An Open-Hole Completion

The main parts of a completed well are the oil or gas-bearing formation, the drilled hole, many lengths of steel pipe, cement to hold the pipe in place, and a surface well-head connection.

This well on the black-and-white diagram 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 Modern Through-Casing Completion

Take a ook at these three pictures.  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 shaped 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.

After Perforation:  Fracking or Fracing

After the well is perforated, it may produce naturally if the reservoir is excellent.  Most of the time, thought, the well must be "fracked" (or "fraced," both spellings are correct) at this point.  During the fracking process, large amounts of fluids (such as water, carbon dioxide, or diesel oil) and other materials (such as sand or man-made proppant) are forced down the hole (in a procedure known as a "Frac Job"), thru the perforations, and into the producing zone.  This combination of high pressure and material fill fractures the rock, creating spaces of artificial porosity and permeability.

Fracking has been practiced extensively for over 60 years, but the word is now showing up in news articles pretty regularly.  In virtually all cases, fracking is a safe procedure which poses no risk to the the environment, or to the water quality of drinking-water wells.

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