STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

Drilling Bits and Downhole Tools 819
Table 4-103
Christensen’s Mason Drilling Jar
I I I I 1
Courtesy Hughes Christensen.
I
II
I I . .O 0 I I I .....
Included in the drill string, the Hevi-Hitter jar can fire either upward or
downward. The jarring force, which can exceed 700,000 pounds on the larger
sizes, can be controlled from the surface by applying and holding right-hand
torque to increase impact, and by applying and holding left-hand torque to
decrease impact. Because the Hevi-Hitter jar recocks automatically, jarring
operations can proceed swiftly until the stuck pipe is free. Various impact forces
can be generated dependant upon weight of drill collars (or heavy weight drill
pipe) above the jars and the value of surface pull, as shown in Table 4-104 [57A].
Underreamers
The term “underreaming” has been used interchangeably with “hole opening.”
Underreaming is the process of enlarging the hole bore beginning at some point
below the surface using a tool with expanding cutters. This permits lowering
the tool through the original hole to the point where enlargement of the hole
is to begin.