Petrographic Characteristics and Fluid Inclusion Study of Carbonate Cements in Permian-Triassic Rock Sequence of Southern Iran: an Implication of Rock-fluid Interactions in Carbonate Reservoir Rocks

The study of the carbonate cements in the Permian-Triassic Dalan-Kangan formations resulted in the identification of five stages of calcite and dolomite cementation, which completely or partially occluded pores. Cement types appear to be early isopachous calcite (i; C1-non-luminescence), equant (ii; C2-dull CL), fairly coarse secondary dolomite rhombs (iii; C3-zoning red CL), coarse sparry calcite (iv; C4-dull CL), and meteoric equant calcite (v; C5-bright orange CL & vi; C6-bright yellow CL). Fluid inclusion analyses invoked three distinct groups of fluids. Group 1 is reflected by fluids with equant calcite (C2) composition, characterized by Th values (126 °C) and salinity of 16 wt.% (NaCl equivalent), and they are interpreted as burial pore-waters. Group 2, which is represented by fluids associated to shallow burial dolomite cementation (C3), has Th values about (127 °C) and salinity of 17 wt.% (NaCl equivalent). The last group, i.e. coarse sparry calcite (C4), is occurred along fractures and vugs and characterized by high Th values (169 °C) and salinity of 17.5 wt.% (NaCl equivalent) which shows that fluids with a higher temperature migrated from deeper parts during deep burial. The hydrocarbon inclusions with yellow fluorescence can be observed in coarse calcite filling fractures in Dalan formation which shows that they are secondary, and hydrocarbon migration predates the precipitation of fracture filling cements.