RE: Interesting2 Feb 2024 23:32
Interesting, Thank you
Primary N2βHe gas field formation in intracratonic sedimentary basins
Anran Cheng1, Barbara Sherwood Lollar2, Jon G. Gluyas ORCID:orcid.org/0000-0002-9386-72063 & Chris J. Ballentine ORCID:orcid.org/0000-0001-9382-070X1
Nature volume 615, pages94β99 (2023)Cite this article
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Geochemistry
Hydrogeology
Abstract
Helium, nitrogen and hydrogen are continually generated within the deep continental crust1,2,3,4,5,6,7,8,9. Conceptual degassing models for quiescent continental crust are dominated by an assumption that these gases are dissolved in water, and that vertical transport in shallower sedimentary systems is by diffusion within water-filled pore space (for example, refs. 7,8). Gas-phase exsolution is crucial for concentrating helium and forming a societal resource. Here we show that crustal nitrogen from the crystalline basement aloneβdegassing at a steady state in proportion to crustal helium-4 generationβcan reach sufficient concentrations at the base of some sedimentary basins to form a free gas phase. Using a gas diffusion model coupled with sedimentary basin evolution, we demonstrate, using a classic intracratonic sedimentary basin (Williston Basin, North America), that crustal nitrogen reaches saturation and forms a gas phase; in this basin, as early as about 140βmillion years ago. Helium partitions into this gas phase. This gas formation mechanism accounts for the observed primary nitrogenβhelium gas discovered in the basal sedimentary lithology of this and other basins, predicts co-occurrence of crustal gas-phase hydrogen, and reduces the flux of helium into overlying strata by about 30βper cent because of phase solubility buffering. Identification of this gas phase formation mechanism provides a quantitative insight to assess the helium and hydrogen resource potential in similar intracontinental sedimentary basins found worldwide
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