BAKER HUGHES - Drilling Fluids Reference Manual

HORIZONTAL AND EXTENDED REACH DRILLING
indicators, pump pressure/volume capacity, and top drive torque output. Hole issues include hole
cleaning, borehole stability, hydraulics, casing wear, and directional objectives.
Extended reach drilling from land locations has been used instead of offshore locations in several
locations including the BP development at Wytch Farm, England, and the TOTAL project in Tierra
Del Fuego.
HORIZONTAL TECHNIQUES
The industry has categorized three directional techniques as they relate to the radius formed by the
curve of the well. These are long-radius, medium-radius, and short-radius. A fourth technique,
ultra-short radius, is used much less frequently. A discussion of all of these techniques follows.
Long-Radius Technique
A long-radius well can be defined as a borehole with at least one hole section in which well
inclination is increased at 1° to 10°/100 ft. Most of these wells are drilled with conventional
downhole hardware. The kick-off point may be near the surface to allow the target to be reached at
the correct depth. Due to the length of the build section, several hole sizes and casing strings may
be necessary before the long-radius well reaches its objective. Long-radius wells are not normally
taken to the horizontal due to excessive drag and torque.
For example, a build rate of 4°/100 ft results in a radius departure of 1432 feet before the well
reaches horizontal.
The length of the radius equates to the measured depth that must be drilled to reach a given
inclination. With a 4°/100 ft build rate noted above, controlled drilling of more than 2250 feet is
required.
An explanation of these calculations follows: The drilling of 2250 feet to achieve a deviation of
90 0 which puts the drilling on a horizontal plane represents drilling ¼ of a complete circle. The
circumference of a circle is defined by 2πr. Four (4) x 2250 = 9000. Dividing 9000 by 2π gives
1432.
Medium-Radius Technique
A medium-radius lateral can be defined as a borehole with at least one hole section in which a well
inclination is increased at 10° to 20°/100 ft. A majority of the horizontal wells use this technique.
Medium-radius wells suit a wide variety of applications (see Figure 11-2), and have been
successfully drilled off-shore in the North Sea, across the Gulf Coast, in the Rockies, and on the
north slope of Alaska.
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006. 11-3