A reader left an excellent comment that I couldn't have written better myself and which deserves better prominence:
I am not a reservoir engineer but can offer some comments based on observing Williston Basin production over the last 50 years.
Initial production is always a good indication of performance, but there are great variances. One well which IP'd for 162 barrels per day has produced 1,463,000 barrels so far; it's still producing. Another with an IP of 480 barrels per day has produced 2,356,000 barrels to date and continues to produce. I believe this is the granddaddy of all North Dakota oil wells...so far. (Both of these are vertical Madison wells producing from relatively thin pay zones, 164-85.) Another extreme is a Nesson Anticline well with an IP over 1,000 barrels per day that was plugged after only a few months (vertical Interlake).
More to the point, I believe you need 18 to 24 months of production to get a good feel for what a well is going to ultimately produce. Since only a few horizontal Middle Bakken and Three Forks wells have more than a year of productive history, it is difficult for me to draw any firm conclusions. It appears that if you average the first 2 to 3 months of "flush production", the typical well might be producing 50% of this average amount in 10 months to a year. After 15 to 18 months in appears production has leveled off at a rate of about 25-30% of the first 3 month average (with little regard to the IP rate). Hopefully the decline from this point forward will hold at about 10%-15% per year.
The obvious exception to the scenario is the Petro-Hunt USA 2D in the Charlson area. It's reported IP was 700 barrels per day. It's 16 month total production is 378,536 barrels and the most recent month production was 1000 barrels per day! This was its best month ever; it is "inclining" not declining(?).
Other cautions on every well: did they stay "in zone" while drilling; did the zone get damaged while drilling; did the direction of the lateral section optimize natural fracturing, did the frac job get into the intended zones, and on and on. We'll all be wiser in a few years as this data base grows and learning curve goes higher.
Anyway, regardless of Williston Basin history, the future looks extremely bright! The Bakken play has been nothing but fantastic. Also, we have to remember, this is a play brought on by technology: horizontal drilling and fracing. Both of these will only get better and we've just scratched the surface of the Middle-Bakken potential. Who knows where the Three Forks will take us.
Continental is planning some upper Three Forks wells in the near term so by the end of the year we should have a little better idea of the potential of that zone.