Genesis Of The Non-hydrocarbon Gas Reservoirs In Jiyang Sag

Jiyang Sag is an intercontinental extensional basin formed on the basis of a Proterozoic craton with Paleozoic cover rocks as the result of interaction between the Eurasian, Kula-Pacific and Indian plates since the Triassic Period. Jiyang Sag located east to the noted Tancheng-Lujiang rift zone. There are many CO₂ gas pools along the Gaoqing-Pingnan fault and in the Huimin Depression, attract many geoscientists' notice. Based on the previous research work, I analysis the geochemical characters of CO₂ gas pools in the Jiyang Sag and the C, O isotope of calcite veins of magmatic rocks in the Huimin Depression detailed, provide a theory foundation for the source of all the CO₂ gas pools. I obtained some conclusions by my systematic work:All CO₂ gas pools in Jiyang Sag, δ¹³C_CO2 is -5.67-3.35‰, focused in -4.76— -4.32‰, show the abiogenesis of the CO₂; the δ¹³C of CH₄ is -54.39-35.00‰, focused in -54.39-51.55‰, show the biogenesis of CH₄.All CO₂ gas pools in Jiyang Sag, the ³He/⁴He is 2.80—4.49×10^-6, focused in 3.55—4.49×10^-6; the ⁴⁰Ar/³⁶Ar is 317—1791, vary marked, focused in 770—1791; the δ¹³C_CO2 direct ratio to the ³He/⁴He; the CO₂/³He_m between 0.769—10.2×l0⁹, focused in 1.86—3.51×10⁹, and the CO₂/³He_m direct ratio to the content of CO₂ partial; the CH₄/³He between 1.01— 5.65×10⁸, closed to the mantle value, and quite lower than the crust value, and the CH₄/³He inverse ratio to the ³He/⁴He. All results above account for that CO₂ gas in Jiyang Sag have multi origin and mainly abiogenetic, and mantle is the dominating source, a few may come from biogenesis; and in the process of gas pools forming, some mantle CO₂ lost by converted to CH4 or carbonate, some crust CO₂ added into the gas pools; CO₂ gas pools in Huagou district have particular geochemical character, maybe there were some decarbonated CO₂ added into the gas pools, need further research work.δ¹³C of calcite veins of magmatic rocks in Huimin depression is -3.30—3.14‰,δ¹³O is 12.64— 16.97‰, there have direct proportion, and on the line of sedimentary contamination, show typical character of mixing between mantle and crust. The δ¹³C...