Petrophysical evaluation and characterization of sandstone reservoirs of the western Bredasdorp Basin, South Africa for well D-D1 and E-AP1
The Bredasdorp Basin was formed consequent to extensional episodes during the initial stages of rifting in the Jurassic age. The basin acted as a local depocentre and was primarily infilled with late Jurassic and early Cretaceous shallow-marine and continental sediments. Two wells namely; D-D1 and E-AP1 were studied in order to evaluate the petrophysics and characterize sandstone reservoirs of the western Bredasdorp basin. This could be achieved by generating and comparing results from core analysis and wireline in order to determine if the two wells are comprised of good quality sandstone reservoirs and if the identified reservoirs produce hydrocarbons. A number of methods were employed in order to characterise and evaluate sandstone reservoir, these included; editing and normalization of raw wireline log data ,classification of lithofacies on the basis of lithology, sedimentary structures, facies distribution, grain size variation, sorting of grains, fossils and bioturbation; calibration of log and core data to determine parameters for petrophysical interpretation; volume of clay; determination of porosity, permeability and fluid saturation, cut-off determination to distinguish between pay and non-pay sands. Borehole D-D1 is located in the western part of the Bredasdorp Basin. Only two reservoirs in well D-D1 indicated to have pay parameters with an average porosity ranging from 11.3% to 16%, average saturation from 0.6% to 21.5% and an volume of clay from 26.5% to 31.5%. This well was abandoned due to poor oil shows according to the geological well completion report. On the contrary well E-AP1 situated in the northwestern section of the basin showed good quality reservoir sandstones occurring in the 19082m to 26963m intervals though predominantly water saturated. Pay parameters for all five reservoirs in this well showed zero or no average porosity, saturation and volume of clay.