Description:
Northeastern Arizona encompasses the southwestern
part of the Colorado Plateau, an area of gently dipping
to slightly tilted Paleozoic and Mesozoic strata that
include porous and permeable sandstone units. The
Lower Permian Cedar Mesa Sandstone was identified
for study as a potential target for CO2 sequestration
in order to reduce anthropogenic CO2 emissions
to the atmosphere. The Cedar Mesa Sandstone is
overlain by the impermeable Organ Rock Formation,
which is necessary to prevent escape of sequestered
CO2. The salinity of groundwater in the Cedar Mesa
Sandstone is unknown, but must be determined before
CO2 can be sequestered because CO2 sequestration is
not permitted in potable groundwater under current
regulatory conditions. Well logs for 755 drill holes
were used to evaluate the extent, depth, and thickness
of subsurface formations. ESRI® ArcMap™ software
was then used to calculate the volume of the Cedar
Mesa Sandstone where the top of the unit is below
3000 feet (915 meters) depth, which is the minimum
depth necessary for CO2 sequestration where the CO2
is under sufficient pressure to remain in a dense, nearliquid
state. Well logs were used to evaluate porosity,
which was then used to calculate the amount of pore
space that is theoretically available for CO2 storage
(the effective porosity). We calculate that there are
between 30 km3 and 80 km3 of pore space in the Cedar
Mesa Sandstone. The fraction of pore-space volume
that is accessible to CO2 injection is estimated to be
approximately 0.5% to 5%. Applying this storage
efficiency to the Cedar Mesa Sandstone indicates
that 0.15 km3 to 4.3 km3 of pore space is accessible
to injected CO2, and that 0.114 to 3.24 billion tonnes
of CO2 could be sequestered in this pore space at a
density of approximately 750 kg/m3.