Integration of Petrographic and Petrophysical Analyses to Characterize Reservoir Quality of Lower Cretaceous Sediments in the Orange Basin, Offshore South Africa

Abstract

Commercial hydrocarbon production relies on porosity and permeability which is crucial for the storage and flow capacity estimation of the reservoirs. Petrographic and Petrophysical studies over the years has proven to be a reliable approach to assess the quality of the reservoirs. It is upon this basis that a need arises to integrate petrographic and petrophysical well data to study in detail the impact of the clay diagenesis on the quality of the selected sandstone reservoirs. Thus, this study gives first-hand information about the reservoir quality for hydrocarbon producibility. Five wells were studied and sandstone reservoirs were identified from wireline log curves. Eighty three (83) sandstone samples were collected from these reservoirs for petrographic analyses within Hauterevian to Cenomanian sequences. Thin section analyses revealed pore restriction by quartz and feldspar overgrowths and pore filling by siderite, pyrite, kaolinite, illite, chlorite and calcite. These diagenetic minerals occurrence has reduced intergranular pore space to almost no point count porosity in well K-A2 whilst in A-J1, A-D1, A-H1 and A-K1 porosity increases at some zones due to secondary porosity. Volume of clay, porosity, water saturation, permeability, storage capacity, flow capacity and hydrocarbon volume were calculated within the reservoir interval. The average volume of clay ranged from 6% to 70.5%. The estimated average effective porosity ranged from 10% to 20%. The average water saturation ranged from 21.7% to 53.4%. Permeability ranged from a negligible value to 411.05mD. Storage capacity ranged from 6.56 scf to 2228.17 scf. Flow capacity ranged from 1.70 mD-ft to 31615.82 mD-ft. Good to very good reservoir qualities were observed in some zones of well A-J1, A-K1 and A-H1 whereas well A-D1 and K-A2 presented poor qualities. Well K-A2 is thus recommended for reservoir stimulation to increase capacity.

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