Looking at Maps Sparked an Idea

What Makes Williston Trends End?

Too often the public perception of the petroleum industry may be that of a fiefdom ruled by the major oil companies whose executives sit in some secret room and control the energy resources of the world.

OK, we all know that's ridiculous.

But while majors command the lion's share of worldwide production, sometimes it's the little independent shops that -- through creative thinking -- can advance the science of geology and conceive new ideas about petroleum systems around the world.

Independent geologists working in small offices all over the United States still approach their science the old fashioned way: They earn it, and through years of experience they conceive new ideas about old problems, and with hands-on, detailed study of existing data develop new play concepts for explorationists to test.

That's just what one Crawford, Colo.-based independent geologist has done in the Williston Basin.

W. Richard Moore applied his 30 years of experience in the Rocky Mountain region to a puzzle that has baffled the industry for years, And he just may have a solution.

"Major producing trends in the Williston Basin terminate for no apparent reason," Moore said.

The basin's northeast part in Canada is extremely prolific with about four billion barrels of recoverable oil -- fairly well outlined production areas. But as those Mississippian and Ordovician producing trends enter North Dakota the number of fields decreases dramatically.

"The Mississippian trend that accounts for much of the oil in Canada stops rather abruptly as it enters the United States," Moore explained, "and there's never been a good explanation for why it stops."

This leaves much of the southern and eastern portions of the basin with little production.

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Too often the public perception of the petroleum industry may be that of a fiefdom ruled by the major oil companies whose executives sit in some secret room and control the energy resources of the world.

OK, we all know that's ridiculous.

But while majors command the lion's share of worldwide production, sometimes it's the little independent shops that -- through creative thinking -- can advance the science of geology and conceive new ideas about petroleum systems around the world.

Independent geologists working in small offices all over the United States still approach their science the old fashioned way: They earn it, and through years of experience they conceive new ideas about old problems, and with hands-on, detailed study of existing data develop new play concepts for explorationists to test.

That's just what one Crawford, Colo.-based independent geologist has done in the Williston Basin.

W. Richard Moore applied his 30 years of experience in the Rocky Mountain region to a puzzle that has baffled the industry for years, And he just may have a solution.

"Major producing trends in the Williston Basin terminate for no apparent reason," Moore said.

The basin's northeast part in Canada is extremely prolific with about four billion barrels of recoverable oil -- fairly well outlined production areas. But as those Mississippian and Ordovician producing trends enter North Dakota the number of fields decreases dramatically.

"The Mississippian trend that accounts for much of the oil in Canada stops rather abruptly as it enters the United States," Moore explained, "and there's never been a good explanation for why it stops."

This leaves much of the southern and eastern portions of the basin with little production.

Analyzing the Data

To better understand what controls the producing trends and, therefore, have a model that can be used to develop new trends, Moore collected and analyzed several data sets, including Bouguer gravity, geothermal gradients and surface linear patterns.

"I was working at developing prospects, and initially I was doing a study of the Niobrara formation in the Denver Basin," Moore said. "I became intrigued by what I was seeing in the geothermal gradient, so I went back and started looking at areas of high geothermal gradient and negative gravity anomalies and saw there was a correlation between the two.

"I love looking at all different kinds of maps, and I saw a hint," he continued. "This is one of those happenstances where you suddenly see a correlation and set out to understand it."

All of these data are readily available, Moore said. Both Bouguer gravity and surface linear information are accessible in published literature and he made geothermal gradient maps based on temperature readings in area well log data.

"You don't need a lot of high quality seismic data to get a basic outline for some new play areas," he said. "You can assimilate this type of existing information and get a good first look at a region."

Analysis of the data sets in the Williston Basin showed a strong correlation between areas of hydrocarbon production, high geothermal gradient, high intensity of surface linears and negative Bouguer gravity anomalies.

Based on his study Moore believes that these areas of strong correlation reflect high fracture intensity in the basement and overlying sedimentary sequences and that these fracture systems control trap formation and hydrocarbon migration.

"As you come south of the known trends, hydrocarbon production stops because the basement fracture systems terminate," he said. "You can see on the data sets that lower geothermal gradient, positive Bouguer gravity and a lower intensity of surface linears characterize these non-productive regions."

While there are no definite answers to why the fracture systems terminate, Moore said it's likely related to basement lithology or basement tectonics down in the Earth's mantle or crust.

"If you look at the surface of the earth, there are areas that are highly fractured and areas that aren't, and we really don't fully understand why you have fractures in one area and not in others," he said. "But basement lithology and tectonics are the likely determining factors."

Signs of Potential

Based on his study, Moore believes he has identified some potentially prospective areas in the Williston Basin and other Rocky Mountain basins as well.

"I found in the southeastern portion of the basin these areas of high geothermal gradient, Bouguer gravity minimums, and high surface linears are duplicated," he said. "I think a large area of over 3,000 square miles in the southern Williston Basin can be shown to be highly prospective in several Paleozoic horizons."

Significant production offsets the potential area, and hydrocarbon shows exist in the few wells that have been drilled in the area, he added.

This prospective area is east of the producing regions of the Williston and west of Bismarck in Morton and Grant counties of North Dakota. Along the edge of this area of concentration of geothermal gradient, surface linears and Bouguer gravity minimums there are three significant fields that produce from the Ordovician Red River or the Cambro-Ordovician Winnipeg formations.

"In my mind this is another area with significant basement fracturing that should have traps primarily in the Ordovician and the Winnipeg," he said.

Buffalo Creek, a one-well field that produces from the Red River, has pumped about 600,000 barrels of oil since the mid-1970s. The Taylor and Richardton fields were discovered in the late 1970s to early 1980s, and both produce from the Winnipeg.

  • The Taylor Field has produced about six billion cubic feet of natural gas with ultimate recoverable reserves of around 10 billion cubic feet from one well.
  • The Richardton Field has made about three billion cubic feet of gas.

There also have been some significant shows in this prospective area from the same zones that produce at Buffalo Creek, Taylor and Richardton.

"These shows are important -- they are a strong indicator that the region has potential," Moore said. "There have only been 10 wells drilled in this 3,000-square-mile area, and five of those wells had significant shows of gas from the Winnipeg."

Risky Business

Natural gas was not an exploration focus for the majority of operators when these wells were drilled, and the producing formations are found at 10,000 feet, making the wells relatively expensive to drill.

Of course, that's all changed. Today a growing list of companies are actively searching for new natural gas plays, and substantially higher natural gas prices are expanding the economic limits of exploration opportunities.

"This combination of factors could certainly heighten interest in this area and (perhaps) prompt some companies to test the region," Moore said. "It's a matter of someone willing to jump in and take the risk."

Individual wells have the potential to make a minimum of 10 billion cubic feet of gas or upwards of one million barrels of oil, Moore believes.

"Plus, this is a complex play that will require multi-well programs to tap the subtle structures in the regions," he added. "This is a huge area that's virtually untapped, but could potentially yield trillions of cubic feet of natural gas."

Moore is conducting this same type of study on other Rocky Mountain basins.

"We see large non-productive areas right next to highly productive regions all over the Rocky Mountains," he said. "The conventional explanation has always been a lack of exploration. However, today I think more people are recognizing that we must look at basement tectonics and its control on producing trends."

Identifying these potentially productive regions based on geothermal gradient, Bouguer gravity and surface linears is an ongoing project for Moore.

"I think the same type of basement tectonics I saw in the Williston Basin controls almost all of the hydrocarbon systems in the Rockies," he said, "and by mapping these areas of high fractures we can better understand old producing trends and explore for new trends.

"This is not confined to the Rockies either," he added. "Many of the eastern U.S. basins share these same characteristics, including the Michigan Basin, the Illinois Basin and the Appalachian Basin."