Page 10 - Drilling a Straight Hole

FACTORS AFFECTING HOLE DEVIATION

Petroleum Extension-The University of Texas at Austin
Factors Affecting

Hole Deviation

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In this chapter:
• Deviation from vertical
• Formation effects

• Variation in formation drillability
• Mechanical effects
• Bit selection

here are two factors that can cause a hole to deviate from the
Tvertical—the formation being drilled and the equipment used to
drill. Both of these conditions have specific effects on hole deviation.

The type of formation being drilled affects hole deviation. Two forma- Formation Effects
tion characteristics that affect the bit’s ability to drill a straight hole
are formation dip and variation in the drillability of formations. In most
cases, these characteristics are unknown and unwanted because they
cause the bit to deviate from vertical, or walk. However, in developed
oilfields, the walking behavior of the bit can be incorporated into the
well design and the surface location appropriately shifted so the bit
deflects and drills to the desired bottomhole location.

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