Baker Hughes INTEQ

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Figure 5-57: DTU Configuration

Figure 5-57: DTU Configuration

The double tilted universal joint housing:

  • Replaces the straight universal joint housing on a standard Navi-Drill. The universal joint is slightly longer than the straight housing and universal joint.
  • Is available in various tilt angles and identified by the tilt angle, which is the mathematical resultant angle computed from the two opposing tilt angles.
  • Produces a desired bit tilt angle while reducing actual bit offset.
  • Allows for extended rotation of the motor with a low eccentricity as compared to conventional bent sub or bent housing assemblies with comparable dogleg capability. Rotation of the drill string negates the effect of the bit tilt and the assembly theoretically drills a straight, slightly oversize, hole.
  • Is available in various diameters ranging from 4-3/4" to 11-1/4".

With the exceptions of the 8" and the 9-1/2" tools, each diameter has three standard tilt angles designed to provide approximately 2°, 3° and 4° per hundred feet theoretical dogleg rates when configured with a Mach 2 motor. TGDS is theoretically higher when using the shorter Mach 1.

As illustrated in Figure 5-58, the concept behind the double tilt is that by having the two tilts in the same plane but opposed (at 180°) to each other, the bit offset is minimized. Bit offset is the distance from the center of the bit to the axis of the motor section (extrapolated down to the bit).

Drill Bits Iadc 115 Type For Oil
Figure 5-58: DTU and Bit Offset

A stabilizer can be mounted on the upper bearing housing. This stabilizer:

  • Is used to centralize the motor and bit in the center of the hole.
  • Is usually manufactured as an integral part of the housing and is referred to as the UBHS 9-1/2" and 11-1/4". Motors are available with either integral or sleeve type stabilizer UBHS.
  • Is always undergauge.
  • Has a special design to reduce drag between the blade and the wellbore, allowing sliding when the motor is drilling in the oriented mode.

The design of the UBHS includes:

  • A double taper or watermelon-shape profile with rounded edges to reduce stabilizer hangup and drag.
  • Blade widths of 3 to 4 inches to help prevent a cutting or ploughing action by the blade when drilling in the oriented mode.
  • Blade wraps varying from straight ribbed to a maximum of 30° to reduce contact area and make the stabilizer more maneuverable.
  • Gauge lengths varying from 4 to 12 inches with recommended length being less than or equal to bit gauge length.
  • Three blades at 1/8-inch undergauge for up to 17-1/2" hole sizes, or four blades at ^-inch undergauge for larger hole sizes.

UBHS with 5 straight blades are now the preferred design.

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