An integrated approach to evaluate dolomite in the Eocene Chorgali Formation, Khair-e-Murat Range, Pakistan: Implications for reservoir geology
Keywords:
Chorgali Formation, Dolomite, Scanning electron microscopy, Energy dispersive x-ray spectroscopy, X-ray diffraction, Chemical staining, Khair-e-Murat RangeAbstract
An integrated approach has been deployed to investigate dolomite of the Eocene Chorgali Formation exposed in the Khair-e-Murat Range, Potwar Plateau, Pakistan. Two typical genetic dolomite groups are identified and interpreted based on X-rays Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), chemical alizarin red staining and petrographic studies. The first group is represented by early-diagenetic alizarin-red-unstained dolomites. They are associated with evaporite(s) (gypsum) and characterized by stoichiometric composition of 50.28 mole % CaCO3 and degree of order is 0.682. The second group includes fine crystalline, alizarin-red-unstained relatively early late or late diagenetic dolomite crystals not associated with evaporite(s). It is represented by nearly stoichiometric composition of 48.76 mole % CaCO3 and degree of order varies from 0.58 to 0.9747. The dolomite associated with evaporite (gypsum) is interpreted to be precipitated in arid peritidal (sabkha) environment while the other dolomite not associated with evaporite is reflecting dolomitization in open diagenetic system (mixed marine-meteoric environment). Within the Chorgali Formation, the presence of dolomite is enhancing the reservoir capability making it prospective for hydrocarbon exploration. The photomicrographs based estimated porosity values are 2.0 % and 1.0% for dolomite associated with evaporite(s) and dolomite-not- associated with evaporite(s) respectively, however, qualitative permeability seems to be relatively higher in dolomite associated with evaporite(s).
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