Influence of Quartz Cementation and Lithic Sand Grains on Porosity and Permeability in the Agbada Sandstones of the Rio Del Rey Basin, Cameroon
Victor Eseme
University of Port Harcourt, Nigeria
email: [email protected]
The Rio Del Rey Basin, a protrusion into Cameroon of the Niger Delta Complex is made of multiple north-south prograding, Late Miocene to Pliocene cycles. It is represented by three diachronous units which include, from bottom to top, the Akata Formation which is basically made of shale, the Agbada Formation which is a sandy unit interstratified with shale, and the Benin Formation which is predominantly sand. The Agbada Formation is considered to be very important throughout the basin as it hosts the main hydrocarbon reservoirs.
Reservoir quality is a critical parameter to the economics of any endeavour in oil and gas exploration and production. In this study detailed petrographic analysis and techniques of fluid inclusion geothermometry were combined with petrophysical data to investigate the controls of quartz cementation and lithic quartz grains on the reservoir quality of the Agbada Formation. A preliminary petrographic study shows that detrital grains are mostly made of quartz and lithic fragments with very minimal feldspar. The quartz particles are dominated by monocrystalline quartz, although there are appreciable amounts of polycrystalline quartz as well. Clay-rich ductile rock fragments constitute the lithic components. There is an increase in diagenetic quartz (quartz cement) with increasing burial depth. The presence of chlorite is also common , forming isopachous coatings on quartz grains which appear to predate quartz cement.
There is a remarkable loss of porosity with increasing burial depth which can be related to the already documented increase in the occurrence of quartz cement with depth. But the actual role which lithic grains and diagenetic quartz play in influencing porosity and permeability will be found by the end of the study.
AAPG Search and Discovery Article #90033©2004 AAPG Foundation Grants-in-Aid