Nobel Gas Origin And Its Oil-gas Geological Significance In The Reservoir Inclusions Of Konggu Oil Field In Huanghua Depression

Carbonate rock samples of the Ordovician are collected from the different tectonic units, i.e., the Huanghua depression, the Ordos basin and the Tarim basin. On the basis of measuring the elements, the temperature of inclusion and thermal weightlessness of the samples, the isotopic abundances and ratios of noble gases of different states were measured using vacuum stepped-heating. Integrating the tectonic backgrounds and the isotopic characteristics of noble gases in mantle-sourced rocks of the research area, the origin and source of noble gases from the Huanghau depression were analysed and the tectonic and petroleum geological significances of noble gas isotopes in carbonate inclusions were discussed. The following conclusions are reached:1. The abundance of ⁴He, ²⁰Ne,⁴⁰Ar, ⁸⁴Kr and ¹³²Xe in carbonate inclusions of different tectonic backgrounds in different heating ranges are all increased with the temperature rising. At the heating phase from 160 to 350℃ and 350 to 650℃, the abundance of noble gas isotopes of the samples is all higher than the corresponding value of the heating phase from 80 to 120℃ and 120 to 160℃. The noble gases which released at 900 to 1200℃ heating phase are from the carbonate remains and its abundance changes very large.2. Majority of ⁴He/²⁰Ne ratio of the inclusions of carbonate rock samples from different tectonic backgrounds is more than two orders of magnitude higher than air's corresponding value, therefore the helium from air may be neglected. The ³He/⁴He ratio changes from 3.083 ×10^-6 to 3.82×10^-6 in Well Konggu 7 of the Huanghua depression, which varies between crust and mantle's corresponding values, which means that the helium is from the crust and mantle. The ³He/⁴He ratios of the Ordos basin and the Tarim basin are low relatively, which mainly varies between 2×10^-8 and 10.6×10^-8, representing a typical crust origin.3. The ²⁰Ne/²²Ne ratios change from 10.46 to 11.5 in Well Konggu 7 of the Huanghua depression, which varies between air and mantle's corresponding value, similar to the corresponding values of inclusions from the mantle-derived rocks of the east part of China. This means that the neon has a mixed origin of the air, crust and mantle. The ²⁰Ne/²²Ne ratios in Well Tian2 of the Ordos basin and in Well Lunnan46of the Tarim basin are higher than air's, therefore we presumed that it may be the results of 19F(n,a)22Ne nuclear reaction which produces little 22Ne in carbonate rocks.4. The Ar/ Ar ratios of different carbonate rock samples are conform to the air's in the error range, which shows that the 38Ar and 36Ar fractionation effect is not prominent and it results in the change of 38Ar/36Ar ratio in a narrow range in different circles of the earth. The Ar/ Ar ratios in different temperature phases change from 260 to 483 in Well Konggu 7 of the Huanghua depression, which is close to or higher than air's, representing a mixed origin of air, crust and mantle. At the heating phase from 900 to 1200°C, the 40Ar/36Ar ratios are higher relatively and they change from 528.6 to 735.9, which may be a result of high K2O content of carbonate remains. The changing range of 40Ar/36Ar ratios in Well Lunnan46 of the Tarim basin and in Well Tian2 of the Ordos basin is narrow, varying between 380 and 307, which is close to the air values.5. The 82Kr/84Kr ratios of carbonate samples change from 0.124 to 0.255, the 83Kr/84Kr ratios vary from 0.146 to 0.224, the 86Kr/84Kr ratios change between 0.269 and 0.366, the 129Xe/130Xe ratios change from 5.42 to 6.86;the 13IXe/130Xe ratios vary from 4.14 to 7.20, the 132Xe/130Xe ratios change from 4.62 to 8.24, the 134Xe/130Xe ratios change from 1.62 to 3.01 and the 136Xe/130Xe ratios change from 2.06 to 2.34 in Well Konggu 7 of the Huanghua depression. All these ratios are close to those of the air, and the characteristics -of their distributions conform to the krypton and xenon isotopes which from the mantle-sourced rocks of the east of China, showing a mixed origin of air and mantle. The data of krypton and xenon isotopes in Well Tian2 of the Ordos basin and in Well Lunnan46 of the Tarim basin are fewer, which is close to the corresponding values of air in an error range.6. Comprehensively we hold that the mantle-sourced noble gases in the carbonate reservoir inclusions from Well Konggu7 of the Huanghua depression should be the mantle fluid which was formed by the mixture of a great deal of air and ocean crust matter formed by the subduction of the Mesozoic and Cenozoic Pacific plate under the Asia-Europe plate under the east of China with some upper mantle substance there and the migration along a deep fault.7. Integrating the temperature measured from inclusions with a hydrocarbon generating evolutionary history, we thought that the intrusive periods of noble gas into inclusions is the Late Triassic, the Early Jurassic to the Late Cretaceous and the Cenozoic, which is consistent with the phases of tectonic movement of the east part of China. The characteristics of noble gas isotopes of carbonate reservoir inclusions in the Huanghua depression may indicate the regional tectonic movement, the crust and mantle interaction, paleotemperature and the conditions of forming oil-gas reservoirs.