Can authigenic pore-lining chlorite restrain quartz overgrowth in clastic reservoir? a case study of sandstone reservoir in Xujiahe Formation,Sichuan Basin

The composition and content of clay minerals in 395 rock samples from sandstone reservoir in Xujiahe Formation,Sichuan Basin are examined by a combination of X-ray diffraction,thin section casting,scanning electron microscopy,energy spectrum analysis,and trace element assays.Results show that illite and chlorite are the major clay minerals in sandstone reservoir in Xujiahe Formation.Chlorite accounts for 33% of total content of clay minerals and has a positive correlation with porosity and permeability of reservoir.The authigenic chlorite is iron-magnesium transition type,which contains abundant iron and is mainly developed on grain surface of sandstone skeleton in the form of foliated and needle-shaped lining.Authigenic chlorite is formed in alkaline aqueous solution at pH7-9,whereas quartz overgrowth occurs in weak acidic aqueous solution at pH5-6.Different symbiotic relationships between authigenic chlorite and quartz are resulted from variations of aqueous medium condition.The presence of authigenic pore-lining chlorite could not restrain quartz overgrowth significantly,and authigenic chlorite preferentially grows in sandbodies with macropore spaces.