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Oil Well Abandonment and Re-abandonment in California
A Guide to CalGEM Plugging Standards

When an oil or gas well reaches the end of its productive life, it must be safely abandoned to protect people, groundwater, and the environment. In California, this process is regulated by the California Geologic Energy Management Division (CalGEM), which has detailed plugging and abandonment (P&A) requirements.

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This guide, prepared by Witten Engineering, provides a clear overview of those requirements, explains why they matter, and highlights important points for operators, landowners, and city planners.

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California Hydrocarbon Zone Abandonment Requirements – Sealing the Oil and Gas Layers

Hydrocarbon zones are the rock layers that produce oil and gas. Even after production stops, they can still hold pressure or fluids. Without proper sealing, hydrocarbons may migrate upward, contaminate water, or escape to the surface.

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  • Open Hole Zones – A cement plug must be placed from at least 100 feet below the bottom of the zone to 100 feet above the top, creating a 200-foot barrier.

  • Cased Hole Zones – If casing and perforations exist, cement must cover them and extend at least 100 feet above the top perforation.

  • Special Situations – In fractured shale, multiple stacked reservoirs, or depleted zones, plugs must extend at least 25 feet below the top perforation and 100 feet above, for a minimum of 125 feet.

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California groundwater protection in well abandonment – Protecting Aquifers

Protecting California’s groundwater is a top priority. The interface where fresh water meets salty water must be sealed to prevent contamination.

  • Open Hole – Cement plug across the interface, at least 200 feet long.

  • Cased Hole (with cement behind casing) – A 100-foot cement plug inside casing is required.

  • Cased Hole (without cement behind casing) – Perform a squeeze cement job through perforations and place a 100-foot cement plug inside the casing.

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Casing Shoes – Controlling Flow Paths

At the bottom of casing strings, casing shoe plugs must be set to prevent upward flow.

  • Cement must extend 50 feet below and 50 feet above the shoe (minimum 100 feet).

  • If the shoe is dirty or unstable, CalGEM may require a deeper plug.

This step ensures that formation fluids cannot bypass the casing.

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Surface Plugs – Securing the Well Permanently

The surface plug is the final safeguard that ensures the well remains sealed at ground level.

  • A 25-foot cement plug must be placed at the surface.

  • Casing must be cut off 5–10 feet below grade.

  • A steel plate stamped with the API well number is welded to the casing stub.

This prevents leaks and provides permanent identification for regulators and landowners.

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Other Special Cases

  • Junk in Hole – If tools or pipe are stuck, cement must be squeezed through or placed above, with at least a 100-foot plug.

  • Non-Cemented Intervals – Must be filled with properly weighted mud, and annuli at the surface should be filled to prevent gas migration.

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Why California oil well abandonment compliance matters

CalGEM’s plugging standards are designed to:

  • Protect groundwater from oil, gas, or saltwater intrusion.

  • Prevent methane leaks and protect air quality.

  • Ensure land safety for redevelopment projects.

  • Maintain regulatory compliance and avoid costly penalties.

By following these standards, we ensure environmental safety in well abandonment.

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In conclusion, oil well abandonment in California is more than plugging a hole. It’s about long-term environmental protection, community safety, and regulatory compliance. By following CalGEM’s 2025 plugging requirements, Witten Engineering delivers trusted California oil well abandonment services as CalGEM-compliant well plugging experts, ensuring wells are sealed properly, groundwater is safeguarded, and land can be safely redeveloped.

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