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Wold Drilling

The Nabors X21 rig operates at a Wold Energy Partners well site in March 2018 north of Rolling Hills in Converse County. A new study suggests geology matters more than engineering in predicting a well's success. 

At some point in recent years, drilling in Wyoming and in many parts of the U.S. became an engineer’s game.

The long horizontals wells and the ever bigger hydraulic fracs drew the attention of the oil and gas industry and investment dollars from Wall Street. The crucial denizens of this industry — geologists — came to share prominence with engineers when it came to finding and drawing out hydrocarbons from sandstone and shale.

But a popular drilling target beneath the soil of the Powder River Basin appears to operate by older rules. For the Turner play, it’s about the rock.

At least it appears to be in a recent study from the Wyoming State Geological Survey about the horizontal wells of the Turner, one of the most popular layers of rock being targeted by drillers in Wyoming’s Powder River Basin.

“It appears that the location of a horizontal well in the Wall Creek-Turner, especially in regards to the reservoir depth and temperature, is a better predictor of production success than well design,” oil and gas geologist Rachel Toner, the study’s author, said in a statement.

What Toner did was compile two data sets. In one, she considered the geological components surrounding completed horizontal wells in the Turner and Wall Creek, like heat and pressure. In another, she considered what the drillers had done, like the number of fracks, amount of proppant and the direction of the well.

Then she compared the data. Was it geological factors or drilling strategy that drove the better producing wells? The numbers say geology.

The Turner

The Powder River Basin didn’t exist 90 million years ago. What did exist was an inland sea. The Turner and Wall Creek were part of a sandy delta.

Picture Louisiana, where triangles of sediment intersperse with wetlands deposited by the Mississippi River as it flows into the ocean.

Such sandy stretches — overlaid with more dirt, sand and organic material — pressed down, heated and cooked into rock over millennia. That’s the Turner and Wall Creek, two sandstone layers that vary in thickness and depth beneath Powder River Basin. Some argue that they are actually one in the same. In any case, they are equivalent in time, Toner said.

Recent horizontal wells have attracted more and more attention in the last few years. Large independents like EOG Resources and Anadarko, and private companies like Wold Energy or Anschutz, have targeted the Turner in drilling plans.

The first long horizontal in the Wall Creek-Turner was drilled by Chesapeake Energy and came online in 1994, according to the report. The report focuses on production in the last 10 years.

Many feel like they’ve unlocked some layers in the Powder. A tipping point has been reached in the growing body of knowledge for how to approach drilling these areas. It’s in part spurred a record interest in development there.

But the Powder, particularly some of its less explored rocky layers, is still new. There’s a lot that isn’t known yet, Toner said.

“They are doing a really good job pulling oil out of it,” Toner said of the Turner.

The geologist noted that current horizontal development in the Turner and Wall Creek still hasn’t tapped the most overpressured regions. The Turner is getting more attention from drillers, compared to its sister rock, Wall Creek; it is cooler and less pressured.

The Turner is of particular interest in the Powder River Basin. From 2017 to 2018 the Wall Creek and Turner wells were responsible for 33 percent of the oil and 23 percent of the natural gas produced in the basin. From 2017 to the time of the report, 17 percent of approved permits to drill in the Powder targeted the Turner and Wall Creek.

As noted by the Wyoming State Geologist Erin Campbell in a release accompanying the study, the Turner is often the subject in hearings that come before the Wyoming oil and Gas Conservation Commission.

“It is important for the survey, and the state as a whole, to understand the drivers of production from the Wall Creek-Turner reservoir,” Campbell stated. “Many protested applications heard before the Wyoming Oil and Gas Conservation Commission involve these formations. This report can help the commission make decisions that best benefit Wyoming in terms of efficient and highly productive drilling.”

The Powder

Competition over drilling rights and land position in the Powder has led to a record number of applications for permits to drill filed with the state, hitting 25,000 by the end of 2018. Part of that rush is due to success with individual wells. What the basin’s cheerleaders say they have accomplished in the last few years is akin to finding the right pieces in a puzzle.

Ron Auflick, who leads operations for Wold Energy Partners and completed a spate of drilling last year, said he feels like the basin is being unlocked, that the way drilling is being investigated and tested is changing the game for the Powder.

The company is one of the top five for permit applications filed in the Powder River Basin.

The WSGS study is excellent for operators, he said.

“All rock is not created the same, like that,” Auflick said. But he also noted that the drilling approach is still vital, still in play.

“I personally believe that each formation has a code to crack in terms of (drilling) and it’s early days for us,” he said of Wyoming’s Powder River Basin.

It is still early in the Powder’s development, Toner said.

She did what she could with the data available, and it revealed a dynamic story. But industry is still out there drilling and they are likely going to be drilling longer wells, she added.

The Turner may or may not be as old school as it appears at this point in time.

“It could end up being an engineer’s game,” Toner said. “But, maybe with an eye on the geology.”

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Energy Reporter

Heather Richards writes about energy and the environment. A native of the Blue Ridge Mountains in Virginia, she moved to Wyoming in 2015 to cover natural resources and government in Buffalo. Heather joined the Star Tribune later that year.

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