Nitrogen is an odorless, colorless, nontoxic gas, which makes up approximately 78 percent of the earth's atmosphere. Gaseous nitrogen is taken from the atmosphere and processed into a liquid. To convert liquid nitrogen into a usable gas to be used for downhole or surface applications, the liquid must be pumped through a heat exchanger (nitrogen unit) at a controlled rate enabling it to be used for a wide variety of applications. Being completely inert in its gaseous form, nitrogen does not react adversely with any treating or formation fluids and is only slightly soluble in oil, and other liquids. Nitrogen's desirable physical characteristics allow application in many well services during drilling, completion, and workover operations. Nitrogen's liquid boiling point is -320 deg F, therefore must be contained in large thermos like bottles/tanks. The inner tank is made of stainless steel, which has little or no expansion properties. The outer shell generally is carbon steel and is separated from the inner shell with webbing. Insulation such as perlite is blown in between the two tanks. The tanks are then sealed and a vacuum imposed between the two. Since one gallon (approximately 0.14 cubic feet) of liquid nitrogen makes 93.11 standard cubic foot (SCF) of gaseous nitrogen, it is easy to see that nitrogen is a highly expanding gas. As it changes back to a gas state, all vessels holding liquid nitrogen are either vented continuously or are shut in with pop off type safety valves protecting the vessels against rupture.
Nitrogen can be used for the following applications; some through coiled tubing and others on a standalone basis: pipeline commissioning, production tubing displacements, drill stem testing, jetting through gas lift valves, atomizing acid, nitrified acid, foamed acid stimulation hydraulic fracturing, stable foam fracturing, pressure testing, surface testing, pressure maintenance, nitrogen assist drilling, foam drilling, foam – cementing, atomized inhibitors, hydrostatically differential stuck pipe, injection wells-backflow for cleanup, scale removal with foamed acid, setting hydraulic packers, annular insulation, hydraulic perforating, and perforating under nitrogen pressure.
PES nitrogen units are manufactured by Hydra-Rig and are rated for 15,000 psi with pumping capacity of 3000 standard cubic foot per minute.