Deflection Tools
Although mud motors and rotary steerable systems are overwhelmingly the tools of choice for controlled directional drilling, there are other tools that may be of some use in certain areas. These include:
- Directional wedges
- Jet bits with oriented nozzles
Directional Wedges
Figure 1 shows a schematic of the wedge technique for deviating a wellbore.
The wedge is attached to the bottomhole assembly by means of a shear pin. The assembly is lowered to bottom and oriented in the proper direction. The driller applies weight to set the wedge and shear the pin, drills ten to fifteen feet of undergauge hole, and then trips the tools so that a full-gauge hole opener can be run. After drilling the section, a survey is made to assure proper direction, and the process is repeated until the build section of the well is completed.
The directional wedge technique is time-consuming, has limited applications, and requires a high degree of technical expertise to properly implement. For these reasons, it is seldom used.
Jet Bits with Oriented Nozzles
Jetting bits with orienting nozzles can be effective at initiating deflection in very soft formations. Figure 2 illustrates the technique.
The bit is lowered to bottom , the jet is oriented in the desired direction, and mud flow is initiated with no drill string rotation. After hydraulically gouging a small pilot hole (about 3 feet), the driller initiates conventional rotary drilling to open the section to full gauge. The process is then repeated. Hole surveys are made after drilling 10 to 15 feet of build section.
