Petro-Hunt Nomenclature

One of the parlor games for those of us with too much time on our hands is try to decode the names of the wells.

The folks on the Bakken Shale Discussion Group tried explaining EOG's "100" vs "101" nomenclature, suggesting that the 100/101 series was the way EOG was designating wells that were targeting the Bakken formation or the Three Forks formation. That discussion never seemed to fully explain EOG's numbering system; if it did, I missed it.

Now, for those with too much time on your hands, look at the names of the Petro-Hunt wells inside the Fort Berthold Indian Reservation:

Fort Berthold 147-94-1A-12-1H
Fort Berthold 147-94-2A-11-1H
Fort Berthold 147-94-3A-10-1H
Fort Berthold 148-94-9D-04-1H
Fort Berthold 148-94-17D-08-1H
Fort Berthold 148-94-19B-18-1H
Fort Berthold 148-94-22A-27-1H
Fort Berthold 148-94-25A-36-1H
Fort Berthold 148-94-35D-26-1H
Fort Berthold 152-93-17C-08-1H 
Fort Berthold 152-93-18B-19-1H
Fort Berthold 152-94-14C-11-1H
Fort Berthold 152-94-22D-15-1H

The first two numbers are easy: that is the township (T152N-93W, T148N-94W, for example).

The next two numbers are also easy. For example, take 17C-08.  This means the well is sited in section 17 and the lateral will be a long lateral, drilling through section 17 into section 8.  Again, take the second well above, 1A-12, means that the lateral will start in section 1 and drill into section 12. (Note, occasionally, the well could be sited just inside an adjoining section but will target the sections noted in the name of the well.)

Finally, the last alphanumeric, general "1H." The NDIC requires that wells in each section be chronologically numbered, and thus the "1": the first well in this section. The "H" obviously stands for "horizontal" well.

But we've left out one letter in the name of the well. The letter that I do not understand is the letter that follows the third number, the number that designates the section in which the horizontal lateral begins. In the first well noted above (Fort Berthold 152-93-17C-08-1H), the letter I am referring to is the "C." The letters used are A, B, C, and D. I have no idea to what the letters refer. It does not appear to refer to the quadrant in which the well is sited.

I suppose they could be referring to the formation the laterals are targeting but that would be four formations, and right now there are three formations that being targeted: the Middle Bakken, the Upper TFS, and the Lower TFS. So, what would be the fourth formation? The Birdbear? The Lodgepole?

The Petro-Hunt nomenclature is consistent through North Dakota: township designation, section-section, alphanumeric numbering. And the enigmatic letter following the first section.