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I absolutely agree with you orphan wells pose a huge problem when it comes to methane leaks and water pollution. That said CO2 injection wells operate under an entirely different suite of regulatory requirements and involve vastly different stakeholders in the initial project planning phase. I am based in the United States so I can’t speak to the regulations other countries are developing. The US is behind on adequate regulations (Congress as usual dragging their feet) but right now CO2 injection wells follow the “Class VI” requirements set out by the EPA. Injection of CO2 must be below the groundwater table, below a proven confining rock layer (to prevent any CO2 from migrating anywhere near the surface) and be at least 800 meters below the surface to ensure CO2 is under enough pressure to remain stagnant. Before, during, and after injection these wells must have a suite of monitoring tests including 4D seismic, soil gas measurements, and in-situ pressure gauges. When the well is no longer active it is plugged and the operator is still liable for the project area for 50 years. By 50 years anything that could go wrong would have done so already, most geophysical models of CO2 leaks assure its storage for at least 100 years but I prefer 10,000 years to emphasize the storage assurance.

Additionally a smart carbon capture project would utilize CO2 mineralization processes that capture the CO2 in the crystal of a mineral (like calcite). This removes the problem supercritical CO2 may pose. This process is geology dependent and works well in basaltic rocks, the Climeworks mammoth plant in Iceland is an example of this.