Print this pageDepositional Facies, Diagenesis and Their Impact from the Reservoir Quality of the Lower Cretaceous Sandstone, Orange Basin, Offshore, South Africa
Orange basin was formed during the late Jurassic to early Cretaceous periods due to Gondwana breakup and rifting and later drifting apart of the African and South American plates. It is vital to understand that the basin consists of siliciclastic sandstone which took its sediment supply from river system with a rivalling delta to the north of the basin. The Albian age sandstones of the Ibhubesi oil field area is an important oil exploration target in the Orange Basin, South Africa. This study deals with the Albian age of the Cretaceous period, which was deposited in a fluvial/deltaic system. The complexities in the depositional environment have made this study to be highly imperative.
Core description, petrographic studies which includes thin section, X-ray diffractometry and scanning electron microscopy, geochemical studies involving XRF, FTIR and pore water chemistry (pH, EC and TDS) were used for proper understanding of the complexities of the mineralogical characteristics of the reservoir intervals obtained from the interpretation of the different wireline logs used (GR, DT, HCAL, NPHI, RHOB and Resistivity logs).
Four major depositional microfacies were identified consisting of interdistributary bay, front bar, meandering channel system and storm dominated shelves. Each of the analysed well has more than one reservoir sand of considerable thickness; fall within the Low System Tract and also with a relatively fair to good porosity and permeability. Chlorite, illite, kaolinite and albite were the major authigenic minerals affecting the reservoir quality in the area.
AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil