Geologic Storage of CO~2~: Potential Environmental & Human Health
Effects

**Problem**: The carbon cycle is dominated by reactions that involve
carbon dioxide (CO2). The geologically rapid exchange of carbon among
the various reservoirs tends to stabilize the carbon cycle and to
prevent reservoirs from getting out of balance. However, anthropogenic
activity and the burning of fossil fuel have caused a continuous and
dramatic increase of atmospheric CO~2~ over the past 120 years. The role
of CO~2~ as a greenhouse gas and its potential effect on global climate
have been well documented. Power plants are a major source of this
excess CO~2~ and although the capture of CO~2~ is a proven technology,
its disposal and storage remain problematic. There are major
uncertainties involving the environmental impact and long-term storage
associated with the disposal of CO~2~ in deep aquifers, in shallow or
deep oceans including hydrates, in depleted oil and gas reservoirs, salt
domes, and in deep coal seams. To date, research on the geologic storage
of CO~2~ has focused primarily on storage feasibility and reservoir
capacity and integrity. But, in addition to keeping CO~2~ contained in
the subsurface, there is growing concern about the potential
contamination of groundwater resources and municipal aquifers with heavy
metals and toxic organic compounds released by the interaction of CO~2~
with formation fluids and rocks. Liquid CO~2~ is a very effective
organic solvent for polycyclic aromatic and other hydrocarbons, many of
which are known carcinogens. Aqueous CO~2~ is acidic and capable of
dissolving mineral phases. Potential leakage pathways include capillary
entry pressure, chemical corrosion and dissolution, microbially-mediated
conversion of CO~2~ to CH~4~ as well as faults and fractures and
borehole corrosion.

**Objectives:** The objectives are to 1) explore the fundamental
chemical reactions between CO~2~ saturated fluids and liquid CO~2~ and
potential reservoir fluids and rocks, 2) explore and understand the
risks and hazards associated with geologic storage 3) identify favorable
and unfavorable disposal and storage conditions 4) provide guidance for
site characterization and monitoring.

**Work strategy:** We propose 1) to carry out a systematic experimental
study to react liquid CO~2~ and CO~2~ saturated fluids with a variety of
aquifer fluid compositions and rock types over a wide range of
temperature and pressure to identify the extent and type of chemical
reactions that occur to resolve some of the uncertainty involving the
disposal of CO~2~, 2) to identify rock types that might provide for the
irreversible fixation of CO~2~ as a solid phase carbonate, 3) to
identify rock and reservoir type and environmental conditions most
likely to release environmental contaminants, and 4) to determine cap
rocks best and ill suited for seal integrity to retain liquid CO~2~ and
dissolved contaminants.

**Relevance:** The proposed work will provide information necessary for
addressing science strategic goals of the USGS science plan regarding
public health effects from environmental contamination and climate
change. An understanding of the geochemical reactions that are likely to
occur in the subsurface will help industrial managers design appropriate
pilot experiments and production scale operations in geologically
optimal areas and help alleviate public concern.

**Collaborators:** USGS WRD; USGS Energy; DOE, Industry; National Labs;
Health Science Community

**Technology:** Unique experimental capability