Let me get this straight; you are investing in North Dakota Oil E&P companies, and you do not know what the Three Forks petroleum geological formation is? I'd suggest you google 'three forks oil", and read everything that pops up on the first 5 pages as well as the cut views of the earth's strata in this area. Then, and only then, will you understand the meaning and objectives of an oiler employing a single 4-well pad targeting the Bakken and Three Forks formations.
It is my understanding that it is a different part of the geological formation. Much of the drilling is in a part called the "middle Bakken." The Three Forks is, I believe, a deeper part of the of the formation, below the middle Bakken. I think CLR has a really good powerpoint presentation on this.