Page 199 - Practical Well Planning and Drilling Manual

Section 2 revised 11/00/bc 1/17/01 12:04 PM Page 175

2.3.3
Directional Planning [ ]

there will be little difference between bit and kelly direction due to the
shallow depth. Surveys during kickoff will generally be taken every
single. Jetting can produce very high dogleg severities and must be
monitored as the kickoff progresses.
Since drilling will be fairly fast and the annulus will get loaded up
with cuttings, a float in the string is necessary. Otherwise, you will
have to spend time circulating before every survey to prevent strong
backflow.
Kicking off with a downhole motor. A motor may be configured
with a bent sub above it or it may have a bent housing. Where the
housing bend is close to the bit, the motor may be used in orientated
(sliding) mode or may be rotated while drilling ahead. Such an
arrangement is a steerable system, so called because it can deviate the
well by sliding or drill straight by rotating the drillstring.
If the kickoff is fairly shallow, a UBHO sub can be run above the
motor or bent sub, orientated with the bend. This allows a single shot
survey to be run on wireline with an orientating muleshoe so that the
inclination, azimuth, and toolface azimuth are shown on the survey. By
determining TFA after running the survey, the driller can mark the
drillstring and drill orientated with the drillstring locked in rotation.
Deeper kickoffs call for a measurement while drilling tool is run. This
is due to the time taken to run wireline surveys (and the risk involved
of breaking the wire) and as reactive torque generated at the bit will
have a marked effect on toolface orientation once on bottom with a
longer drillstring. The MWD tool gives a constant readout of inclina-
tion, azimuth, and TFA so that reactive torque can be compensated for.
Whichever system is used (bent sub or bent housing), deviating
the wellbore is achieved by generating a side force at the bit that makes
it cut sideways as well as ahead.
Kicking off on a cement plug (direction not controlled). In a ver-
tical well, it may be necessary to sidetrack around a fish and re-estab-
lish a vertical well to target depth. It is possible to set a cement plug
and kickoff from it with a flexible drilling assembly, as long as the
cement plug has a higher compressive strength than the formation.
Once the cement plug is set, run in with a 60 ft pendulum BHA and
a mill tooth bit. Start to drill on the top of cement, building up to a high
WOB/lower rotary speed. The bottom drill collars should start to buck-
le dynamically, pushing the bit sideways. If the cement plug is harder

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