Petrography and geochemistry of sandstone samples of Vischkuil formation, Karoo Supergroup, South Africa

Abstract

Petrography and geochemistry of sandstones of Vischkuil formation in the Ecca Group of the Karoo Supergroup of South Africa was investigated to evaluate the petroleum potential of its reservoir rock. The petrographic analysis showed that the sandstones were poorly to moderately sorted with evidence of angular to sub-angular grains. The sandstones are lithic arenite. Diagenetic processes on the sandstone include physical and chemical compaction as seen from the straight grain contacts and dissolution of the quartz grains. There is an evidence of pore space reduction by the rearrangement and cementation by silica, calcite and clay minerals. The petrographic analysis also revealed that there is dominance of monocrystalline quartz grains and evidence of cratonic setting derivation. The chemical alteration index ranged from 52.96 to 65.5 %, an indication of a moderate weathering at the source area before deposition. The samples are texturally immature, which indicate poor storage capacity for fluids.