Tectonic significance of porosity and permeability regimes in the red beds formations of the South Georgia Rift Basin

Abstract

A simple, new porosity/permeability-depth profile was developed from available laboratory measurements on Triassic sedimentary red beds (sandstone) from parts of the South Georgia Rift (SGR) basin in order to investigate the feasibility for long-term CO2 storage. The study locations were: Sumter, Berkeley, Dunbarton, Clubhouse Crossroad-3 (CC-3) and Norris Lightsey wells.As expected, both porosity and permeability show changes with depth at the regional scale that was much greater than at local scale. The significant changes in porosity and permeability with depth suggest a highly compacted, deformed basin, and potentially, a history of uplift and erosion. The permeability is generally low both at shallow (less than 1826 ft/556.56 m) and deeper depths (greater than 1826 ft/556.56 m). Both porosity and permeability follow the normal trend, decreasing linearly with depth for most parts of the study locations with the exception of the Norris Lightsey well. A petrophysical study on a suite of well logs penetrating the Norris Lightsey red beds at depths sampled by the core-derived laboratory measurements shows an abnormal shift (by 50%) in the acoustic travel time and/or in the sonic-derived P-wave velocity that indicates possible faulting or fracturing at depth. The departure of the Norris Lightsey's porosities and permeabilities from the normal compaction trend may be a consequence of the existence of a fault/fracture controlled abnormal pressure condition at depth. The linear and nonlinear behaviors of the porosity/permeability distribution throughout the basin imply the composition of the SGR red beds, and by extension analog/similar Triassic-Jurassic formations within the Eastern North American Margin has been altered by compaction, uplift, erosion and possible faulting that have shaped the evolution of these Triassic formations following the major phase of rifting.

New insights into lithology and hydrogeology of the northern Newark Rift Basin

“…These results suggest finer‐grained lacustrine strata may have superior reservoir properties to the coarse‐grained fluvial sandstones due to better sorting, and that in the Newark basin, reservoir properties of the finer‐grained lacustrine formations should also be evaluated. Furthermore, a separate study focused on tectonic regimes in the SGR basin suggested that those high porosity‐permeability lacustrine samples came from a structural block with distinctly different tectonic history, potentially separated from the rest of the basin by a system of faults [ Akintunde et al ., ]. Intrabasin faults are also common in the Newark Basin, especially in the central and southern parts [e.g., Schlische , ].…”

“…In the South Georgia Rift (SGR), another rift basin on the eastern North American margin evaluated for its CO 2 storage potential, laboratory analysis of porosity and permeably on about a dozen core plugs and sidewall cores is available [Akintunde et al, 2014[Akintunde et al, , 2013. The data suggest that coarse fluvial sandstones have medium to low matrix porosity (2-15%) and low permeability (10 23 210 21 mD), attributed to poor sorting, high angularity and small pore throats [Akintunde et al, 2013].…”

“…As a part of concentrated effort by the U.S. Department of Energy (DOE) in partnerships with major private and state organizations, multiple sedimentary basins throughout the country are being assessed for CO 2 storage potential [e.g., Rodosta et al ., ; Litynski et al ., ]. On the eastern North American margin they include the onshore Mesozoic Newark Rift Basin and offshore South Georgia Rift Basin, thought to be the largest on this margin but buried below the Cretaceous‐Cenozoic Coastal Plain sediments of South Caroline, Georgia, Alabama and Florida [ Akintunde et al ., ]. The advantages of Newark basin include its proximity to many CO 2 emitters [e.g., Goldberg et al ., ; Tymchak et al ., ], easy accessibility, and significant amount of information about the basin accumulated in prior studies, which included studies of field outcrops [e.g., Olsen , ; Cornet and Olsen , ], core holes [e.g., Kent et al ., ; Olsen et al ., ; Reynolds , ], and seismic‐reflection surveys [ Costain and Coruh , ; Reynolds , ; Withjack et al ., ].…”

A Novel Modeling Approach to Stochastically Evaluate the Impact of Pore Network Geometry, Chemistry and Topology on Fluid Transport

“…In addition to connectivity, other materials properties are important in this quest, for example, the porosity of a medium, defined as the volume fraction of its voids (Thakur 2017). Porosity affects permeability so strongly (Akintunde et al 2014;Akinlotan 2016) that Archie proposed a porosity-permeability relationship, derived for sandstones, limestones and muddy sands, which predicts a tenfold increase in permeability when porosity increases by merely 3% (Archie 1950). Because it has been suggested that porosity intrinsically depends on the microstructure of porous materials (Shen et al 2018), we performed a sensitivity analysis on the effect of macro-and microporosity on permeability (Apostolopoulou et al 2019).…”

Classification of Red-Bed Rock Mass Structures and Slope Failure Modes in South China

“…The mechanical properties of red-bed soft rock containing weak interlayers can be studied by laboratory and field analyses of the mineralogical composition of the weak interlayer [24,25]. Structural features such as faults, joints, interlayer slippage zones, and pelletization dissection are usually well developed and are considered to be other types of main structure plane in red beds, such as the interlayer slippage zone (a structurally related feature) of red beds located in southwestern China [26] and faults or fractures at the depth of red beds in the South Georgia Rift (SGR) basin [27]. It is well known that rock mass structures play a dominant role in the stability of a rock mass [11,16,28].…”