The effect of meteoric water on the very fine crystalline dolomite reservoir in the shallow burial zone: A case study of the Ma55 submember of Majiagou Formation in Ordos Basin

The meteoric water has obviously changed the physical properties of dolostone reservoirs in vertical vadose zone and horizontal phreatic zone, but its influence on shallow burial beneath surface is still unclear. This study aims to reveal effect through X-ray diffraction, cathodoluminescence, C, O, Sr isotope using sample from Majiagou Formation Daniudi gas field, Ordos Basin. diagenesis paragenesis Ma 55 submember were identified interpreted petrological study, combined with data electron probe, diffraction analysis, geochemical parameters diagenetic minerals. color very fine crystalline dolomite under cathodeluminescence dark red red. order degree ranges 0.54 0.91, showing origin early seepage-reflux dolomitization. There are a large number different calcite cements as fills within pores fractures. cement cathodoluminescence orange-yellow, zonal structure. Hydrothermal fluid during late could be by authigenic fluorite filling According assembly minerals, dolostones have experienced dolomitization, dissolution, cementation cementation. void spaces intercrystalline microfractures. Although dissolved caves developed period these been mostly filled multi-stages Therefore, not obvious. main controlling factor for quality reservoir was provides new understanding paleokarst period.