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Casing pressure is a term used to describe the buildup in gas pressure between the casing, or outer walls, and tubing of a well. Usually, these wells are those found in the oil and gas industry. There are a number of reasons why casing pressure is important to measure and be aware of. One key reason is that excess casing pressures can cause a blowout or explosion similar to that which caused the Deepwater Horizon explosion and subsequent man-made disaster in the Gulf of Mexico in 2010.
Measuring casing pressure and making sure it does not exceed acceptable maximums is part of the job of any individual working on an oil or gas well. Casing pressure is generally measured in pounds per square inch, or PSI, because most of the tubing and casing involved in well drilling has a certain maximum PSI load that it can support before cracking, blowing out, or otherwise failing. A blowout occurs when the maximum PSI is breached and the pressure inside the well escapes from the point of least resistance. This point may be a portion of the well casing that is weaker than the rest of the casing or perhaps a joint or other natural pressure relief point.
In most cases, wells are built with blowout preventers that will relieve pressure safely when it reaches a certain point. It is still important, however, to maintain these devices and make sure they are properly functioning. A faulty blowout preventer is blamed for the Deepwater Horizon disaster, because pressure in the well head could not be relieved and was left to rise to unacceptable and unsafe levels.
Since oil and gas are under pressure naturally due to their positioning within the earth, and also because pumping equipment raises the pressure to help the liquid and gases flow through the pumping equipment to be captured, the idea that casing pressure exists is not a new one. Both the natural pressure of the materials being pumped and the artificial pressure created by the pumping equipment can combine to create unsafe or unstable casing pressures. While the tubing and casings used in oil and natural gas drilling are very strong and made of special alloys selected for hardness and strength under pressure, every metal and every substance has a breaking point past which it can no longer sustain any further load.