Page 197 - Practical Well Planning and Drilling Manual

Section 2 revised 11/00/bc 1/17/01 12:04 PM Page 173

Directional Planning [ ]
2.3.3

of precession is measured by doing regular drift checks on surface
and while surveying. A drift check simply holds the tool on depth
for 10 to 15 minutes so that several shots are taken. Examination
of these shots will show the rate of precession so that the survey
readings can be corrected for the total drift at the time of the sur-
vey. Laser ring gyros are more accurate than mechanical gyros.

2.3.3. Kicking Off the Well

Initial separation from adjacent wells. When a series of wells are
drilled from a single surface location (e.g., multiwell platform), the
first requirement is that wellpaths do not interfere with each other. It
may not seem possible, but a drill bit can cut through an adjacent cas-
ing string fairly easily. Magnetic interference high up will restrict your
use of survey tools until some separation is obtained, and in this case
a gyro surveying tool may be needed until magnetic interference no
longer occurs.
If the kickoff point is planned somewhat deeper, wells with close,
adjacent wells may be “nudged” in an appropriate direction after spud-
ding below the conductor. This gives some initial separation. The
nudge can be achieved by jetting, or with a motor or a whipstock.
Conductors can also be driven with a directional drive shoe. If it
works then the well will start off aligned away from the adjacent wells.
It is also possible that while driving, the conductor turns, and once this
starts it is impossible to stop. In the worst case, the conductor may be
unusable due to the high dogleg required to miss the nearest well.
Kickoff and build. Once the planned kickoff point is reached, the
well has to be drilled to build angle towards a particular azimuth. If the
well is a simple J profile then the kickoff will end when the well is gen-
erally pointing towards the target at an appropriate inclination.
Rotary tangent drilling assemblies often have a slight tendency to
turn to the right ( /4˚ to /2˚ /100 ft). This can be compensated for by fin-
1
1
ishing your build section slightly to the left of the line and pointing
towards the left-hand edge of the target. Increasing the rotary speed gen-
erally decreases this tendency and in some cases can actually reverse it.
Further, with a tangent BHA, using high weights to maximize ROP
may give a slight build tendency, as does drilling into formations with

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