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近年来,柴达木盆地英西地区渐新统E_3~2获得了持续的重大勘探发现。基于岩心观察、系统的微观岩石学、矿物学以及地球化学分析,系统总结了柴达木盆地英西地区渐新统咸化湖盆中盐类矿物特征、成因及成藏作用:(1)英西地区渐新统E_3~24种重要的盐类矿物包括石盐、硬石膏、钙芒硝以及天青石等,或聚集成为具有一定厚度的盐层,或以矿物颗粒形式赋存于基质碳酸盐岩中。上部的盐间油层组的盐层较厚,以石盐为主,下部的盐下油层组的盐层较薄,以石膏为主;(2)盐类矿物“低锰”的元素地球化学特征、与盐类矿物伴生的基质碳酸盐岩具有的“低温成因”的碳氧同位素地球化学特征、未见热液矿物发育的岩石学特征以及分布面积极广的平面展布特征均显示了盐类矿物为典型的咸化湖盆沉积型,而非热液卤水析出型;(3)“盐”在油气成藏过程中发挥着重要作用,包括盐类矿物对裂缝的充填和防止油气逸散的封堵作用、盐层因具有很高的毛管突破压力和塑性特征而具有良好的封盖作用、地层条件下促进白云岩次生孔隙发育的作用以及占据一定的储集空间的消极作用等。这一研究成果可为盐下湖相碳酸盐岩的油气勘探提供重要的指导作用。
In recent years, the Oligocene E_3 ~ 2 in the western and western Qaidam Basin have obtained continuous major exploration discoveries. Based on the core observation, microscopic petrology, mineralogy and geochemical analysis of the system, the characteristics, genesis and accumulation of salt minerals in the Oligocene salty lake basin in the western and western parts of the Qaidam Basin are systematically summarized: (1) The E_3 ~ 24 kinds of important salt minerals in western region include Eucalyptus, anhydrite, glauberite and celestite, etc., or gathered into a salt layer with a certain thickness or in the form of mineral particles in the matrix carbonate Rock. The salt layer in the upper interbedded oil layer is thick, mainly composed of rock salt, and the salt layer in the lower sub-salt reservoir group is thin, mainly gypsum. (2) Elemental Earth with mineral salts “low manganese” Chemical characteristics, carbon-oxygen isotopic geochemical characteristics of “low temperature genesis ” of carbonate mats associated with salt minerals, no petrological characteristics of hydrothermal mineral development and extensive distribution characteristics of the surface area All show that the salt minerals are typical salinized lake sediments rather than hydrothermal brine deposits. (3) “salt ” plays an important role in the hydrocarbon accumulation process, including the effects of salt minerals on the fracture Filling and preventing the escape of oil and gas. The salt layer has a good capping effect due to the high capillary breakthrough pressure and plastic characteristics, the role of the formation of secondary pores to promote the development of dolomite and the accumulation of certain reserves The negative effects of space. The results of this study can provide important guidance for oil and gas exploration in sub-salt lake carbonate rocks.