posted on 2015-10-13, 00:00authored byIan C. Bourg
Fine-grained sedimentary rocks (shale
and mudstone) play important
roles in global CO2 abatement efforts through their uses
in carbon capture and storage (CCS), radioactive waste storage, and
shale gas extraction. These different technologies, however, rely
on seemingly conflicting premises regarding the sealing properties
of shale and mudstone, suggesting that those rocks that lend themselves
to hydrocarbon extraction may not be optimal seals for CCS or radioactive
waste storage, and vice versa. In this paper, a compilation of experimental
data on the properties of well-characterized shale and mudstone formations
is used to demonstrate that clay mineral mass fraction, Xclay, is a very important variable the controls key material
properties of these formations and that a remarkably sharp threshold
at Xclay ∼ 1/3 separates fine-grained rocks with very different properties. This
threshold coincides with the predictions of a simple conceptual model
of the microstructure of sedimentary rocks and is reflected in the
uses of shale and mudstone formations for CCS, radioactive waste storage,
and shale gas extraction.