BAKER HUGHES - Drilling Fluids Reference Manual

HORIZONTAL AND EXTENDED REACH DRILLING
The small departure and limited depth required for short-radius wells makes them suitable in
formations topped with problem-causing lithology or reservoirs.
For example, in a thin lime bed topped with 1500 feet of heaving shale, a long-radius well would
develop most, if not all, inclination in the trouble zone, while a short-radius well develops little or
no angle in the shale. Thus, in a short-radius well, a troublesome zone can be cased off before
critical hole drilling begins (see Figure 11-3).
Ultra-Short Radius Technique
The newest method of horizontal drilling is the ultra-short radius technique. This method uses highpressure
fluid to jet a semi-horizontal borehole, the radius of which turns in a matter of inches
rather than feet.
The ultra-short radius technique uses specialized equipment and requires some wellbore
enlargement in the vicinity of the lateral target. Hole sizes ranging from 2 in. to 6 in. are a function
of formation and the jetting head used, while lateral departure is limited to several hundred feet.
In limited terms, the ultra-short radius technique may be defined as a system having virtually no
build section, with a lateral placed by means other than rotary bit drilling.
Even though a hole could be jetted into hard rock, this system is clearly more suitable for soft,
easy-to-penetrate formations, such as oil or tar sands. Ultra-short methods may also be feasible for
solution mining and shallow ground water clean-up projects as well. As with any soft or
unconsolidated formation, hole stability and integrity are primary concerns (see Figure 11-4).
Figure 11 - 4
Schematic of Ultra-Short Radius
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006. 11-6