OCS Lease Blocks and BOEM Protraction Diagrams

The ocean is a vast place with seemingly countless resources. The Bureau of Ocean Energy Management (BOEM) has regulatory authority to manage submerged lands of the outer continental shelf (OCS) for purposes of leasing areas for energy and mineral extraction and production. In terms of wind energy development, BOEM regulates and manages this use by conveying leases within designated lease blocks. Each whole block is just under 3 miles on a side. For renewable energy purposes only, blocks can be leased down to 1/16th of a block. Oil and gas leases also use the block and protraction system, but leases are initially leased at the whole block level and then portions of the lease can later be relinquished for resale. In the Atlantic, the Pacific, and in Alaska, all boundary areas are computed in metric units. Because the Gulf of Mexico has had leases and boundaries for oil and gas existing since the 1950s, all units are English and boundaries and maps, while similar to the rest of the U.S., have a more complicated system of leasing maps, protractions, and projections. So why should you pay attention to the OCS lease blocks and BOEM protraction diagrams?

  1. Determining which blocks are of interest for your project can help communicate potential conflicts. Since BOEM leases are by whole or 1/16th of a block, a planner can start reviewing blocks that meet favorable criteria for wind or oil and gas development and from those, start to eliminate areas of potential use conflicts because of economic, military, cultural, or environmental concerns. These block areas can be listed and communicated to stakeholders and partners so that they are easily located using the protractions and blocks layers as reference. The remaining blocks can then be assessed further for their potential for project development. For example, BOEM and the U.S. Coast Guard use the block data along with Automatic Identification System (AIS) data to determine which blocks may have too much shipping traffic to be candidates for wind or other types of projects. The analysis is then combined with other block-related analyses to determine areas that may not be the best locations for energy development. What is usually made available for further study, are those whole and partial (1/16ths) blocks that were not eliminated from consideration. This is usually only the first or second analysis. Actual leasing and construction comes much later in the process.
  2. BOEM protraction diagrams help communicate locations of lease blocks. In the National Viewer, protractions are simple outlines used in mathematically delineating the OCS lease blocks, but these are also downloadable map products from BOEM that at one time were produced as paper charts. They are now available as PDFs. Blocks are related to their parent protractions.Most of the OCS protractions cover an area of 2 ° longitude by 1° latitude and contain up to 1,200 blocks. Since each protraction starts with the same block numbering system starting with block 6,000, each block should be referred to along with its parent protraction number. For instance, NJ18-02 block 7036. Protractions are computed using the International UTM Zone Numbering system, so the protraction name tells you how far from the equator the map is, what UTM zone it is in, and which of 12 maps in that zone it represents. So NJ is North (N); Lat 36-40° (J); 18 is UTM zone 18; and 02 is the 2nd of 12 possible maps. It is important to pay attention to the names of each protraction area so that you can effectively communicate which lease blocks you are interested in leasing. Protractions in most cases also have a name based on the closest large feature, similar to U.S. Geological Survey Quad Sheets. In the Gulf of Mexico, lease maps and protractions both exist, but the block numbers in lease maps also need to be listed along with the lease map name.

Quick Caveats. For more information about jurisdictional boundaries, visit Zones, Limits, and Maritime Jurisdictions.

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