A colorless, odorless gas, Nitrogen is a non-hydrocarbon inert gas used for a variety of functions in the drilling, workover and completion phases of oil and gas wells, as well as in pigging and purging pipelines.
Used both in onshore and offshore situations, applications for nitrogen include well stimulation, injection and pressure testing, Enhanced Oil Recovery (EOR), reservoir pressure maintenance, nitrogen floods and inert gas lift. Additionally, nitrogen can be used to help prevent flammable gases from igniting and protect tubulars from downhole corrosion.
Used to support drilling operations, nitrogen can be utilized for instrument panel inerting, as well as flare gas inerting, and pressure systems purging and testing. Also, nitrogen can be supplied for the engine starters, controls, dry bulk transfer and hoisting systems. Providing a dry air supply, nitrogen can extend the life of some systems, as well as prevent breakdowns.
In workover and completion operations, nitrogen is an optimal choice to displace well fluids in order to initiate flow and clean wells because of its low density and high pressure characteristics. The high-pressure gas is also used for production stimulation through hydraulic fracturing. Also, nitrogen is used for cementing operations and controlling cement slurry weights.
Additionally, nitrogen is used to maintain pressure in reservoirs that have either been depleted of hydrocarbons or experienced natural pressure reduction. Because nitrogen is immiscible (or does not mix) with oil and water, a nitrogen injection program or nitrogen flood can be used to move missed pockets of hydrocarbons from an injection well to a production well.
Nitrogen can also be used in pigging and purging a pipeline. For example, nitrogen can be used as the driver to push the pigs through the pipe. Nitrogen can also be used to purge the pipeline after pigging has been completed. In this case, the dry gas is run through the line without the pig to dry up any remaining water in the pipeline.
Also, nitrogen can be used in FPSOs and other situations where hydrocarbons are stored. In a process called tank blanketing, nitrogen is applied to an empty storage facility, to increase safety and provide a buffer for the entering hydrocarbons.
How Does Nitrogen Generation Work?
Developed by Dow Chemical in the 1970s, nitrogen generation through hollow fiber membrane technology has progressed over the last several decades. Now, the technology offers onsite generation through various output and capacity generators. Achieving up to 99.9% purity levels, nitrogen generation has made a myriad of applications in the oil and gas field more economical.
Nitrogen is produced through patented membrane filters. The process starts by atmospheric air being taken into a rotary screw compressor. Here the air is compressed to a designated pressure and air flow. Then, the compressed air is saturated with three to five parts per million of hydrocarbons and particulates. It is then introduced into the nitrogen generation system.
The air then enters a pre-filtration system, composed of either a demister or cyclone-type water separator to remove up to 94% of free liquids.
Next, the air travels through two coalescing filters; the first is a 1.0 micron coalescing filter. And immediately, the air travels to a 0.01 micron coalescing filter. These filters remove 99.9999% of all contaminants from the air, which is still in a vapor state and saturated with water and hydrocarbons.
Ensuring the remaining contaminants are in a vapor state, the air is then heated, raising the dew point. The air now enters an activated carbon vessel, where the hydrocarbons are absorbed.
From here, the air travels through to a 0.01 micron particulate filter, which makes the air stream a specification of eight to ten parts per billion of contaminants. This guarantees a high-quality air is being supplied to the membrane modules.
Now, the air is fed to a dehydration membrane. Here, the water is removed from the recently cleansed air, reaching dewpoints as low as negative 40 degrees Fahrenheit. The dry air is then introduced to the nitrogen membranes.
In the nitrogen membranes, the oxygen is removed from the air, resulting in nitrogen at a purity level of 90 to 99%. Because the nitrogen is supplied at a 70-degree Fahrenheit dewpoint, additional residual water vapor is then removed.
Providing vast savings in comparison, onsite nitrogen generation is preferable over bulk nitrogen shipments. Furthermore, nitrogen can be created a various specifications for an assortment of uses.