Exotic Carbonate Mineralization Recovered from a Deep Basalt Carbon Storage Demonstration

Area of Science:

• Geochemistry
• Geology
• Environmental Science

Background:

• Climate change mitigation necessitates advanced carbon dioxide removal (CDR) strategies.
• Geologic carbon sequestration in reactive subsurface environments is a key CDR approach.
• The Wallula Basalt Carbon Storage Pilot Project investigates CO2 mineralization in basalt.

Purpose of the Study:

• To analyze mineralogical and chemical changes in basalt cores two years after CO2 injection.
• To characterize the products and paragenesis of subsurface carbon mineralization.
• To provide insights into the long-term fate and transport of sequestered CO2.

Main Methods:

• Optical petrography of sidewall cores.
• Micro-computed X-ray tomography (micro-CT).
• Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS).
• Downhole fluid sampling and analysis.

Main Results:

• Discovery of chemically zoned carbonate nodules (ankerite-siderite) with Ca/Mn-rich cores and Fe-dominant rims.
• Clarification of the paragenesis and timing of secondary minerals like aragonite, silica, and zeolites.
• Confirmation of CO2 mineralization occurring on month-year timescales in basalt reservoirs.

Conclusions:

• The study provides unique insights into carbon mineralization products from a real-world geologic carbon storage field site.
• Understanding these mineralization processes is crucial for assessing the permanence and effectiveness of CO2 sequestration.
• Results inform the future design and monitoring of carbon storage projects in mafic-ultramafic rock formations.