Michigan UWI (API) Numbers

Michigan’s use of the 14-digit UWI/API Number is somewhat unique, particularly in the 11^th through 14^th digits.  Be sure and read the explanation below to get a better understanding of how these digits are assigned.

Michigan uses a 14-digit Unique Well Identifier (UWI) / API number as follows:

1. The first two digits represent the state code. ‘21’ is the state code for Michigan.
    
2. The next three digits represent the county code which is determined by the county where the well’s surface location is located. County codes in Michigan start with ‘001’ for Alcona County, increasing by two for each county until the last county, Wexford County ‘165’ - is reached.
    
3. The next five digits are a unique well identifier for that particular county. In the past, Michigan populated this part of the UWI/API number (6^th through 10^th digits) with the well’s five-digit permit number. Until 1998, Michigan did not use UWI/API numbers and the five- digit permit number was a well’s only identification. To be consistent with other states, the 6^th through 10^th digit part of the UWI/API number is no longer tied to the five-digit permit number. To highlight the change from the previously used UWI/API numbering scheme, they have jumped forward to ‘62000’ in this part of the UWI/API number, and will add to that number (i.e. ‘62001’, ‘62002, ‘62003’ and so on) based upon the next well permitted in that particular county. This change will only impact permits issued after 3/6/2017, so any previously issued UWI/API numbers will remain the same. As a result of this change, there will be duplication in the 6^th – 10^th digit part of UWI/API number for different wells, but the entire UWI/API number will remain unique for a given well because of the county code. 
    
4. The next two digits are used to represent kicks or re-drills from the initial well bore. Some examples include: horizontal re-drills, directional re-drills, deepening's, and re-entries of plugged wells. For the initial well, the UWI/API number is designated by a ‘00’ in the 11^th and 12^th digits of the UWI/API number and any subsequent re-drills  are designated by ‘01’, ‘02’, ‘03’, and so on. It should be pointed out that there are also special cases - unique to Michigan - where the 11^th and 12^th digits are ‘70’ for mineral wells, ‘80’ for some brine disposal wells, and ‘90’ for wells drilled before permits were issued (pre-1927).
    
5. The last two digits are used in Michigan to document lost holes and designated with a ‘90’ in the 13^th and 14^th digits of the UWI/API number. Michigan also uses the 13^th and 14^th digits when a blanket mineral well permit is issued for more than a single test hole.  The individual holes for the blanket permit are designated by ‘01’, ‘02’ and so forth in the 13^th and 14^th digits.