Assessing the Carbon Sequestration Potential within the Bear River Formation of the Wyoming-Idaho-Utah Thrust Belt
Ronald M. Drake II and Matthew D. Merrill
The United States Geological Survey (USGS) was directed by the 2007 Energy Independence and Security Act to assess the potential geologic storage resources for carbon dioxide (CO2) within the United States. Utilizing its probabilistic methodology for a national CO2 geological sequestration assessment, the USGS has assessed the storage potential of the shale and sandstone dominated Cretaceous Bear River Formation within the Wyoming-Idaho-Utah (W-I-U) thrust belt. The basic assessment unit used in the USGS methodology is the Storage Assessment Unit (SAU), which consists of a storage formation and an overlying regional seal formation. The SAUs are defined by geologic criteria that include rock properties, formation depth, and regional extents of the storage and seal formations. The methodology requires that the storage formation be at depths from 3,000-13,000 ft below ground surface. This minimum depth requirement ensures that CO2 will remain in a supercritical phase. Within the W-I-U thrust belt, a significant portion of the Cretaceous Bear River Formation fits within this depth interval. However, in several instances, thrusted Bear River Formation overlies a repeated deeper section of Bear River Formation and rock properties indicate that CO2 could be stored at depths greater than 13,000 ft, in a separate 'deep' SAU. These thrusted and stacked SAUs yield increased potential storage. The storage formation and overlying seal are required to be continuous and regional in extent. Within the W-I-U thrust belt, there are thick, regionally extensive, marine shales (Aspen and Mowry Shales) which could inhibit the flow of buoyant CO2 into overlying strata. In some cases, the stratigraphy includes the stacked seals of the Aspen and Mowry Shales. During this assessment, the seal was evaluated for leakage potential and a minimum seal thickness of about 75 ft was defined to ensure integrity. This minimum seal thickness extends over the entire Bear River Formation SAU. These criteria were used to delineate boundaries for the Bear River Formation regular and deep SAUs within the W-I-U thrust belt. The assessed storage formation is porous and permeable and has the required overlying regional seal that meets the requirements of the assessment methodology. This USGS carbon sequestration assessment has shown that there is potential for CO2 sequestration within the structurally complex Cretaceous Bear River Formation of the W-I-U thrust belt.
AAPG Search and Discovery Article #90169©2013 AAPG Rocky Mountain Section 62nd Annual Meeting, Salt Lake City, Utah, September 22-24, 2013