BAKER HUGHES - Drilling Fluids Reference Manual

HORIZONTAL AND EXTENDED REACH DRILLING
circumstances. Therefore it is necessary to specify a minimum Yield Stress. The optimum level
required is best established based on field data and experience.
A higher ROP requires a higher flow rate to clean the hole. It is good practice to drill the hole with
a steady ROP and select the required flow rate for hole cleaning accordingly. Before making a
connection, the hole should be circulated at the normal flow rate to clear the cuttings from around
the BHA. Depending upon the hole angle and length of BHA, a circulation time of 5 to 10 minutes
is often required.
Before tripping out, the hole should be circulated at the normal flow rate until the shakers are clean,
and the drill pipe be rotated at maximum speed/reciprocated in the mean time. This may require up
to 3 bottoms-ups, depending on the hole angle and hole size. Below are listed the recommended
number of bottoms-up prior to tripping.
Torque and Drag
Hole Angle, deg 8 ½” 12 ¼” 17 ½”
0 – 10 1.3 1.3 1.5
10 – 30 1.4 1.4 1.7
30 – 60 1.6 1.8 2.5
60+ 1.7 2.0 3.0
Overall friction can become so great in an extended-reach well or horizontal section that the drill
string can only be rotated with great difficulty. Needless to say, this condition is conducive to stuck
pipe. Obviously, this coefficient of friction will be significantly affected by the lubricating
properties of the drilling fluid.
Many of the causes of torque and drag are mechanical, while others are related to hole geometry.
Several, however, can be directly attributed to the drilling fluid. Since wall contact with the drill
string will be extremely high in a horizontal hole, it is imperative that the lubricating characteristics
of the fluid be considered.
Fluid Lubricity
Lubricating qualities of a drilling fluid are normally measured in the laboratory by use of a
lubricity tester. Coefficient of friction between steel wear pieces, or between steel and ceramic
surfaces, is normally determined. Although the coefficient of friction, as measured in these tests,
cannot be applied directly to any particular borehole, it can be used for relative comparisons
between different drilling fluids and/or lubricating additives. A comparison of the coefficients of
friction of several fluid types, as determined by the Baroid lubricity tester, is described in Figure
11-9.
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006. 11-18