Fluids and Rocks - Introduction to Carbon Capture and Sequestration - page 385

Table 9.2.2 Typical properties of sandstone aquifers and
shale seals from the USA Gold Coast
Sandstone Shale

Porosity ( φ ) 0.15 to 0.35 0.06 to 0.15

Permeability High Low

Mineralogy

Quartz (vol. %) 58 19

Feldspars (vol. %) 28 10

Phyllosilicates (vol. %) 12 58

Carbonates (vol. %) 2 11

Organic matter (vol. %) 0 2

Typical values of the porosity φ and mineralogy in sandstone aqui-
fers and shale seals. The mineralogy data are representative of
sandstone-shale sequences from the USA's Gulf Coast. Data from
Xu et al. [9.1] .

were formed. This will provide some insight into how nature has provided
us with sites that are ideal for geological carbon sequestration.
Long-term tectonic processes acting on the earth's crust throughout
geological time have resulted in regions of large vertical uplift (mountains
and highlands) from which sediments are eroded and large vertical sub-
sidence (valleys and basins) in which sediments are deposited. These
processes have created thick sedimentary basins where vast volumes of
sedimentary rocks have formed.
The local conditions prevailing during sedimentation are referred to
as the depositional environment. Depositional environments over space
and time can be highly variable, ranging from vigorous fl uvial systems
(e.g., rivers), to gentle tidal systems (e.g., estuaries), to off-shore marine
environments (continental shelves, submarine canyons), to subaerial arid
and windy environments (alluvial fans and dunes). Coarse-grained sedi-
ments are formed during periods of high-energy water or wind transport,
while fi ne-grained sediments are formed by sedimentation from low-
energy fl uvial or marine systems.
Repeated cycles of climate and sea-level change during the fi lling of
sedimentary basins have resulted in periodic variations in the deposi-
tional environment such that recurring cycles of deposition of coarse