Page 140 - Practical Well Planning and Drilling Manual

Section 1 revised 11/00/bc 1/17/01 2:56 PM Page 116

[ ] Well Design
1.5.4

built in the tangent section, the left-right tolerance that is at a maxi-
mum when aligned with the target center is also increased.
One other thing to remember when planning to finish the build a
degree or two low is that building to the line (or above it) and later
having to drop angle will compromise ROP with the low weights
required for pendulum assemblies. If, however, building is needed, a
short build assembly needs weight to work so ROP will not be com-
promised. It is better to be too low than too high.
If corrections are required while drilling, they should be made
sooner rather than later. Corrections deeper down take longer and are
harder to control.
If possible, avoid having to drop angle lower down in the hole. If
circumstances dictate this, then try to avoid dropping to less than 10˚
from vertical. It will become increasingly hard to drop more angle the
closer to vertical you get.

1.5.4. Horizontal Well Design Considerations

There is a naming convention for the build rate of a horizontal
well. Long radius is less than 8°/100 ft build rate, medium radius is
between 8° and 20° and short radius is over 20° build rate. Long and
medium rate builds use conventional deviation equipment.
The build rate to horizontal you choose is very important. In gen-
eral the longer the horizontal section you want to drill, the lower the
build rate (longer the build radius).
The majority of horizontal wells, probably as many as 95%, are
drilled using medium radius builds.

Take the following into consideration when planning the wellpath:

1. If possible, select the surface location for the simplest wellpath to
the horizontal section. If you can build in the same plane as the
alignment of the horizontal section, this is preferable to designing
combined turns and builds to the horizontal. Hole drags and well-
bore instability will be less. However, with fixed surface locations
(i.e., platform) this may not be possible.
2. Avoid drilling updip horizontally if possible; drilling updip at

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