Reservoir Quality Analysis: Case Study of the Orange Basin, Offshore South Africa

Abstract

Located offshore the west coast of South Africa, the Orange Basin has been demonstrated to offer excellent opportunities for hydrocarbon exploration. This study incorporated an array of data to maximize the understanding of Cretaceous siliciclastic reservoirs that characterize the basin. In order to have a comprehensive perceptive of the basin geology, three dimensional models of porosity, water saturation, permeability and petrophysical information arriving from well-logs were amalgamated with subsurface seismic data and used as the basis for this study. Three key intervals were identified in the reservoir and were critically examined by differences in granulometry (fine- to coarse-grained sandstones), with increased heterogeneity spatially noted from the shelf to the slope areas. The sandstone units exhibit porosities and permeabilities ranging from 0.1 to 6.8% and 0.002 to 5.30 mD on the shelf area, respectively, whereas the same parameters range from 4 to 16% and 0.17 to 4 mD in the slope. Petrographic studies reveal poor to moderately crystalline kaolinite verms, locally illitised, which block pore throats in some of the reservoir intervals. A notable increase in chlorite, smectite and illite was identified in the reservoirs located on the slope area. Storage and flow capacity reveals that well AK1 (situated in the slope) contains the highest storage and flow capacities, while well KE1 (deep-water area) shows the least amount of storage and flow capabilities. Therefore, this study has identified that reservoirs found within the middle of the slope offer higher porosity, permeability even though quartz cementation has a notable increase in these reservoirs.

AAPG Datapages/Search and Discovery Article #90332 © 2018 AAPG International Conference and Exhibition, Cape Town, South Africa, November 4-11, 2018