Triplex Pump

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Frequently Asked Questions...

liquid nitrogen explosion at oil well- causes?

What are the possible causes of a truck of liquid nitrogen exploding at an oil well site? My step-son was just killed in such an incident yesterday and we can't get any details. Does anyone have any experience in this field to give an educated guess as to what might have gone wrong? We don't know if he was in the truck moving it or out of the truck doing something else. I'd appreciate any insight.
They were not putting out a fire. They were somehow cleaning the well.


Best Answer...

Answer:

My deepest sympathies for your loss. I hope I can provide a small amount of information as you requested.

Nitrogen is inert, meaning it does not react with other materials. It definitely will not burn. It can be used on an oil or gas well location for several things. Most likely, since you said cleaning, it was being used to remove debris from the well bore. This is done by pumping nitrogen down the tubing as it is lowered into the well. If the well was under pressure, there is a good chance coil tubing was being used, The nitrogen then blows debris at the end of the tubing back up the outside of the tubing and out of the well. Valves and other connections are used to control and direct this flow. This can be reversed where the nitrogen goes down the tubing-annulus (outside of the tubing) and comes out the tubing. This is also done to remove water that has accumulated in the well to help the well begin to flow oil/gas by itself. This works similar to blowing air from a nozzle. Air is not used as it can result in an explosion (21% oxygen + oil/gas + 1 small spark) and it is also corrosive to the tubing in the well.

The nitrogen is transported to the wellsite as a liquid. As noted in one of the answers above, it is kept very cold to keep it as a liquid. On location, the nitrogen is connected to a high pressure triplex pump. It is then vented through the pump to cool the hoses/piping/connections and the pump itself. The liquid nitrogen is then pumped, usually at a relatively high pressure (1000 to 10,000 psi) through a heater on the back of the nitrogen pump truck where it is converted to gaseous nitrogen. It then travels down high pressure treating iron (thick heavy pipes) to the well head or another unit at the well head which is connected to the downhole tubing.

Several things could have created the failure. First, if a valve downstream of the nitrogen pump was closed while the pump was pumping, the weakest point between the pump and the closed valve would have failed. This could have resulted in deadly flying debris, which could have hit an operator or penetrated the nitrogen tank. This does not happen often, but has happened numeorus times in the past.

The tank holding the liquid nitrogen could also have failed due to a problem with the automatic vent valve and the other pressure relief valves allowing the tank to overpressure and fail. These are designed, installed,and regularily tested to make this a remote possibility.

If the wrong type of connection was used anywhere downstream of the pump, it could have failed at a low pressure, resulting in the same problem as mentioned in the first scenerio. Many of the connections used in the oil field look similar and even fit together, but if you use a low pressure connection under high pressure it will come apart.

The iron mentioned above, which the high pressure nitrogen is pumped through can become like a giant whip if it fails. This could severly hurt someone if it hit them. It could severly damage a nitrogen tank if it hit the tank.

Although there would be no fire, if the liquid nitrogen tank suddenly failed . The liquid expanding into a gas instanteously would be similar to a bomb going off.

The two companies mentioned in the news article have safety programs, policies, and procedures that border on extreme. Both should have standard operating procedures that when followed, prevent an accident like this from occurring. I strongly suspect you will find training issues and policy violations contributed significantly to this accident. I wish you the best in uncovering the truth.