Structural Analysis of CO2 Leakage Through the Salt Wash and Little Grand Wash Faults from Natural Reservoirs in the Colorado Plateau, Southeastern Utah

Author

Anthony P. Williams, Utah State University

Date of Award:

5-2004

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Geosciences

Department name when degree awarded

Geology

Committee Chair(s)

James P. Evans

Committee

James P. Evans

Committee

Zoe Shipton

Committee

Thomas E. Lachmar

Abstract

The Little Grand Wash fault and the Salt Wash Graben in the Colorado Plateau of southeastern Utah emit CO₂ gas from abandoned drillholes, springs, and a hydrocarbon seep. Similar CO₂-charged water has also been emitted in the past, as shown by large localized travertine deposits and veins along and near the fault traces. The faults cut natural CO₂ reservoirs and provide an excellent analog for geologic CO₂ sequestration. The faults cut a north-plunging anticline of rocks consisting of siltstones, shales, and sandstones from the Permian Cutler Formation through the Cretaceous Mancos Shale. The Little Grand Wash fault has 260 m of throw and the stratigraphic separation across the Salt Wash Graben is 50 m. The fault rocks in the damage zone show hundreds of fractures, which decrease in density farther away from the faults. In specific areas, fractures with the presence of calcite mineralization indicate fluid migration and bleach zones from a few millimeters to 30 cm. This is evidence of past fluid migration directly associated with the fault zone. Calcite mineralization fills these fractures and is also deposited in a variety of other bed forms. Foliated fault gouge, 5 to 20 cm thick, forms clay smear structures with a scaly shear fabric in a zone 10 to 15 cm thick is seen in the fault core. The leakage is constrained to the footwalls of the northernmost faults throughout the area. Clay-rich gouge structures should be effective barriers to cross-fault flow. Well log, surface geologic, and geochemical data indicate that the CO₂ reservoirs have been cut by the faults at depth, providing a conduit for the vertical migration of CO₂ to the surface, but not for horizontal flow across the fault plane. Even though lateral cross-fault migration may be impeded, this study clearly indicates that there are possible migration pathways for the escape of CO₂ from faulted subsurface aquifers, including aquifers faulted by "low-permeability" faults with clay gouge. Three-dimensional flow models show how the fault's maximum permeability in the damage zone is parallel to the faults, and the leakage though the damage zone is localized near the fold axis of the regional anticline. Direct dating of the clay in the fault gouge was done by ExxonMobil with ⁴⁰Ar/³⁹Ar methods, indicating that fault movement occurred between the middle Eocene and the end of the Miocene. During this time, the Colorado Plateau is interpreted to have been experiencing rapid uplift. The middle Jurassic, upper Jurassic, and Cretaceous rocks at the surface have been uplifted approximately 1.8 km since the end of the Eocene. This uplift may have influenced fault movement in the Colorado Plateau and along the Little Grand Wash fault, and Salt Wash and Ten Mile Graben. In evaluating these deep aquifers for CO₂ sequestration, careful design and monitoring of the geological structure and stress regimes must be considered to avoid leakage.

Checksum

6f4575e773250ed3359c38e9260314d8

Recommended Citation

Williams, Anthony P., "Structural Analysis of CO2 Leakage Through the Salt Wash and Little Grand Wash Faults from Natural Reservoirs in the Colorado Plateau, Southeastern Utah" (2004). All Graduate Theses and Dissertations, Spring 1920 to Summer 2023. 6733.
https://digitalcommons.usu.edu/etd/6733