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BLM>Alaska>Programs>Energy>Oil and Gas>NPR-A>NPR-A Legacy Wells Program >What is a Legacy Well?
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What is a Legacy Well?

The NPR-A is a 22.8 million-acre roadless area located 200 miles north of the Arctic Circle. In the early 1900s, field geologists from the United States Geological Survey (USGS) explored the North Slope of the Brooks Range in Alaska to evaluate its mineral potential. The geologists found several oil seeps that prompted President Warren G. Harding to establish the Naval Petroleum Reserve No. 4 (NPR4) in 1923, setting aside approximately 23 million acres of Alaska’s North Slope for future energy needs.  

Legacy Wells were drilled across the NPR-A prior to 1982, when BLM held its first lease sale. A total of 136 test holes were drilled under two distinct drilling periods, both sponsored by the U.S. Government to explore for oil and gas resources. In the first period, from 1944 to 1952, the U.S. Navy drilled 91 holes, locating eight small oil and gas fields (Fish Creek, Gubik, Meade, Simpson Peninsula, South Barrow, Square Lake, Umiat and Wolf Creek). In the second period, from 1975 to 1981, Husky Oil Corporation, working under contract for both the U.S. Navy and USGS, drilled 36 holes. The remaining 9 holes were drilled in the Barrow area between 1953 and 1974. These holes are categorized as an exploratory oil well, core test, or temperature monitoring well.

Exploratory Oil Wells

Umiat Legacy Well #9
Umiat #9 Exploratory Oil Well.

The Legacy Wells were exploratory wells drilled by the United States Government to gather geologic data or identify petroleum reserves present in the NPR-A.  No wells produced oil or gas. 

Core test

BLM and AOGCC inspector locating uncased core test holes Simpson #1, #2, #3, #7
BLM and AOGCC inspector locating uncased core test holes Simpson #1, #2, #3, and #7.

A core test is not an oil and gas well. It is a hole that was drilled specifically for surface geologic information.

Temperature monitoring wells

West Fisk Creek #1 temperature montioring well
West Fish Creek #1 temperature monitoring well.

The USGS is using the exploratory wells drilled during the second period of the U.S. Government's drilling program in the NPR-A to monitor the thermal state of permafrost. This data is used to determine the magnitude of contemporary climate change in arctic Alaska, and to better understand the effects of climate change on permafrost. All of these wells are properly plugged above the hydrocarbon bearing zones and into the well’s surface casing. The wells are filled with diesel fuel down to the shallowest plug at depths ranging from 744 - 2,900 feet. Diesel fuel is used since it is a non-corrosive, non-freezing liquid making it a reliable fluid for measuring temperature at varying depths. Data collection at these wells began in 1976 and will continue for the foreseeable future. If the wells need to be plugged, the diesel fuel will be extracted and the well will be properly plugged to surface.