The goal of the WESTCARB Arizona Pilot is to acquire field data on the feasibility of CO2 storage in the Colorado Plateau’s saline formations—deep-lying porous rock formations filled with saltwater that cannot economically be made suitable for drinking water or agriculture. WESTCARB’s regional characterization studies suggest that suitable CO2 storage sites lie beneath or near many of the coal-fired power plants in northeastern Arizona. The Arizona Pilot will help validate this assessment and indicate the viability of using these geologic formations for larger CO2 storage projects.

In preparation for the field test, WESTCARB researchers conducted numerous studies at the selected project site, near Holbrook, Arizona, adjacent to the ash pond for Arizona Public Service Company’s Cholla Power Plant. This effort included a review of available data from other deep wells in the area, water quality and compositional data from groundwater wells, outcrops of the target formations elsewhere in the state, and published literature on the area’s geology. Computer models were used to predict the distribution and immobilization of injected CO2 and related subsurface effects, such as the dissipation of pressure in reservoir formation fluids.

Next, the project team drilled an oil-industry type well that was used for collection and analysis of downhole fluid and rock samples, with the expectation that the well would be used for injection of 2000 tons of CO2 if downhole geologic properties were suitable. Although this is a relatively small quantity of CO2, it is sufficient to test monitoring techniques for tracking the location of the injected CO2 and ensuring compliance with environmental and health and safety requirements. During drilling, researchers kept a detailed record of the rock formations encountered. Following completion of drilling, oil-industry scientific instruments were lowered into the well to measure rock properties at various depths in the borehole. In addition, sidewall core samples were extracted.

Then the project team conducted a drill stem test to ascertain the permeability of key intervals in the geologic formations. The findings were analyzed and showed very saline formation waters and good "seals" (caprocks), as geologists predicted, but insufficient permeability in the target formation to warrant CO2 injection at this location. Accordingly, researchers have proposed drilling a second geologic characterization well at an alternate location in northeast Arizona. Given favorable permeabilities in suitably deep saline formations at other wells in the Colorado Plateau of northeastern Arizona, the area remains a prime candidate for future geologic characterizations and CO2 storage test activities. 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.