Workers with Raven Drilling line up pipe while drilling for oil in the Bakken shale formation outside Watford City, North Dakota.

In a corner of the prolific Bakken shale play in North Dakota, oil companies can now pump crude at a price almost as low as that enjoyed by OPEC giants Iran and Iraq.

Until a few years ago it was unprofitable to produce oil from shale in the United States. The steep slide in costs could encourage more U.S. shale output if OPEC members cut supplies, undermining the producer group's ability to boost prices. OPEC ministers meet Wednesday to weigh output cuts to end a two-year glut that has pressured global oil prices.

In shale fields from Texas to North Dakota, production costs have roughly halved since 2014, when Saudi Arabia signaled an output free-for-all in an attempt to drive higher-cost shale producers out of the market.

Rather than killing the U.S. shale industry, the ensuing two-year price war made shale a stronger rival, even in the current low-price environment.

In Dunn County, North Dakota, there are around 2,000 square miles where the cost to produce Bakken shale is $15 a barrel and falling, according to Lynn Helms, head of the state's Department of Mineral Resources.

"The success in Dunn County has been fantastic," said Ron Ness, president of the North Dakota Petroleum Council.

Dunn County's cost is about the same as Iran's, and a little higher than Iraq's. Dunn County produces about 200,000 barrels of oil a day, about a fifth of daily production in the state.

It is North Dakota's sweet spot because it boasts the lowest costs in the state, yet improved technology and drilling techniques have boosted efficiency for the whole state and the entire U.S. oil industry.

The breakeven cost per barrel, on average, to produce Bakken shale at the wellhead has fallen to $29.44 in 2016 from $59.03 in 2014, according to consultancy Rystad Energy. It added that in terms of wellhead prices, Bakken is the most competitive of major U.S. shale plays.

Wood Mackenzie said technology advances should further reduce breakeven points.

Landlocked Bakken producers still need a substantially higher international price than their breakeven cost to make a profit, since they pay more to transport crude to market than producers in most other U.S. regions.

International oil prices of $45 a barrel are enough for some Bakken producers to profit, Ness said, and $55 would encourage production growth.