钱家店地区油铀成矿(藏)条件对比及综合勘探意义

Comparative study on metallogenic conditions of uranium deposits and hydrocarbon accumulation conditions of oil reservoirs in the Qianjiadian area and its significance on comprehensive exploration

油气藏与砂岩型铀矿均赋存于沉积盆地中,对二者成矿条件进行对比研究,可为沉积盆地开展综合找矿工作提供借鉴。依据钱家店凹陷多年油铀兼探勘查实践资料和成果,从源、储、汇(聚)、古气候等控矿(藏)因素入手,探讨沉积盆地油铀成矿(藏)过程的相同点和差异性。研究认为,砂岩型铀矿和油气藏成矿(藏)条件类似,都需要优质的储层、隔挡层及良好的储隔组合,但二者又在物质来源、运移方式、空间展布等方面存在较大差异。砂岩型铀矿是典型的外源型、水动力运移矿床,在干旱—湿热过渡性古气候环境中有利于成矿,在盆地浅部地层更易发育;而油气藏为典型的内源型矿藏,主要受浮力作用运移成藏,成藏期受气候因素影响较小,在盆地深部地层更易保存。铀的放射性可促进地层中有机质向烃类转化,而早期生成的油气沿断裂向上逸散,又可为上部地层砂岩型铀矿成矿作用提供还原剂和矿保剂。钱家店凹陷发现的特大砂岩型铀矿,证实了砂岩型铀矿常与油气藏同盆共生,通过对比两者各自的成矿(藏)特征,总结出新生代晚期及中生代晚期兴衰的断陷盆地是油铀同盆聚集的重要场所。

Both hydrocarbon reservoirs and sandstone-type uranium deposits occur in sedimentary basins. The comparative study on metallogenic and hydrocarbon accumulation conditions of the two can provide reference for the comprehensive exploration work in sedimentary basins. Based on the practical data and achievements through years of exploration for oil and uranium in the Qianjiadian sag, the similarities and differences in the process of hydrocarbon accumulation and uranium mineralization in sedimentary basins are discussed from the aspects of controlling factors on mineralization and accumulation, such as source, reservoir, migration(accumulation) and paleoclimate. The study shows that the metallogenic conditions of sandstone-type uranium deposits and hydrocarbon accumulation conditions of oil reservoirs are similar. Both of them need high-quality reservoirs, barrier layers and good reservoir-barrier assemblages. However, there are great differences between them in material sources, migration modes and spatial distribution. Sandstone-type uranium deposits are typical exogenous and hydrodynamic migration deposits. The favorable metallogenic condition is in the transitional paleoclimatic environment of arid to hot humid climate, and it is easier to develop in shallow strata. While oil reservoirs are typical endogenous mineral deposits, which are mainly migrated and accumulated by buoyancy, less affected by climatic factors, and easier to preserve in deep strata. The radioactivity of uranium can promote the transformation of organic matter into hydrocarbons. While the oil and gas generated in the early stage escape upward along faults, which can provide reducing agent and mine-protecting agent for the mineralization of sandstone-type uranium deposits in upper strata. The discovery of supergiant sandstone-type uranium deposits in the Qianjiadian sag confirms that sandstone-type uranium deposits often coexist with hydrocarbon reservoirs in the same basin. By comparing their respective metallogenic and accumulation characteristics, it is concluded that the fault basins developed and waning in the Late Mesozoic and Late Cenozoic are important place for coexistence of hydrocarbon and uranium accumulation in same basin.