Class VI Underground Injection Wells

(See endnotes 65, 67)

Class VI underground injection wells are used to inject carbon dioxide into areas where oil and gas have been removed, deep aquifers containing saline, and other deep formations for the storage and disposal of carbon dioxide to mitigate its effects on global warming. There are numerous concerns that need to be answered before Class VI injection wells can actually be put into operation in a meaningful way. These technical and regulatory issues include but are not limited to: who owns the injection zones; the cost of injection; the problem of carbon dioxide migrating underground; the long-term effects that carbon dioxide may have on the area in which it has been injected; etc.

Best Practices for Class VI Underground Injection Wells

  • • Apply for a permit from the authorizing authority to establish a Class VI injection well or modify an existing injection well to become a Class VI. Include a map with cross-sections, list location and description of all injection wells whether producing or closed within the review area, and information on geological structure, hydrogeological properties of the site, suspected faults and fractures, seismic activity and history, depth of well, confining zone, and injection zone, and other data required by the authorizing authority. Include information on the average and maximum injection pressure, sources, and analysis of the chemical and physical characteristics of the carbon dioxide stream.
  • • Install the injection well on a site that has an injection zone of adequate (areal) space or surface with a proper amount of thickness, porosity, and permeability to accept the entire volume of carbon dioxide over the course of the life of the well. The confining zone must be free of any faults or fractures or permeability that would allow the carbon dioxide to move through it to another area. There will be an area of review and corrective action around the well in which testing will be necessary to make sure that no problems are created by the injection well and its contents.
  • • All Class VI wells must be constructed to: prevent the movement of fluids into or between drinking water strata; have structural strength for the cement and other materials which is compatible with the material being used in construction; be compatible with the carbon dioxide and any other associated fluids; and last the life of the geological sequestration.
  • • Provide to the authorizing authority the following information: depth to the injection zone as well as injection pressure, external pressure, and internal pressure; hole size and size and grade of all casing and cement as well as the extent of the casing above the ground and under the drinking water strata; corrosiveness of the carbon dioxide and associated fluids; quantity, chemical composition, and temperature of the carbon dioxide stream as well as the down hole temperatures; the tubing, its size and composition, packer materials and their compatibility with the carbon dioxide stream and other fluids.
  • • Analyze the carbon dioxide stream frequently to determine chemical composition and physical characteristics.
  • • Monitor continuously potential corrosion of injection well materials, injection pressure, rate, volume, and the annulus pressure.
  • • Monitor groundwater quality and any geochemical changes above the confining zone.
  • • Establish a well plugging plan and have it approved before the well is plugged.
  • • Prepare a plan for the postinjection care of the site including postinjection monitoring on a regular basis.
  • • Provide the authorizing authority with an emergency and remedial response plan in the event that the movement of the injected fluids or associated fluids will endanger the drinking water strata. Immediately cease all injection.
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