spotting fluid is difficult when hole enlargement has occurred and the
spotting fluid must be placed some distance above the drill collars. Grogan outlined one
technique for spotting a fluid which is lighter than the drilling fluid in use. This procedure utilizes
the casing pressure observed after displacing spotting fluid from the drillstring and the relative
gradients of drilling fluid and spotting fluid. For example, a casing pressure of 200 psi is noted
after displacing a 6.8 lb m /gal spotting fluid into the annulus containing 10.8 lb m /gal drilling fluid.
Calculated length of column of spotting fluid would initially be equivalent to observed casing
pressure divided by fluid gradient, less spotting fluid gradient.
Subsequently after pumping drilling fluid equivalent to volume of spotting fluid, a casing
pressure of 150 psi is observed, which would indicate that the column length is 721 feet [150 lb /
(.562 – .354) = 721 ft] and that the top of column is 1682 feet off bottom. This procedure can be
continued until placement of spotting fluid is achieved. When spotting fluid density equals
drilling fluid density, this technique will not apply and it will be necessary to use more than the
calculated volume to compensate for error caused by hole enlargement.
Remedial Procedures Using Spotting Fluids
If the drillpipe becomes stuck, it must first be determined where the pipe is stuck. This may be
accomplished by the following practices.
• Stretch Indication – The drillpipe is pulled into tension with the amount of stretch and force
required to stretch the pipe recorded. Then, a calculation can be made which will give an
approximation as to where the pipe is stuck. This is not an accurate test especially in a deviated
hole as it may give false results.
• Freepoint Indicator Tool – An electric wireline tool called a freepoint tool is run inside the
drillpipe on wireline. The pipe is worked up and down and torqued up as the tool is run down
the hole. When the tool no longer indicates pipe movement, the point of differential sticking
has been located. This is the most accurate means of determining exactly where the drillstring
is stuck.
One method of freeing stuck pipe is to spot oil/synthetic which contains a surfactant. MIL-
FREE ® is used only as an un-weighted spotting fluid in water-base fluids. Approximately 2
gallons of MIL-FREE is added to each barrel of oil/synthetic that is required to cover the zone of
stuck pipe.
Recommended Treatment (BLACK MAGIC SFT)
For 100 bbl of prepared BLACK MAGIC ® SFT, thoroughly mix the following amounts of
materials, shown in Table 7-8, to obtain the desired fluid weights.
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006 7-37