Multiphase Diagenetic Processes and Their Impact on Reservoir Character of the Late Triassic (Rhaetian) Kingriali Formation, Upper Indus Basin, Pakistan

Multiple episodes of dolomitization the shallow marine carbonates Late Kingriali Formation resulted in regional scale mappable dolostone geobodies Kohat and Potwar sub-basins. With exception few unaltered patches host limestone, more than 90% studied formation are diagenetically altered by replacive dolomites with associated dolomite cementation. Petrographical geochemical data interpretation reveals that during initial stage dolomitization, precursor limestone was significantly modified fabric-retentive (RD-I) produced bulk dolostones non-planar-a to planar-s crystals. Neomorphic recrystallization (RD-II) observed as an overgrowth already formed RD-I crystals progressive dolomitization. The seawater at depths is enriched Fe-ions due its interaction Fe-rich beds within formation. actively participated ferroan (RD-III). Stable isotopic composition Echinoderm plates, calcite cement (CC-I), demonstrates signatures ?18O ?13C limit late Triassic or seawater. Depletion stable oxygen (from ?0.99‰ ?3.75‰ V-PDB) RD-II RD-III were a sequence progressively higher temperature fluids normal Precipitation cements cavity filling rhombs (DC-I) crystal (DC-II) highly depleted values (?5.44‰ ?7.45‰ illustrates cementation temperatures greater depths. (up ?9.16‰ 0.42‰ for saddle (SD-I) indicate precipitation SD-I considerable depth. Calcite calcitization early, middle, diagenetic modifications interpreted from their petrographic studies. Porosity enhancement clearly demonstrated dissolution, stylolization, fracturing, replacement Dolomite had negative impact on reservoir character occluded porosity extent.