Page 183 - Practical Well Planning and Drilling Manual

Section 2 revised 11/00/bc 1/17/01 12:04 PM Page 159

2.3.1
` Directional Planning [ ]

stabilizer will give a dropping tendency to a tangent or build assembly.
Nearbit stabilizers or roller reamers have a box up and box down and
the bit screws directly into the box down. Normally the box up is bored
out so that a float valve can be placed inside. Nearbit stabilizers and
roller reamers at full gauge are used in tangent and build assemblies.
Roller reamers may be used instead of stabilizers in abrasive hole or
if high torque is a problem. In crooked hole country, where spiral holes
can be drilled even with highly stabilized assemblies, the nearbit stabi-
lizer can generate a lot of torque as weight on bit is applied. I experi-
enced this some years ago; we drilled a 12 /4 in hole section with a fully
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stabilized assembly and every time more than about 20 k was applied to
the bit, the rotary table torqued up and stalled out. Back on surface the
nearbit stabilizer and first string stabilizer were worn balloon shaped—
full gauge in the center and up to /4 in undergauge at the top and bot-
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tom edges. This had me extremely puzzled for a while, until I realized
that the only way to wear a stabilizer like that was in a severely spiral
hole. In the same interval on the next well we ran roller reamers in the
first two positions, no torque problems at all and everything came out
full gauge. In this case the final well report (FWR) of the first well made
the recommendation to try the roller reamers on the next well, illus-
trating the central role of the FWR in improving future performance.
Stabilizers come in several flavors. Integral blade types have the
whole tool machined from one block of steel. Sleeve types have
replaceable blades that screw on to a body with a thread machined in
the middle. The sleeve type is more versatile because a stock of blades
can be kept on the rig and changed as necessary, and replacing the
sleeve when it is too worn is much cheaper than replacing an entire
integral blade type. Some people have reported problems with the
sleeve type unscrewing downhole; I have never seen this and I consid-
er that as long as it is properly installed and torqued up (and is not
damaged in some way), unscrewing is very unlikely to occur. To make
and break the sleeve safely a breaker plate should be used; check that
this is available on the rig otherwise tongs will be used that may dam-
age the sleeve and/or the tong.
In an 8 /2 in or smaller hole, integral blade stabilizers should be
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used rather than sleeve types because the flowby area becomes too
small on sleeve stabs.
Stabilizers are also available that allow downhole gauge adjustment.
The first adjustable stabilizer was the Andergauge downhole adjustable

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