Nitrogen Talk15 May 2021 17:43
Nitrogen is found in some natural gas deposits, usually at marginal edges of petroleum pools, generated from source rock, somewhat temperature dependent. Nitrogen in these pools often less than 10%. These gas deposits can also have some acid gases like CO2 (carbon dioxide) and HS (hydrogen sulfide) that have to be dealt with, as well as hydrocarbons including methane.
The nitrogen is not a problem. The atmosphere is 78% nitrogen and 21% oxygen and traces of other gases of which argon at 0.9% is the largest component. Carbon dioxide (the big problem in terms of climate) is 0.4% and there are trace amounts of helium, neon, and methane (also a global warming problem). Important greenhouse gasses are CO2, methane, and N2O - some others.
Nitrogen dioxide is a by production of combustion and is a pollutant. (think acid rain and respiratory irritant).
N2O is nitrous oxide or dinitrogen oxide or laughing gas is in the atmosphere at about 300 parts per billion. It is the third most important greenhouse gas. There are natural sources mostly from nitrogen cycle of bacteria and fungi in soils and the ocean. There are also human sources from produced N2O that have led to 20% increase in N2O levels since 1750.
The nitrogen in the Holbrook basin is found 2 specific layers of a 28 layer stratigraphic sedimentary system that does have hydrocarbons. (mainly in the Cocino sandstone but also in Fort Apache limestone). It is probably from source rock. There is 4-10% helium and there are up to 4% CO2 and up to 2.5% methane in their well samples. There are good salt seals. Helium was produced from these layers for more than 15 years (in the past, mainly from one small area called the pinto dome) and production is being restarted by Desert Mountain Helium - higher helium price is making production there more economic
There is also nitrogen than can be "exhaled" from volcanoes in absence of sedimentary organic sources. This type of nitrogen could migrate with helium in a system totally independent of hydrocarbons. Maybe that is what is happening at Rukwa with the gas mixture trapped in conventional traps and hopefully sealed. No gas had been tested from a well (maybe soon!). The gas tested from the seeps is mainly nitrogen and helium. There are traces of other gasses.
I might also add it that not only is the geology very different in Tanzania than in Holbrook basin in Arizona - the magnitude of potential helium gas in place is many times higher. However the helium has been proven in Holbrook basin. Proving recoverable commercial reservoirs of Helium in this unique geology in Tanzania is what the excitement is all about. Helium totally independent of any hydrocarbon system migrating from the crust of the earth and being trapped and sealed in conventional reservoirs. With the nitrogen straight from volcanic exhalations? Just getting samples from wells will be amazing and very interesting to the geology scientists at oxford, I am