Page 637 - Air and Gas Drilling Manual

Chapter
Twelve

Directional Drilling Operations

Planning is the most important factor in any directional or horizontal drilling
project. All directionally drilled wells have to accurately placed in a three-
dimensional target area. These directional drilling projects depend upon providing
the operation with drilling fluids that will adequately clean the borehole of drill bit
generated rock cuttings. This is especially the case when drilling a horizontal
section in a directional well. Directional wells have been drilled using compressed
air and natural gas, aerated (or gasified) incompressible drilling fluids, and stable
foam drilling fluids.
12.1 Introduction
Directional drilling is generally categorized by the build angle rate of the
directional portion of the borehole. These categories are stated in borehole angle
build rate from the vertical per 100 ft (or per ft). Figure 12-1 shows a schematic of
the three generally accepted categories of directional drilling. The figure shows three
boreholes drilled to the ultimate high angle of approximately 90˚ from the vertical.
These three categories are long-radius boreholes, medium-radius boreholes, and
short-radius boreholes. All three of these directional drilling build rate categories
have unique downhole and surface equipment.

12.1.1 Long-Radius Drilling
In the early years of rotary drilling (i.e., the late 1920’s), long-radius directional
operations was the only directional method available for drilling controlled deviated

12-1
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