Frictional Drag Force
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UPPER MIDDLE |
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Fig. 4.2 : Possible directions of the normal forces in a buildup section. (After Maidla, 1987.) |
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Drag-associated tensional load can best be determined by calculating drag force on unit sections and summing them up over the entire length of the casing. Inasmuch as the maximal load is experienced while pulling out of the hole, the
calculation should proceed from the bottom of the casing in a series of steps. Each step represents the borehole sections of two consecutive stations of the directional survey.
The well profile of a typical deviated hole can be divided into three major sections (Fig. 4.1), namely :
1. Buildup. Inclination increases with increasing depth.
2. Drop-off. Inclination decreases with increasing depth.
3. Slant hole. Inclination remains constant with increasing depth.