Page 639 - Air and Gas Drilling Manual

Chapter 12: Directional Drilling Operations 12-3
(usually horizontal) section of openhole. Early field test demonstrated that these
new modernized articulated drill string could drill horizontals out to 500 ft. These
were some of the earliest horizontal wells ever drilled. These early field tests and
operations were drilled using both drilling mud and air and gas drilling fluid
technologies. In the late 1980’s downhole positive displacement motors (PDMs)
were used to extend the capability of the ultra short-radius technology to horizontals
out to 1,000 ft. The intermediate short-radius drilling tools with PDMs are capable
of horizontals out to 3,000 ft. Short-radius technology is used exclusively for land
drilling operations. Short-radius drilling was used extensively in the 1980’s, but
have generally been replaced by the more flexible medium-radius directional drilling
technology. Short-radius directional drilling technology does not have the target
accuracy that long-radius and medium-radius drilling technologies have. This comes
from the fact that MWD technology is not very compatible with the short-radius
technology. A rough estimate is that typical short-radius tools can place the drill bit
in a 10 ft diameter target sphere located at a depth of 5,000 ft and 1,000 ft of
horizontal displacement from the vertical.
Table 12-1 gives the basic specifications of the various long-radius, medium-
radius, and short-radius drilling tools and auxiliary equipment in commercial use.
Table 12-1: Directional drilling technology specification (Baker Tool Company)
Tool Sizes (in) Bit Sizes (in) Radius (ft)
Long-radius 4 3/4 6 to 8 1/2 1000 to 1900
6 3/4 8 1/2 to 9 7/8 1000 to 1900
Medium-radius 3 3/4 4 1/2 to 4 3/4 286
4 3/4 6 to 8 1/2 286 to 300
6 3/4 8 1/2 to 9 7/8 400 to 716
8 12 1/4 400 to 716
Short-radius 3 3/4 4 1/2 to 4 3/4 19 to 25
4 3/4 5 7/8 to 6 32 to 38
4 3/4 6 1/4 to 6 1/2 38 to 42
12.2 Directional Control
Many technologies have been developed through the past seven decades directed
at improving commercial directional drilling using conventional incompressible
drilling fluids (e.g., water-based drilling muds and oil -based drilling muds). Air
and gas drilling technology has been a small niche area of the drilling industry.
Therefore, up until the late 1980’s little attention was given to the development of
directional drilling technologies for air and gas drilling operations. Although there
has been some recent development activities to develop air and gas directional
drilling technologies, these have not been entirely successful or accepted
commercially.