An Open-Hole Completion
The main parts of a completed well are the oil or gas-bearing
formation, the drilled hole, manyl lengths of steel pipe, cement to hold the pipe in
place, and a surface well-head connection.
This well to the right is completed "open-hole", meaning there is no
casing over the oil or gas zone. This is a very primitive way to complete
a well.
A modern well is completed with steel casing set over the oil zone.
Holes are shot through it to let the oil and gas in. See the picture
immediately below.
A
Normal Through-Casing Completion
Look at the picture to the left. After
it has been decided that the well will be "completed", steel pipe is run all the way to the bottom of the hole
and cemented in place. This stops oil, gas, and salt water from coming into the
hole from formations above the pay zone. There
will already be some steel pipe in the well immediately after drilling.
"Surface Pipe" usually extends from the surface to about 1000' deep to
protect ground water. An "intermediate string" may have been run
to a depth of several thousand feet if there was a need to keep the hole from
collapsing during drilling. Often last few thousand feet of the hole is
still open, so the "production casing" will be run to cover this
interval.
Then a device called a
"perforating gun" (A) is lowered
into the hole at the depth where the oil or gas formation is found. This may be
anywhere from several hundred feet down to tens of thousands of feet.
After the gun is lined up properly, powerful explosive charges are
fired (B) from the control panel in the truck...up at ground level. These explosives
blast a hole in the steel casing and cement, up to several feet out into the
rock. Finally, the oil and gas fluids flow
into the holes and up the well to the surface (C).
This method of completion is much better than the old open-hole
method shown in the first picture. The PG is able to control exactly where the
perforations go. This helps her to limit the amount of undesirable fluids, like salt
water, entering the hole, and maximize the amount of hydrocarbons that
can be removed from the well.
If
the workers feel the well is capable of producing oil, a Beam Pumping Unit (left)
will be placed on the well.
Completed Well and Perforation diagrams, Primer of Oil and Gas Drilling
Beam Pumping Unit Diagram, Modern Petroleum
