Page 131 - Practical Well Planning and Drilling Manual

Section 1 revised 11/00/bc 1/17/01 2:56 PM Page 107

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1.5

Directional Design

Drilling a well directionally is more expensive than drilling to the
same reservoir depth vertically. The smaller the target(s) and the more
complex the resulting wellpath, the more it will cost. Discuss the tar-
gets with the reservoir engineers and establish the largest possible tar-
get—even on a vertical well.
It may be that your target is significantly smaller than that what
would be acceptable. Exploration departments sometimes ask for a tar-
get of, say, 100 m radius simply because of “tradition.” However, it is
possible that there is room to err in a particular direction or that the
acceptable size is larger than given. Reservoir parameters rarely give
simple circles or rectangles, therefore, always ask what conditions
define the target boundary. You want to know the “hard” target, outside
of which is unacceptable and would if necessary call for redrilling part
of the well to achieve. Mark on the deviation plan all the boundary con-
ditions that constrain or affect the well, such as other wells, faults, etc.
Many people assume modern surveying tools and calculation
methods are very accurate. While this is generally true, there are limits
on performance that may come about for various reasons such as mag-

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