Pakistan Journal of Geology (PJG)

In this study integrated approaches combining field study, petrographic analysis and petrophysical analysis has been used to infer the depositional and diagenetic effects on reservoir characteristics. The exposed stratigraphic section of Chorgali Formation at its type locality was logged, sampled and petrophysical analysis of well log data from Fimkassar-02 were carried out. Three microfacies recognized from petrographic studies are: Bioclastic Wackestone-Packstone Microfacies, Mixed Bioclastuc Wackestone-Packstone Microfacies and Larger Foraminiferal Wackestone-Packstone Microfacies. The depositional texture and faunal association suggested that the microfacies represents deposition in a low energy, distally steepened ramp type of setting. Due to the deposition in low energy environment the ratio of lime mud is more than bioclasts as a result the primary pore spaces in the formation are negligible. The analysis further showed that the carbonates of Chorgali Formation was also subjected to various diagenetic changes, mainly showing the compaction, stylolitization, aragonite to calcite transformation (neomorphism), tectonically induced fracturing and calcite veins passing from marine diagenesis to meteoric diagenesis through burial diagenesis. Fracturing due to later tectonic deformation have had a major influence on porosity generation and in some cases fracturing and stylolites together have had an important effect on permeability values. The petrophysical analysis shows that the Eocene Chorgali Formation is very good reservoir with average hydrocarbon saturation of 80 %.