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Arizona Utilities CO2 Storage Pilot—Cholla Site

WESTCARB's geologic characterization well at Arizona Public Service Company's Cholla Power Plant, near Holbrook, acquired field data on the stratigraphy of the Colorado Plateau, where deep sandstone and carbonate strata offer promising locations for storing CO2 from the area's coal-fired power plants. WESTCARB researchers analyzed groundwater samples from these strata and confirmed that the highly-saline formation waters could not economically be made suitable for drinking water or agriculture.

In preparation for well drilling, WESTCARB researchers reviewed data from other deep wells in the area, and water quality and compositional data from shallower groundwater wells. Computer models were used to predict the distribution and immobilization of 2000 tons of CO2 injected into the bottom of the well. Although this was a relatively small quantity of CO2, it would be sufficient to test monitoring techniques for tracking the location of stored CO2.

Next, the project team drilled an oil-industry type well that was used for collection of downhole fluid and rock samples. During drilling, researchers kept a detailed record of the rock formations encountered at various depths. Following completion of drilling, electrical well logging instruments were lowered into the well to measure rock properties. In addition, sidewall core samples were extracted. The findings were analyzed and showed very saline formation waters and good "seals" (caprocks) above storage zones, as geologists predicted.

The project team then conducted a drill stem test to ascertain the permeability of the target formation. This test revealed that there was insufficient permeability to proceed with CO2 injection at this location. Despite this site-specific finding, the deep saline formations in other areas of northeastern Arizona remain prime candidates for future CO2 storage characterization assessment. The project team is grateful for the community support it received from the greater Holbrook area and Navajo County.

Major WESTCARB participants in the Arizona pilot project include Arizona Electric Power Cooperative, Arizona Public Service Company, Peabody Energy, Salt River Project, Tucson Electric Power Company, Lawrence Berkeley National Laboratory, Electric Power Research Institute, Sandia Technologies, and Errol L. Montgomery & Associates.

For detailed information and photos on the project's drilling phase, visit our Drilling Progress page. Overall project details can be found in the WESTCARB Fact Sheet. Permits issued for the field test include a Temporary Aquifer Protection permit from the Arizona Department of Environmental Quality (ADEQ), and an Underground Injection Control permit from Region 9 of the U.S. Environmental Protection Agency.