Environmental Engineering Reference
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leakage from the intended target formation may cause an economic
impact by mixing with the oil or natural gas, but it is not considered an
HSE impact. Similarly, brine displacement from one deep aquifer to
another may change the salinity of the brine formations, but as long as
all of the deep aquifers are fi lled with non-potable water, such changes
do not impact HSE. We also point out that displacement of brine due to
CO 2 injection is not necessarily a leakage-related impact. As for induced
seismicity, the overwhelming majority of induced deep earthquakes will
be so small that they will have minimal HSE impact. The situation
becomes more controversial if earthquakes are felt by humans.
The shallower HSE impacts shown in Figure 10.4.1 are all related to
leakage of CO 2 out of its intended storage formation. Such leakage could
occur through wells or through certain kinds of faults and fractures (see
Section 9.6). A great deal of research is being carried out to evaluate the
potential for faults and wells to leak. In HSE risk assessment, we defi ne
risk as the likelihood of a leakage event leading to an impact on HSE
root zone effect
intrusion into vadose zone
intrusion into potable aquifers
intrusion into hydrocarbon reservoirs
displacement of brine
induced seismicity
Increasing Health, Sa fety, and Enviromental impact
Figure 10.4.1 Potential environmental impacts of geological carbon sequestration
Qualitative categorization of potential environmental impacts in terms of depth (vertical
axis) and HSE impact (horizontal axis). The vertical axis is not to scale, but the outlined
area highlights the impacts that potentially might occur at shallow depths. Figure
adapted from Oldenburg [10.37] .
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