Porosity and Permeability of the Red Beds Formation of the South Georgia Rift Basin: Implications for CO2 Storage
Olusoga Martins Akintunde, Camelia C. Knapp, and James H. Knapp
University of South Carolina, Department of Earth and Ocean Sciences, Columbia, South Carolina, United States of America
A key consideration for CO2 sequestration site selection is the ability to demonstrate the presence of a porous reservoir with adequate storage capacity. In addition, subsurface suitability for CO2 storage will depend on reservoir injectivity and seal integrity that are both closely related to rock properties such as porosity and permeability. Results of petrophysical and experimental studies carried out on the red beds formation within the South Georgia Rift basin show that these continental rift deposits, that are capped by basalts and/or diabase sills, has confined porous units capable of storing 3.73 to 13.23 billion tones of CO2. Reservoir thickness of about 420 m and an average porosity of 14% were obtained. Results also show that the South Georgia Rift basin manifests distinct porosity-permeability regimes that are influenced by the depositional environments. These are: (1) high-porosity, low/medium permeability zone; (2) medium/low porosity, low permeability zone; (3) low porosity, low permeability zone, and, extremely low porosity and low permeability zone. The high-porosity, low/medium permeability zone is associated with lacustrine deposits and consists of fine-grained Triassic sandstones with interbedded layers of siltstone and mudstone. The medium/low porosity, low permeability zone is dominated by fluvial fine-to very fine-grained sandstone, while the extremely low porosity and permeability zone are characterized by fluvial and alluvial-fan deposits. The presence of low permeability red beds is a prominent occurrence within the basin. This characteristic, which is substantiated by physical examination of cores and analysis of thin section, is caused by poor sorting and small pore throats.
AAPG Search and Discovery Article #90157©2012 AAPG Foundation 2012 Grants-in-Aid Projects