AN INTEGRATED STUDY OF DIAGENESIS AND DEPOSITIONAL FACIES IN TIDAL SANDSTONES: HAWAZ FORMATION (MIDDLE ORDOVICIAN), MURZUQ BASIN, LIBYA

摘要

Studies of the impact of diagenesis on reservoir quality in tidal sandstones can be of great importance in successful hydrocarbon exploration. The study reported here shows that diagenetic alterations and bioturbation have induced considerable deterioration and heterogeneity in the reservoir quality of the sand-dominated tidal deposits of the Middle Ordovician Hawaz Formation in the Muruq Basin, Libya. Comparison is made between the diagenetic evolution of samples from the subsurface (present-day depth 1500 m) and from surface outcrops in order to study the impact of burial and uplift on the spatial and temporal distribution of reservoir quality in the Hawaz Formation sandstones. Eogenetic alterations, which were mediated by meteoric water circulation, included kaolinitization and dissolution of framework silicates and mechanical compaction. Mesogenetic alterations (T > 70°C; depth > 2 km) included pressure dissolution of quartz grains and concomitant quartz cementation, conversion of kaolinite into dickite, illitization of kaolinite and of grain