Relating petrophysical parameters to petrographic interpretations in carbonates of the Chorgali Formation, Potwar Plateau, Pakistan

An integrated approach was deployed to relate the petrographical and petrophysical parameters of the Chorgali Formation to assess its reservoir potential. The petrographical study of the Chorgali Formation, exposed in Khair-e-Murat Range, disclosed that the original texture and composition are affected by diagenetic events (i.e. micritization, dolomitization, microfractures, stylolitization, compaction, dissolution, neomorphism and cementation). Of these, dissolution, dolomitization and microfractures enhanced reservoir quality, while micritization, compaction, neomorphism and cementation reduced reservoir suitability. Micritization occurred in marine phreatic conditions; dolomitization existed in the marine-meteoric mixing environment; dissolution, neomorphism and cementation took place in meteoric conditions. The mechanical and chemical compaction occurred in a burial diagenetic environment. In addition, the relationship among formation resistivity factor (F), compressional wave velocity (V_p) and porosity (ɸ) was also validated for the Eocene Chorgali Formation of Meyal Oil Field, Potwar Plateau, Pakistan. There is an inverse relationship between ɸ and F, V_p, however, the relation between F and V_p is directly proportional. Such inter-relationships assist in determining and interpreting the geological processes based on petrophysical parameters (ɸ, F and V_p). F and V_p may be high due to cementation, compaction, sealed fractures and lack of deformation in carbonates. On the other hand, F and V_p may be low due to dissolution, dolomitization, vacant fractures, lack of compaction and cementation. Similarly, ɸ is enhanced by processes lowering F and V_p and reduced by processes increasing F and V_p. Hence the diagenetic processes enhancing and reducing the porosity influence the electric and elastic properties of the carbonate rocks.