The Bakken formation, mostly in North Dakota, is turning out to be one of the most prolific oil plays in the history of the United States. It was named after Henry Bakken of Tioga, N.D., in 1953. It was his farm on which the discovery well was drilled. It didn't produce too much oil per day but, remarkably, the well is still in production! In 2007, the United States Geological Survey (USGS) estimated that there might be as much as 3.65 billion barrels of oil in the Bakken. In 2012, estimates revised that up that to a mean of 18 billion barrels, with recoverable oil around 7.4 billion barrels. That is, recoverable with today’s technology. Drillers are an inventive bunch and, if history is any guide, much more oil will be recoverable.
Part of the problem with the Bakken, in the early days, was the formation itself. These shale plays are called “unconventional” because they are source rock and reservoir, all in one. Conventional oil wells tap reservoirs almost exclusively, the source rock being deeper and harder to get at. The Bakken is also not very thick. It ranges from 30 or 40 feet thick in some areas to 300-plus feet thick in others. Since most drilling “back in the day” was vertical, it didn't open much formation to the well-bore. The other problem was permeability (measured in milidarcys). The porosity is fair, thus trapping a fair amount of oil, but with low permeability, the oil would not flow to the well-bore.