Exercise Deviation in Vertical Wells
Briefly describe how the pendulum assembly and packed-hole assembly work to control wellbore deviation.
Solution
pendulum assembly: employs a stabilizer to center drill collars at some point above the bit. When the stabilizer is correctly placed, the pendulum length will be substantially greater than it would be in an unstabilized BHA, thus increasing the restoring or straightening force.
packed-hole assembly: employs large-diameter drill collars and multiple stabilizers to provide added stiffness to the bottomhole assembly.
Assessment Deviation in Vertical Wells
1. Which of these formation characteristics is LEAST likely to affect hole deviation?
A .Porosity ✔
B .Dip angle
C .Anisotropy
D .Lithology
2. Which of these statements is FALSE?
A .The drill string design is a key to controlling wellbore deviation.
B .Bit/rock interactions have a negligible effect on wellbore deviation. ✔
C .The extent to which drill string buckling occurs depends both on its rigidity and length.
3. Which of these components characterizes a packed hole assembly?
A .A downhole mud motor
B .A single stabilizer placed two joints above the bit
C .Multiple stabilizers and large-diameter drill collars ✔
D .One or more reamers
4. Which of these techniques can be used to reduce drill string buckling tendencies, and thus minimize uncontrolled borehole deviation?
A .Place stabilizers at selected points in the bottomhole assembly.
B .Use large-diameter drill collars.
C .A and B. ✔
D .None of the above.
5. A pendulum assembly is used to __________.
A .Build hole angle
B .Drop hole angle ✔
C .Maintain a constant hole angle
D .Reduce drill string torque
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