AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Assessing the Relationship Between Aeolian Bedforms and Hydraulic Properties in the Jurassic Navajo Sandstone in Central Utah for the Evaluation of CO2 Sequestration
(1) Energy and Geoscience Institute, University of Utah, Salt Lake City, UT.
The anthropogenic origin of global climate change via increased CO2 emissions into the atmosphere is the general consensus by the scientific community and CO2 sequestration (long-term storage within the subsurface) has been proposed as an option for mitigating the effects of this greenhouse gas. Reliable and long-term CO2 storage requires a porous, saline aquifer, such as the Navajo Sandstone in central Utah, for viable CO2 sequestration. Geometric patterns of aeolian bedforms and petrophysical data (hydraulic properties) were mapped through the upper portion of the Navajo Sandstone in order to evaluate it for CO2 sequestration. 3D reconstructions of aeolian depositional facies and bedform geometries demonstrate a wide variety of dune types in the Navajo Sandstones. By mapping the angle and direction of bounding surfaces and internal erosional surfaces within the cosets, several dune types were recorded. Both simple large dunes and compound dunes, which preserve smaller superimposed dunes migrating along lee slopes of larger dunes, were recognized and mapped. Bounding surfaces range from subhorizontal 1st order surfaces to steeply dipping reactivation surfaces generated from shifting wind direction, superimposed dunes or migration of scour-pits located at the base of the lee slope. Finer-grained wind ripple laminations line 1st and 2nd order bounding surfaces and are found up to 50 cm thick. Well-sorted, medium-grained sandstones composed of grain flow sediments occupy the majority of the sediments between bounding surfaces. Laboratory measurements suggest that porosity measurements can range up to 5 fold between wind ripple and grain flow facies. Measurements collected in the field demonstrate that permeability ranges significantly as well. Variations in hydraulic properties mimic shifts in facies along bounding surfaces. Bounding surface geometries range from subhorizontal to sinuous in 2D and 3D and act as baffles within the Navajo Sandstone reservoir. Bedform reconstructions, geometries and hydraulic properties collected from the outcrop act as inputs for geostatistical and, in turn, fluid flow models of CO2 migration. Preliminary modeling of 2D CO2 migration through sinuous cross-bedding bounding surfaces suggests that these baffles influence the amount of CO2 stored as well as its direction of migration and migration pathways. These models enable predictions of potential CO2 sequestration sites and potential areas with inefficient storage capacity.