Secure, long-term geological carbon sequestration in mafic igneous rocks
Sequestration of CO2 generated by power plants by injection into deep aquifers (geological sequestration) has been proposed as a possible alternative for the reduction of excessive greenhouse gases in the atmosphere. For a long-term geological sequestration of CO2 solid end products such as (Ca,Mg)CO3 are desirable due to their chemical stability, non-toxic nature and lack of fluidity for rapid migration. Our hypothesis is that aquifers associated with mafic igneous rocks are good canditates for sequestering CO2, presumed that the geological and hydrogeological conditions are suitable for high pressure CO2 injections. When high pressure CO2 is injected into deep aquifersm it will acidify the groundwater. This acid may be neutralized by reactions with the surrounding mafic rocks. These reactions can be represented by (Takahashi et al., 2000):
Mg2SiO4 + 2CO2 => 2MgCO3 + SiO2
CaAl2Si2O8 + CO2 + H2O + SiO2 => CaCO3 + Al2Si4O10(OH)2
Under high CO2 pressure these reactions may be driven to the right to form carbonates. The feasiblity of this concept is tested with field and laboratory experiments.
In order to test the sequestration capacity of an aquifer system, hydraulic parameters such as effective porosity and permeability are required. An extended site characterization including borehole logging, pumping and injection tests, fluid sampling and fluid logging is conducted in two wells drilled through the Palisades diabase sill and into the underlying Triassic sediments of the Newark Basin. The wells are, which are located on the Lamont-Doherty Observatory campus, are approximately 450 m apart. Well-2 is 229 m and Well-3 305 m deep.
Besides standard logging (caliper, natural gamma, resistivity (fluid and rock), neutron porosity and temperature logs) acoustic BHTV logs were used to digitally record the orientation and magnitude of dip of fractures intersecting the boreholes. Apparent fracture apertures were also estimated from the BHTV data.