Even booming Bakken oil production can’t stand up to North Dakota’s crippling winters.

By hindering transportation to wells and slowing the hydraulic fracturing process, severe winter weather slows production.

The No. 1 cause of the slowdown in winter months is difficulties for fracking, North Dakota Department of Mineral Resources Director Lynn Helms said. Ice and snow make it harder to get water to a site, it takes longer to heat fluids and keep them warm, and flowback water can freeze and delay the process, he said.

That’s been an issue this week.

“They are struggling at subzero temperatures,” Helms said of fracking operators. “Things get really, really slow for them.”

Shawn Wold, Tervita’s Watford City operations manager, said the Houston-based energy company will keep bumping up the temperature of frac water heaters the colder it gets outside, which takes time.

In his monthly Director’s Cut updates, Helms often cites winter weather as the reason for decreases or smaller than normal increases in daily production.

After a rough April 2011, daily production actually dropped from March numbers.

“Growth slows but then when we have a particularly severe month like we had in the spring of 2011, production can actually fall by 10,000 barrels per day or in that neighborhood,” Helms said.

With 75 percent of oil still moved by truck, a road shutdown of three or four days due to severe weather is significant, Helms said.

And on a smaller scale, a couple inches to a foot of snow on well pad access roads causes headaches for operators.

“The biggest slowdown comes from getting equipment out to those well pads,” North Dakota Petroleum Council spokeswoman Tessa Sandstrom said.

“A lot of these wells are in remote places … it just takes a little bit more time for them to clear roads to get (trucks) out to those locations.”

And in some cases, it’s not even worth it - since operators are often responsible for plowing access roads, and it takes propane and other costs to keep wells running in winter, operators sometimes just shut marginal wells down during winter months.

Wold said Tervita will shut wells if it can’t get trucks to them to unload the tanks.

Between 400 and 500 wells are expected to be shut down from about now until spring, Helms said.

“There are a lot of wells out there that produce very little oil and gas,” he said, “and it doesn’t pay to keep the roads plowed or try to get trucks in and out to keep the wells pumping.

“It’s pretty significant when you think about 400 or 500 wells being shut off for three to four months,” Helms said.

Halliburton spokeswoman Susie McMichael said in an email that the company sees a 10 to 15 percent reduction in activity during the height of winter due to operations “simply taking more time,” like for snow removal and extra travel time.

“If the actual temperature gets down to 20, 30, 40 below, nothing’s gonna run,” Wold said. “You’re just gonna have trouble.”