Research Progress on Dynamic Transport and Accumulation Coupling Mechanism of Crust-sourced Helium Gas Across Rock Strata

Abstract

As an important scarce strategic material, helium is an associated resource in natural gas, but its enrichment mechanism is not well studied. Based on the analysis of helium enrichment in major helium-rich gas reservoirs at home and abroad, aiming at the difficult problem of how to enrich helium in the helium-rich gas reservoirs that have attracted much attention, helium in natural gas is mainly caused by shell source radioactivity, the distribution of helium-rich gas is closely related to ancient granite or ancient basement, and the occurrence modes of helium are mainly water-soluble and free-form. A large amount of ancient formation water is one of the main controlling factors of helium enrichment in natural gas. The basement granite of the basin can be used as the effective helium source rock of the helium-rich natural gas reservoir, and the organic-rich shale can also be used as the helium source rock. The main reservoir-forming models of shell source helium are helium-magma-rich gas reservoirs. Helium-groundwater - helium-rich gas reservoir formation model; Helium gas accumulation model in geothermal field. The important mechanism of helium enrichment is that the ancient formation water dehelium enrichment, helium dissolved and preserved in water, accompanied by late tectonic movement, resulting in fracture, stratum rise, and stratum movement above water. Under the action of Henry's law, the dissolved helium in water decreases with temperature and pressure and is released into the gas reservoir, forming helium-rich natural gas reservoir. By studying Henry's law, the proportion of water soluble and free states in helium migration is analyzed. It is concluded that helium dissolved in the pore water of surrounding rock diffuses to the migration gas, and most of the helium and nitrogen in the pore water are decomposed into the migration gas, and even the gas dissolved in the shale pore water near the gas reservoir. This process concentrates the helium in the gas, and highly enriched helium is more likely to form in shallow layers; A cooler temperature gradient is more conducive to helium enrichment in the gas.