Page 132 - Practical Well Planning and Drilling Manual

Section 1 revised 11/00/bc 1/17/01 2:56 PM Page 108

[ ] Well Design
1.5.1

netic anomalies. Minimum curvature calculations assume a perfect arc
between survey stations, although that will rarely be the case. These
factors limit how accurately you can know the actual wellpath and
gives a “cone of uncertainty” that increases in size as it gets deeper and
within which should lie the true wellpath. This also limits how close
you can plan to go to any particular boundary condition. How quickly
this cone expands depends on your surveying instruments and, if it is
critical, should be discussed with the surveying equipment vendor.

1.5.1. Planning the Wellpath

To start planning the deviation (or asking the directional service
company to present a proposal), the following information must be
available:

Surface coordinates and the system used in defining them.
(Lat/longs on a certain projection; local grid coordinate system,
etc.)
Target TVD and the outside boundary that defines the target area
Any other limitations on the wellpath, such as adjacent wells
Proposed hole sizes and casing setting depths (vertical)
Offset information from other wells showing directional perfor-
mance of BHAs through the same formations and formation
dips/directions, if known
Geological sequence
Rig information: maximum derrick loads, mud pump details,
drillpipe, DCs and directional equipment available
Any other relevant information including your own requirements
(such as type of well profile, wellbore inclination through the
reservoir, etc.)

Keep it simple. The simplest will be the easiest and cheapest to
achieve. Further, involve the directional company from the earliest
stages of planning. Most directional companies have their own dedi-
cated engineering departments to assist in well planning. However,
beware of expensive, high-tech suggestions if you think that cheaper
techniques are viable.

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