Interesting article17 Dec 2024 00:50
Although the source of radioactive helium gas is relatively single, resulting from the continuous decay of U and Th, almost all rock layers can produce helium. On the contrary, nitrogen has diverse and complex sources with different pathways and mechanisms of generation. Despite these differences, they are frequently enriched simultaneously in helium-rich gas reservoirs, a phenomenon observed consistently rather than accidentally. Many researchers have realized that helium-rich gas reservoirs contain high levels of nitrogen. The latest recent findings by Krooss et al shows that the enrichment of radioactive helium in natural gas is directly related to nitrogen.
This study shows a clear symbiotic relationship between helium and nitrogen in major helium-rich gas fields worldwide, demonstrating a positive correlation between their content with a high correlation coefficient. Based on this correlation and current research insights into the enrichment mechanism [12] and enrichment mode [13] of radioactive helium, it is proposed that helium enrichment in these reservoirs exhibit a coupling effect with nitrogen.
The coupling effect between helium and nitrogen enrichment manifests in several ways. First, the content of these gases in the reservoir is closely interconnected. Second, they share the same transport carriers, utilizing common groundwater, ultimately becoming enriched in the gas reservoir. Third, driven by tectonic uplift, groundwater migrates upward along faults to the gas reservoir, releasing helium and nitrogen gas. Alternatively, water-soluble gas reaches saturation in groundwater due to the temperature and pressure drop during upward migration, releasing free gas. Fourth, helium and nitrogen may have a common source rock, especially ancient basement rocks. Helium gas results from the decay of U and Th in the source rock, while nitrogen originates from the decomposition of nitrogen-containing compounds in the source rock.
The formation of helium rich gas reservoirs follows the process of “multiple sources supplying helium and main sources enriching helium”. While helium can originate from the radioactive decay of U and Th in source rocks and reservoirs, but the main source is dissolved helium in ancient formation water, and water-soluble helium accumulated through long-term decay of U and Th in ancient formations [12]. Simultaneously, as ancient strata generate helium gas, nitrogen-containing compounds within these strata undergo high-temperature decomposition, producing helium gas that also dissolves in the formation water. With the uplift of structures and the development of faults, the formation water containing dissolved helium and nitrogen gas moves upward, releasing helium and nitrogen gas into the gas reservoir, forming a helium-rich gas reservoir with a certain amount of nitrogen gas.
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