Sealing the past: The plugging of Alaska’s Legacy Wells

The Bureau of Land Management’s Legacy Wells Program is a complex and ongoing project that involves the monitoring, prioritization and plugging of existing wells located in the National Petroleum Reserve in Alaska (NPR-A). Unlike other well plugging efforts in the lower 48, working within the NPR-A calls for unique scientific innovation and adaptation.

Formerly known as Naval Petroleum Reserve No. 4, the NPR-A is a roughly 23-million-acre roadless area located 200 miles north of the Arctic Circle. Its role in the overall story of oil resources in Alaska dates back to the early 1900s when field geologists from the United States Geological Survey (USGS) explored the North Slope of the Brooks Range in Alaska to evaluate its mineral potential. When the team discovered several oil seeps in the area, President Warren G. Harding established the Naval Petroleum Reserve No. 4 (NPR4) in 1923.  

Following its establishment, the U.S. Navy and the USGS drilled a total of 136 test holes in the NPR-A.  Husky Oil Corporation was contract for this effort with the purpose to locate oil and gas resources while developing new technologies and pad design for drilling in the Arctic; these holes are what we now refer to as legacy wells. In 1976 the BLM was given responsibility for managing the NPR-A and in 1982 upon the dissolution of the USGS Conservation Division, BLM was delegated to oversee all onshore oil and gas actions on public lands. Since 2002, the BLM has been working to systematically plug and clean up legacy wells throughout the NPR-A.

Left unattended and unplugged, inactive oil and gas wells are environmental hazards that jeopardize public health and safety, as well as pose risks to wildlife. Emissions of noxious gases like methane threaten to contaminate groundwater; unattended drill sites can lead to flooding and sinkholes.

Oil and gas well plugging is a multi-step process. Before the actual plugging can begin, specialists must inspect and prepare the site and determine if there are any existing infrastructure and production tubing in need of removal. Strong plugging materials with low permeability, such as cement, are then pumped into well systematically. Underground plugs across the oil and gas production zones and water aquifers seal off the porous rock formations.

Assuming the plugs pass   pressure tests, and no adjustments are needed, the well is then capped, and reclamation activities begin when necessary. The Bureau of Land Management establishes minimum plugging and abandonment requirements for onshore oil and gas wells on Federal lands and reclamation aims to restore the site to match its surrounding environment. The BLM’s strategy is to closely monitor Legacy Wells in the NPR-A, first plugging and remediating wells that pose a potential risk. The agency’s Legacy Wells Strategic Plan is regularly reviewed and updated with current data and goals to guide the BLM’s prioritization of future plugging and remediation efforts.

The Legacy Wells Program offers both unique challenges and opportunities to the BLM. In ideal conditions, plugging and restoring the surface area of a single oil well can take a year or longer. However, the vast, remote location of the NPR-A and timing restrictions characteristic of working in the Arctic make for a lengthy, expensive process.

Unlike plugging operations in the Lower 48, Legacy Well plugging operations require work to occur in very different conditions. Access to the wells can only occur in the winter due to delicate structure of the Arctic Tundra. To prevent damage to the tundra, equipment is modified to lessen the ground pressure. This may be accomplished by substituting tires for tracks. Authorization to drive across the tundra must wait until a substantial amount of snow cover is in place and a specific frost depth is achieved. These conditions are key for protecting the tundra which takes years (or decades) to recover for specific plant species found in the unique arctic ecosystem.

The logistics and planning necessary to plug the Legacy Wells take months of careful preparation, multiple permitting processes and sourcing of specialized equipment. Depending on the project complexity the preparation alone can take 6-8 months if not more. Planning is the key to the successful execution of these projects; we can’t just drive down to the nearest store and get a part or new equipment if needed. Everything needed for a project is mobilized to the remote site via snow trails. Depending on the project the trails are well over one-hundred miles long one-way taking several days to traverse.

Each Legacy Well project has its own challenges and requirements based on factors such as location, downhole conditions of the well, historical material used for drilling, and specialized equipment needs to name a few. A common factor amongst the wells has been the need to thaw out ice plugs across the permafrost layer of the well (over 1000 ft deep in some places). Occasionally wells only need a surface plug as they were plugged with cement in the deeper section of the well prior to abandonment by the Navy or USGS.

Another unique situation encountered with Legacy Wells is the threat of coastal erosion. Several wells were drilled near the coastline of the NPR-A and over time that coastline has receded. Wells in these areas are closely monitored, and if the coastline erosion threatens to reach the well sites, plans and funding are allocated to address the situation Wells in these areas are closely monitored, and if coastline erosion threatens any well sites, plans are made to address the issue, with funding secured in a reasonable and effective time frame.

The materials used to plug Legacy wells are quite similar to those found in the Lower 48, such as cast-iron bridge plugs, cement baskets and cement. Due to the frozen ground conditions a special blend of cement is utilized called ‘Arctic Blend’ so that it will properly harden in the colder conditions unlike other cement types that are used for non-nonfrozen subsurface.

Special care and consideration are put into each step of the process to ensure the BLM, and its contractors are protecting the Arctic ecosystem and accomplishing well plugging and reclamation for the long-term goal of improving and preserving the habitat. Some steps of the project provide challenges and require coordination with other agencies.  The BLM coordinates aspects of the Legacy Wells Program with other Federal Regulators, State and local regulators, including the Alaska Oil and Gas Conservation Commission (AOGCC), Native Corporations, and the Alaska Department of Environmental Conservation (ADEC), on the planning for the remediation of Alaska legacy well sites, including addressing their input on project goals, design, and standards.

Collaboration with Native-owned small businesses empower the BLM to staff projects and accomplish important work on the ground. Together, the BLM and its partners have addressed priority wells each season since 2002.

Currently, only 22of the initial 136 wells remain, 16 of which are being used by the U.S. Geological Survey to monitor temperatures in the Arctic. That leaves the BLM with 6 wells needing to be plugged. As specialists work to update the upcoming 2025 Legacy Wells Strategic Plan, risk analysis, monitoring data, and partnership opportunities will inform the agency’s next steps and move the BLM one step closer to achieving this goal.