Page 142 - Practical Well Planning and Drilling Manual

Section 1 revised 11/00/bc 1/17/01 2:56 PM Page 118

[ ] Well Design
1.5.5

7. Plan to use less build rate than is possible with the downhole equip-
ment. This gives some leeway if an increase in build rate is needed.

1.5.5. Multilateral Wellbores

At the time of this writing, the technology of drilling a number of
“daughter” wellbores from a single “mother” well is developing rapidly.
These techniques are applicable if the cost of carrying out the procedure
is less than the net present value of the extra hydrocarbon production
rate and/or enhanced recovery volume. In some cases, existing wells can
be reentered and laterals drilled out from the main bore.
Multilateral wells may be applicable for:

Exploiting stacks of layered but separated reservoir sands
Allowing more footage in the reservoir than would be the case with
a single horizontal wellbore
Using existing wells to recomplete in new zones that could not be
exploited from the existing wellbore direct
Downhole water separation and reinjection in a different lateral

If this might be applicable to your planned well, early discussions
with the reservoir engineers and directional service company should be
initiated. At present the technology is still quite young.

1.5.6. Slant Rig Drilling

One other consideration is perhaps worth mentioning here. Special
rigs can be used that allow the well to be spudded at a surface inclina-
tion up to 30˚. A good example of this was the British Gas development
of Morecambe Bay. The reservoir was shallow but required fairly high
stepouts. Drilling conventionally deviated wells would have required
two platforms, which would have made the economics marginal.
Instead a special rig package was put on the platform where the derrick
could be inclined. Three conductors were driven at an angle in each
corner of the platform through which the wells were spudded. Current
high angle and horizontal drilling technology gives us much greater
flexibility in exploiting these fields economically; however, there is still
a place in our armory for innovative solutions such as slant rigs. (There
is the story of the derrick man who got off the chopper in Morecambe

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