BAKER HUGHES - Drilling Fluids Reference Manual

HORIZONTAL AND EXTENDED REACH DRILLING
Figure 11 - 3
Schematics of Wellbore Radius in Unstable Formations
Other advantages include reduced torque and drag. Also, no special equipment is necessary as in
the case of the short-radius well. As a result, more equipment is available for these types of
wellbores.
An unstable or problematic formation yields the most unpredictable variation in build rate and
vertical target accuracy. This situation is one of the most influential factors in determining which
horizontal technique to use.
Many troublesome zones are normally penetrated in the vertical section of a medium-radius well,
and can be cased off before drilling the build and lateral sections. The shorter length of curved
wellbore has proven less troublesome to operators than extended-reach wells (see Figure 11-3).
Short-Radius Technique
Short-radius drilling encompasses a wider range of build rates than any of the others discussed.
Short-radius drilling is best defined by the use of flexible or articulated tooling to drill doglegs
ranging from 1° to 3°/ft.
The best use of this technique is for wells in leases of limited size. A short-radius and/or re-entry
well could be turned to lateral and completed with less displacement than a typical long-radius well
at 45°. This would make short-radius drilling quite attractive on leases less than 80 acres in size.
Problems with this technique involve small hole sizes, downhole tool problems, and being able to
hit a small target with consistency. Other difficulties involve completion techniques.
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006. 11-5