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A turbine is like a series of fan blades stacked on top of each other on a shaft.
Another type has a spiral-shaped steel shaft inside an elliptical opening. The bend in
the sub is from 1 to 3 degrees. This small degree of bend allows the crew to run the
tool into the hole without the tool's hanging up on the side of the hole. Although the
bend is small, it starts the hole at an angle that the crew can increase as drilling
progresses. With either tool, the crew makes up a bit on the bottom of the tool. Then
it runs the bit and the tool to bottom, as usual.
When the tool reaches bottom, the crew turns the string to get the tool to face in
the desired direction. In other words, crew members point the bend of the tool in the
direction necessary to make the hole go where they want it to. They usually do so by
using measurement while drilling (MWD) tools and techniques. MWD is similar to
LWD. To use MWD, crew members place an MWD tool in the drill string as close to the
bit as possible. As mud circulates through the string and past the MWD tool, the tool
generates pulses in the mud. These pulses move up the drill string against the down
flowing mud. Similar to the way in which radio waves carry music, voice, and other
information, the pulses transmit directional and other data to the surface. Computers at the
surface interpret the data and read it out to the directional operator.
To drill, the crew does not rotate the drill string. Instead, drilling mud flowing
through the directional motor causes the turbine blades to turn, or the spiral shaft to
turn, which rotates the bit. Once drilling gets under way, the MWD tool constantly sends
the direction the hole is heading to the surface. It also transmits the angle of the hole.

Fishing

А fish is a piece of equipment, a tool, or a part of the drill string that the crew loses in
the hole. Drilling personnel call small pieces, such as a bit cone or a wrench, "junk."
Whenever junk or a fish exists in a hole, the crew has to remove it, or fish it out. Otherwise, it
cannot continue to drill. Over the years, fishing crews have developed many ingenious
tools and techniques to retrieve fish. For example, the crew can run an overshot into the
hole to the fish. Crew members make up the overshot on drill pipe and lower the overshot
over the fish. Grapples in the overshot latch onto the fish firmly. Then the crew pulls the

overshot and attached fish out of the hole (fig. 186).
Another fishing tool is a spear (fig. 187). Unlike an overshot, which the crew
places over the fish, a spear grips inside the fish and allows the crew to retrieve it.
Other fishing tools include powerful magnets and baskets. The crew uses them to fish
for junk. Since no two fishing jobs are alike, manufacturers and fishing experts have
developed many other fishing tools to meet the unique needs of fishing crews.

Well Control

As mentioned earlier, one vital job drilling fluid should do is keep formation
fluids from entering the wellbore. If enough formation fluids enter the wellbore,
drilling personnel say that the well "kicks." A kick, if not recognized and properly
handled, can lead to a blowout. A blowout can be a catastrophic event (fig. 188). In

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