The Sanish/Three Forks Zone is an oil area below the upper part of the Bakken Shale. 

Experts and drillers are trying to figure out if the Three Forks is a seperate oil reservoir or actually part of the Bakken Shale. 

Many companies drilling in the area have shown positive results from the Three Forks.  It the case holds true, and Three Forks is a seperate oil reservoir, it could hold as much if not more than the Bakken shale.