Nitrogen Gas Reservoirs

[mona_2010]

Hi Everyone, I have a query on nitrogen gas reservoirs.

We work with dry gas reservoirs with mostly above 97% methane content. We had been drilling in various fields for over 30 years and all the reservoir gas were found to be of the same composition.

Lately, we have come across an RDT sample from a particular well that yielded 99.78% nitrogen along with very minor amounts of C1 and carbon dioxide. Is it possible that there might be presence of the nitrogen gas reservoir/ local pool amid all the highly methane rich reservoirs discovered as on date. Literature survey shows that there are such basins with almost 100% nitrogen content in Northern Germany. I do not have access to the papers that would help me dig more into the matter.

Does anyone have similar experience with nitrogen reservoirs? Is there any specific log signature for such kind of reservoirs? What I found was a coarsening upward sequence type.

Unfortunately, I do not have access to the cuttings and no coring was done in the well. The gas sample is also not presently available. Under such circumstances, how do I confirm whether or not it is a nitrogen gas reservoir.

Kindly help.

[vinomarky]

I think you'll find the presence of nitrogen has less to do with the reservoir geology, and more to do with the age and proximity to deep mantle and/or igneous bodies.

There's an interesting article titled "UNDERSTANDING SOURCE, DISTRIBUTION AND PRESERVATION OF AUSTRALIAN NATURAL GAS: A GEOCHEMICAL PERSPECTIVE" in the 2001 APPEA Journal that you may want to see if you could get a hold of.

The German situation, from what I've read, is related to inorganic cation exchange reactions between potassium and ammonium. The substitution of ammonium for potassium in clay minerals during diagenesis, the release, migration and oxidation of which gives rise to N2 - Again though, it is not so much related to the reservoir in which you find the accumulations, rather the kitchen,

[kochichiro]

Well maybe I am a little off topic, but is there any way to commercial application of such kind of reservoirs (of course if it would exists). I just curious….

[vinomarky]

I'd say it would be unlikely. The atmosphere is 78% N2 anyway, so unless you had freakishly high N2 levels AND very close proximity to an industrial gas company I'd say the economics just would not stack up. Generally, high levels of N2 normally mean you have to factor in a $250mm+ nitrogen rejection unit (essentially a cryogenic facility) into your FDP. Now Helium.... that's a different story, you can make some good money there given right conditions :-)

[darcyoil]

Vinomarky is absolutely right. We have the same disturbing problem in the Jaisalmer basin. Lovely anticlines. Great reservoir properties. All N2.