Composition Characteristics and Geological Significance of Altered Chlorite in Basalt of Emeishan,Southwestern Sichuan
Previous research has shown that a large number of chlorites are commonly developed in volcanic and clastic rock reservoirs,which affects the physical properties of these reservoirs.In order to study the influence of the genetic mechanism of chlorite alteration in volcanic rocks on reservoir physical properties,a series of basalt samples from the typical section of Mount Emei,wells ZG1,ZG2 and YT1 were selected for petrographic research and micro-area composition analysis.The results show that chlorite in basalt can be roughly divided into three crystal types:Crystalline,cryptocrystalline and microcrystalline,and generally belonging to ferroan clinochlore(diabantite)and brunsvigite,formed in an iron-rich reducing environment.The rare earth element characteristics show that the three chlorite types result from the multi-stage superposition and transformation of hydrothermal fluids and tectonic hydrothermal fluids after the magmatic stage.During their formation process,it is mainly represented by the replacement of Fe2+with Mg2+,reflecting a transition in fluid from alkaline to weakly acidic,following an intermediate acid acid variation law.The formation process of chlorites has a dual effect on the storage space of volcanic rocks:The filling and crystallization of hydrothermal fluid after the magmatic stage reduce the primary pores of volcanic rocks,thereby diminishing reservoir physical properties.Whereas the dissolution-migration of tectonic hydrothermal fluids generates new micropores,enhancing reservoir physical properties.
chloriteelectron probe analysisEmeishan basaltvolcanic rock reservoirsouthwest Sichuan
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