Large-Scale Geological Carbon Sequestration - Introduction to Carbon Capture and Sequestration - page 487

CO 2 Injection Well

Groundwater
Quality Changes

Groundwater
Wells

Aquifer

Drinking Water
Aquifer

Leakage of CO 2
Through Faults of Wells

CO 2 Storage Formation

Injection of
Supercritical CO 2

Figure 10.4.2 Potential CO 2 leakage
Sketch of potential leakage process for CO 2 or deep brine to impact potable ground-
water. Figure redrawn from Apps et al. [10.38].

Earthquakes occur across an enormous range of magnitudes as indi-
cated by the logarithmic scale used to describe them (the Richter scale).
In addition, there is a long-recognized inverse logarithmic relationship
between earthquake magnitude and frequency known as the Gutenberg-
Richter Law. In short, it is very likely that a very small earthquake will
occur and very unlikely that a large earthquake will occur, regardless of
cause. Small earthquakes at depths greater than 2 km, e.g., those with
Richter-scale magnitudes up to 2 or so, cannot be felt at the ground
surface.
Earthquakes occur naturally along faults due to tectonic forces.
Briefl y, tectonic stress builds in the rock which resists deformation
(strain) due to its inherent strength. Eventually the strength of the rock as
controlled by its weakest elements, faults and fault zones, is overcome
and slip occurs to relieve the stress. The slip event can produce seismic
waves that travel great distances and change in amplitude depending on
the type of rock through which they are traveling: this is the earthquake.