Fluids and Rocks - Introduction to Carbon Capture and Sequestration - page 391

Porosity

The volume fraction of a rock that is occupied by pore space is known
as the porosity ( ). The clastic sedimentary rocks provide abundant

intergranular pore space, i.e., the void space located between solid
grains. This pore space is highly irregular with very narrow channels, say
on the order of 10-100 microns, between grains, referred to as pore
throats, and larger openings or cavities, say on the order of hundreds of
microns, referred to as pore bodies. The image in Figure 9.2.6 is a 3D
microtomographic image of the pore space of a sandstone sample from
the Frio Formation (Texas Gulf Coast) showing the complex nature of
pore throats and pore bodies. The right-hand image of Figure 9.2.6 is the
corresponding skeleton (solid material) of the rock [9.8].
Intergranular pores are commonly well-connected through pore
throats. These connections allow fl uids (gasses and/or liquids) to fl ow
throughout the pore space as driven by gravitational or pressure forces.
This permeability is necessary for sequestration in order to allow injection
of CO 2 and widespread storage throughout the formation using a fi nite
number of wells.

φ

Figure 9.2.6 Sandstone pore space
Actual sandstone pore space shown by the solid gold color (left) and the corresponding
skeleton (rock grains) (right) constructed by application of synchrotron microtomography
methods at the Advanced Light Source [9.8]. Each side of the cube is 0.9 mm in length.
Image reproduced with permission from Springer Science + Business Media [9.8, Figure 5].