As I have written a number of times, reserves numbers for oil are not based on the total oil though to be under the ground, but the total oil thought to be under the ground that is economically recoverable at expected prices. Changes in technology and/or oil price expectations change the amount of reserves, even without the discovery of a single new field.
Oil companies have known about the formation, and the oil trapped in it, since at least the 1950s. But they couldn't get more than a trickle of oil from the dense, nonporous rock.
That began to change in the early 2000s, when companies in Texas began using new drilling techniques in a similar formation near Fort Worth known as the Barnett Shale. They would drill down thousands of feet and then turn and go horizontally through the gas-bearing rock"”allowing a single well to reach more gas. Then they would blast huge volumes of water down the well to crack open the rocks and free the gas trapped inside.
The real shift has come in the past two years as companies honed drilling techniques, leading to bigger wells, faster drilling and lower costs. Marathon, for example, last year took an average of 24 days to drill a well, down from 56 days in 2006."
So apparently, oil production in North Dakota may soon pass that of Alaska, though this is more due to the fact that production can be ramped up in North Dakota without an act of Congress, which is not the case in Alaska.
The largest threat to oil prices and production remains not peak oil, but the fact that most of the world's best reserves rest in the hands of state-run oil companies whose competence and willingness to invest for the long-term is sometimes in question.