BAKER HUGHES - Drilling Fluids Reference Manual

HORIZONTAL AND EXTENDED REACH DRILLING
Horizontal Techniques Summary
The single most critical aspect of horizontal and extended-reach drilling is choosing the appropriate
build rate (radius) to facilitate entrance of the reservoir at the target point. The following tables
summarize the relative advantages and disadvantages of the three main horizontal drilling
techniques with respect to reservoir/target entrance.
Short-Radius
Target Height Build Rate KOP Above TD
5 to 20 ft 1° - 3°/ft ± 25 ft
Short-radius techniques yield high build-rate predictability and good reservoir entrance control for
very thin reservoirs. Drawbacks of the short-radius system include poor directional control
(azimuth), poor correction ability, and limited lateral extension.
Medium-Radius
Target Height Build Rate KOP Above TD
15 to 100 ft 10° - 20°/100 ft ± 250 ft
Medium-radius techniques yield fair build-rate predictability and fair reservoir entrance control for
moderately thin reservoirs. However, medium-radius drilling provides for good directional control
(azimuth), good correction ability, and good lateral extension. The technique is applicable over the
widest range of conditions.
Long-Radius
Target Height Build Rate KOP Above TD
> 100 ft 1° - 10°/100 ft 1500 - 2000 ft
Long-radius techniques offer fair build-rate predictability and poor reservoir entrance accuracy.
Advantages include good directional control (azimuth), good correction ability, and great lateral
extension. The major drawback is the increased costs associated with additional target control and
measured footage.
In summary, thin reservoirs requiring little extension should be drilled using short-radius
techniques. Conversely, thick reservoirs requiring large lateral extensions should utilize long-radius
techniques. Medium-radius drilling can be applied over a wide range of applications. For this
reason, the majority of current wells employ medium-radius build rates.
DRILLING FLUID PROPERTIES AND SELECTION
It is common knowledge among drilling engineers and drillers that borehole problems can be
considerably more severe in a directional hole than in a vertical well. The problems are magnified
as the hole angle and horizontal displacement increases. Although most of these reactions are
mechanical in nature, much can be done to alleviate them by proper selection and maintenance of
the drilling fluid. For example, if a water-base fluid is being used, lubricants can be added to lower
the coefficient of friction between the drill string and borehole or casing. Inhibiting salts can be
added to reduce the interaction of the drilling fluid with the exposed formations, thereby improving
borehole stability.
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006. 11-7