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breaks a membrane on the bottom plug and opens a passage. Slurry then goes through
the bottom plug and continues down the last few joints of casing. It flows through an
opening in the guide shoe and up the annular space between the casing and the hole.
Pumping continues until the slurry fills the annular space.
As the last of the cement slurry enters the casing, a crew member releases a
topping from the cementing head. A top plug is like a bottom plug except that it has no
membrane or passage. The top plug separates the last of the cement to go into the casing
from displacement fluid. Displacement fluid, which is usually salt water or a specially
formulated drilling mud, moves, or displaces, the cement from the casing as the cement
pump applies pressure to move the cement and fluid down the casing.
Continued pumping moves the cement, the top plug, and the displacement fluid
down the casing. Most of the cement slurry flows out of the casing and into the
annular space. Soon, the top plug seats on, or bumps, the bottom plug in the float collar.
When it bumps, the pump operator shuts down the pumps. Cement is only in the casing
below the float collar and in the annular space. Most of the casing is full of displacement
fluid.
After the cement company pumps the cement and removes its equipment, the
operator and drilling contractor wait a specified time for the cement to harden. This
period is referred to as "waiting on cement" or simply WOC (pronounce each letter).
WOC can vary from a few hours to several, depending on the cement formulation,
well temperature, and other factors.
After the cement hardens, the operator usually runs tests to ensure that the cement
job is satisfactory. If it is, then crew members can get back to drilling. If it is not, the
cementing company uses special remedial procedures to alleviate the problem.
Remedial cementing involves determining the depth of the problem and then, by using
special equipment, placing cement at that depth to rectify it.

Tripping in

Once a good cement job is obtained, drilling can resume. The operator selects
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a bit that can go inside the surface casing. If, for example, the crew ran 3/ s-inch
(346-millimetre) casing inside a 200-millimetre hole, then they would probably
run a 311.2-millimetre bit into the casing to drill the next stage of the hole. As
before, crew members make up the new bit on the end of a drill collar and run it
into the hole on more drill collars and enough drill pipe to get the bit to bottom. This
process is known as "tripping in." To trip in, the rotary helpers stab a stand of
pipe into the suspended stand. They then spin up the joint with a spinning wrench.
With the pipe spun up, crew members use the tongs to buckup the joint to final
tightness.
Some rigs have an "Iron Roughneck™," which is a large machine that the
floorhands use to spin up and buck up drill pipe joints. And some rigs have
automatic pipe rackers, which run pipe into the hole with special gripping arms
and a built-in spinning wrench and tongs.

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