SOUTHERN ARIZONA CO2 STORAGE: A PRE-FEASIBILITY STUDY IN HARQUAHALA BASIN

The Arizona Geological Survey within the University of Arizona is actively investigating geologic sites across Arizona where carbon dioxide (CO₂) can be permanently sequestered in the deep subsurface. Harquahala basin is one of 57 sedimentary basins in southwestern Arizona with the potential to store large volumes of CO₂ at depth. A Phase-I pre-feasibility study was conducted with funding from the U.S. Department of Energy (DOE) through the Carbon Utilization and Storage Partnership West Regional Initiative.

The Phase-I study integrated all available datasets which included a surficial geologic map compilation, well information (lithology, temperature, salinity, and proxy data), gravity, aeromagnetics, and five newly re-processed 2D vintage seismic lines. Our findings show that Harquahala basin meets initial criteria necessary for geologic carbon storage: 1) sufficient pore space volume below ~800 m (~2,600 ft) depth in porous and permeable clastic basin-fill deposits (CO₂ reservoir with the potential to store an estimated 1,997 Mmt of CO₂ (P50)); 2) storage within saline groundwater (>10,000 ppm TDS); 3) storage below an impermeable seal (bedded evaporites and clay) that separate the CO₂ reservoir from USDW aquifers; and 4) proximity to CO₂ emission sources and pipeline infrastructure. Additionally, mafic lava flows likely present within the reservoir rock serve as a strong candidate for rapid CO₂-mineralization. Geothermal potential and historic seismicity were also evaluated and integrated into the study. Our analyses yielded new information about the basin size, geometry, and structure, which improved calculations of the area and volume of the potential carbon storage reservoir. To help engage and educate communities, landowners, and stakeholders, we built an online Story Map summarizing the Harquahala CCUS concept.

To validate Phase-I findings and address data gaps, a Phase-II feasibility study to collect new high-resolution geophysical data and drill a deep stratigraphic test well was proposed to DOE’s CarbonSAFE II initiative in March 2024 (pending). Proposal development yielded strong utility, stakeholder, and industry support. Our efforts to advance CCUS in Harquahala coincides with efforts by the state to develop UIC Primacy (in EPA review) and revised statutes addressing pore-space ownership, risk, and liability related to CCUS in Arizona.