 |
| Titel |
CO2 column height influenced by geothermal gradient in sedimentary basins of the USA |
| VerfasserIn |
Jacob Covault, William Craddock, Madalyn Blondes |
| Konferenz |
EGU General Assembly 2011
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250052673
|
|
|
|
|
|
| Zusammenfassung |
| One of the greatest risk factors in assessment of CO2 storage potential is seal integrity in a
spectrum of subsurface conditions. Secure storage of CO2 can be attained when
the capillary entry pressure of the sealing formation is greater than the buoyant
pressure of CO2 rising through water-filled pores. Maximum CO2 column height
is an important factor in buoyancy, but its prediction is difficult in frontier-basin
settings that lack context from oil and gas production. In such data-poor settings,
coarse-scale structural contour maps can indicate large structural traps containing porous
reservoirs several thousands of feet thick for potential CO2 storage. It is tantalizing to
include the entire volume of the trap in resource assessments, but would the potential
CO2 column height be too great for an overlying shale formation to effectively
seal?
Utilizing oil and gas industry techniques, we calculate a balance of capillary entry and
buoyant pressures for prospective CO2 reservoir seals and brine-supercritical CO2 mixtures
to evaluate depths at which seals can contain a given CO2 column height across the United
States. We vary the density of supercritical CO2 with depth according to hydrostatic
pressure and the regional geothermal gradient, vary pore-throat radius according to an
empirical relationship of exponentially diminishing radius with depth, and hold constant
other variables, including interfacial tension, contact angle, and brine density. The
results indicate that individual basins generally exhibit a nonlinear relationship of
increasing maximum CO2 column height with depth. Moreover, “cold” basins with
relatively low geothermal gradients, such as the Great Valley of California, which
was a Mesozoic-Cenozoic forearc basin prior to the evolution of California to a
transform continental margin, can sustain the same CO2 column heights at much
shallower depths than “hot” basins with higher geothermal gradients. This is because
supercritical CO2 is denser at given depths of “cold” basins and, as a result, less buoyant.
Results from a selection of sedimentary basins in the United States show that the
depths at which seals can support a given CO2 column height vary by as much as a
factor of 1.5 based on differences among geothermal gradients. For example, our
calculations predict that a maximum CO2 column height of 500 m is contained at  2 km
subsurface depth in the “cold” Great Valley, California (conservative geotherm of  12.5
°C/km), and at  3.5 km depth in the “hot” Green River Basin, Wyoming (maximum
geotherm of  40 °C/km). These insights have important implications for supercritical
CO2 sequestration assessments. A general understanding of regional tectonics that
impact the lithospheric geotherm can provide informed predictions of temperature
gradients and column height variability with depth in frontier sedimentary basins. |
|
|
|
|
|
|