鄂尔多斯盆地深部富铀烃源岩提供铀源可能性的实验研究

鄂尔多斯盆地上三叠统延长组长7段石油优质烃源岩以富铀为特色,而盆地侏罗?白垩纪地层以赋存大量砂岩型铀矿而著称.为探索深部长7富铀烃源岩为浅部砂岩型铀矿形成提供铀源的可能性,选择盆地南部的富铀烃源岩、油样以及具有代表性的碳酸铀酰作为反应物,在中?高温高压还原条件下分别进行烃源岩生排烃?排铀模拟实验和油?铀关系模拟实验.结...

Experimental Study on Possibility of Deep Uranium-Rich Source Rocks Providing Uranium Source in Ordos Basin

The high quality source rocks of the Chang 7 Member in Yanchang Formation of the Upper Triassic in the Ordos Basin are characterized by uranium enrichment,while the Jurassic-Cretaceous strata of the basin are famous for hosting a large number of sandstone-type uranium deposits.To analyze the possibility of source rocks providing uranium source for shallow sandstone type uranium deposits,the uranium-rich source rocks,oil samples from the Chang 7 Member and representative uranyl carbonate were selected as reactants,and simulation experiments of hydrocarbon generation and expulsion of uranium from source rocks and oil-uranium relationship were carried out respectively under the reduction conditions of medium-high temperature and high pressure.The results show that uranium can be discharged along with the process of hydrocarbon expulsion from source rock,and the increase of temperature and pressure at 30-200℃and 2-5 MPa is conductive to the increase of hydrocarbon generation and uranium discharge.The discharged rate of uranium increases with the increase of hydrocarbon generation and is generally 55%-75%.Among them,the proportion of soluble uranium from itself is about 12%,and the discharged rate of uranium caused by the superposition of hydrocarbon generation is 43%-48%.The uranium migration forms found in this experiment are special,such as tetravalent(UO₂),hexavalent(UO₃),mixed valence(U₃O₈)and hydrate colloid form(UO₃·H₂O,U₆O₇(OH)₂O),which are mainly adsorbed by low-temperature oil-gas fluid,and the uranium adsorption capacity shows an increasing trend with the increase of temperature and the decrease of pressure.Thus,it is beneficial for uranium ore formation when low temperature uranium-bearing oil-hydrothermal fluids migrate to shallow strata.Based on the above analyses,it is considered that the source rocks of Chang 7 Member in the southern Ordos Basin can release or discharge a large amount of uranium,which can be adsorbed by low-temperature oil-gas in the form of tetravalent,hexavalent and mixed valence.Subsequently,the adsorbed uranium moves upwards along with the oil-water fluid through the fracture,providing partial material source for the formation of shallow sandstone-type uranium deposits of the basin.