Directional drilling techniques have been used for many years to reach subsurface objectives that have had inaccessible surface locations. Economic considerations and increased environmental concerns have increased the number of directional wells drilled in recent years. Directional drilling techniques have also been applied to horizontal drilling with interest in this area increasing greatly over the last several years.

In the past, there have been two major methods utilized in planning the directional well. These methods are the use of buildup or composite buildup charts and the use of several directional well planning equations, each method depending on the particular wellbore geometry desired. The use of buildup charts is a tedious process that often yields inaccurate results since it requires using preplotted graphs that require interpretation and interpolation. The equation approach is often confusing to use due to the similarity of the various equations with the selection of the proper equation dependent on the desired wellbore geometry.

This paper presents the derivation of a single equation for planning the trajectory of any directional well and a similar equation for any horizontal well. Several examples are used to demonstrate the application of the equations to various wellbore geometries.

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