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STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

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Drilling Bits and Downhole Tools 823<br />

Table 4-105<br />

Rock-type Underreamers (Servco) [58]<br />

Through<br />

Casing.<br />

Inches<br />

Underreamer<br />

Eody Dia,<br />

Inches<br />

TOP.<br />

Conrmtlons,<br />

API Reg. Pin<br />

4112<br />

5112<br />

7<br />

7-518<br />

8-518<br />

9518<br />

l(1314<br />

133/8<br />

18-518<br />

3518<br />

4112<br />

5w4<br />

6<br />

7-114<br />

8-114<br />

9-112<br />

1 1-314<br />

14-314<br />

2-3/8<br />

2-718<br />

3112<br />

3112<br />

4112<br />

4112<br />

6518<br />

8518<br />

8518<br />

4314 through 6112<br />

6 through 9<br />

8 through 1 1<br />

8 through 13<br />

9 through 14<br />

10 through 15<br />

13through 18<br />

15 through 22<br />

22 through 28<br />

Courtesy Smith International, Inc<br />

Table 4-106<br />

Drag-type Underreamers (Servco) [581<br />

Model Number<br />

Specifications 57DP 72 DP 95DP 110DP<br />

Body Dia. 544, 7-114. 9-112" 11"<br />

Top Conn. 3112" 4112" 6518" 6518"<br />

Reg. Pin Reg. Pin Reg. Pin Reg. Pin<br />

Length (shoulder) 66'' 71" 57' 57"<br />

Expanded Dia. 16" 22" 28' 30"<br />

(max.)<br />

Standard Orifice Flo-Tel Flo-Tel 314" 314'<br />

Courtesy Smith International, Inc.<br />

Stabilizers<br />

Drill collar stabilizers are installed within the column of drill collars. Stabilizers<br />

guide the bit straight in vertical-hole drilling or help building, dropping, or<br />

maintaining hole angle in directional drilling. The stabilizers are used to<br />

1. provide equalized loading on the bit<br />

2. prevent wobbling of the lower drill collar assembly<br />

3. minimize bit walk<br />

4. minimize bending and vibrations that cause tool joint wear<br />

5. prevent collar contact with the sidewall of the hole<br />

6. minimize keyseating and differential pressure.<br />

The condition called "wobble" exists if the bit centerline does not rotate<br />

exactly parallel to and on the hole centerline so the bit is tilted.

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