Abstract:
The early Eocene Habib Rahi Limestone of the North Waziristan, Sulaiman Basin
has been studied for microfacies analysis, depositional model, diagenesis, and reservoir
potential.This study is mainly focused on investigating and assessing reservoir quality
using depositional and diagenetic processes. The Formation is composed of medium to
thick-bedded, hard, highly fossiliferous, fractured limestone with interbedded shale and
marls. Five microfacies have been identified based on the relative estimated ratio of
allochems constituents and micrite. These microfacies are Mudstone, Wackstone, WackPackstone, Packstone, and Peloidal Grainstone and comprises larger benthic forams such
as Nummulites, Assilina, Alveolina, Milliolids, Lockhartia, Orbitolites, and green algae.
Based on mineral composition, fossil assemblages, and micritic matrix, the depositional
environment for the Habib Rahi Limestone is interpreted as proximal inner ramp to distal
middle ramp environment. The diagenetic processes observed in this study include
micritization, cementation, dissolution, neomorphism, pyritization, mechanical and
chemical compaction, stylolitization, sparitization, fracturing, and veins. The depositional,
diagenetic, and deformation processes are the controlling factors of the distribution of
porosity and permeability. The primary reservoir characteristics of this formation are
highly affected by diagenetic processes developing it into a productive reservoir. Fracture
and dissolution are significant mechanisms that increased the reservoir potential of the
Habib Rahi Limestone at both the microscopic and macroscopic levels. In the studied
section, the visually estimated average micro porosities of the Habib Rahi Limestone range
from 0.5 to 2.1%. Intergranular porosity, dissolution porosity, moldic porosity, and fracture
porosity are among the recognized porosity types.
