Near the bottom of the Lodgepole formation along the southern flanks of the Bakken petroleum system in North Dakota and Montana lies an organic-rich limestone interval that can appear very similar to the Upper Bakken shale, to the extent the two have sometimes been confused. That confusion is what led drillers to dub the interval the “False Bakken.”
Julie LeFever, director of the North Dakota Geological Survey’s Wilson M. Laird core and sample library, describes the False Bakken as a “very, very organic rich” limestone that “looks like the Bakken when it’s wet,” except that the False Bakken is dark brown whereas the Upper Bakken shale is generally black. While the beds are highly organic-rich, LeFever says they are generally much thinner than in the shales, typically in the range of one foot.
Drillers, LeFever says, would encounter that organic rich limestone and originally think they had hit the Upper Bakken shale. “But the False Bakken fizzes when you put acid on it and it can’t be the actual Bakken shale because that doesn’t fizz.”
False Bakken organic matter
The organic matter in the False Bakken limestone is just like the organic matter in the underlying shales, LeFever says, and at a high enough content to generate oil. Even though that oil is in limestone rather than shale, she says the oil generated from the limestone would be indistinguishable from the oil generated in the shale.
LeFever says the late U.S. Geological Survey geochemist Dr. Leigh Price used to refer to the False Bakken as the “last gasp of the Bakken petroleum system” because in the origin of the organic-rich deposits, it was the last depositional environment with any restriction to get organic matter to accumulate. In other words, as one moves up through the Three Forks, Bakken and Limestone formations, the False Bakken “is the last time we see that kind of organic matter.” Everything above the False Bakken, she says, is predominantly carbonate deposits.
The Scallion member
The False Bakken is separated from the Upper Bakken shale by a thin crinoidal or pelmatozoan limestone interval known as the Scallion member. LeFever says the Scallion is not organic-rich but has always shown some staining. She says several attempts have been made over the years to tap the Scallion, and while that limestone only “gave up a little bit of oil,” the wells were not capable of sustaining production.
How widespread and how thick?
Although she says she has “kept track” of the False Bakken over the years, LeFever has never formally mapped it. But she does know that it extends beyond the Bakken petroleum system.
“Usually by the time you get out of the Bakken, you quit mapping,” she says. However, she adds it is very prominent along the southwestern margin of the Bakken petroleum system in North Dakota and into Montana.
The thickness of the False Bakken can range anywhere from approximately 20 feet to 120 feet in North Dakota, and it thins toward the center of the Williston Basin. LeFever says a reasonable average thickness might be in the range of 20 to 40 feet across the basin. “It thins to the north, so I think it’s more of a wedge around the southern rim of the basin.”
Whether or not the False Bakken is a prospective oil resource, LeFever says she has no idea and that it will have to be tested. “If I say no, I could be really wrong, and if I say yes, I could be really wrong. I think it’s just something that somebody’s going to have to drill.”
Montana prospects
There has been speculation on the Montana side of the Bakken that some operators are starting to look at the False Bakken, but Jim Halvorsen, a petroleum geologist with the Montana Board of Oil and Gas Conservation, told Petroleum News Bakken that he isn’t aware of any company that has specifically explored the False Bakken in Montana. He says he knows there has been interest in it, and he believes it could have potential, but he says there has been no confirmation of a play to his knowledge. “We don’t have any confirmation well to say that it’s an event yet.”
Halvorsen says that an operator may not specify the False Bakken as a target on a drilling application, so he may not know until after production results were available that the False Bakken was the target. However, he said he would know if anyone is drilling in that area of the False Bakken, and currently there are no active rigs there.
On the Montana side, Halvorsen says the False Bakken may not be quite as thick as it is on the North Dakota side, but adds that there is much variability in the lower part of the Lodgepole. He doesn’t know how far south the False Bakken extends in Montana, but the area where he understands there is interest is to the north and east of the Cedar Creek anticline that extends from Glendive in Dawson County south-southeast through Wibaux and Fallon counties.
But Halvorsen says there hasn’t been much activity in that area. Instead, he says, most of the recent activity in that region of Montana has been south of Elm Coulee where Slawson and Fidelity have been exploring the Upper Bakken shale, and north of Glendive where Petro-Hunt has been drilling into the Red River formation.
PetroShale’s option
In March 2012, when PetroShale struck its deal with Slawson Exploration’s Alameda Energy for an option to acquire a non-operated working interest in 37,300 acres of Mondak leases, PetroShale acquired a second option — this one to buy a 10 percent non-operated working interest in some 80,000 acres in the Montana counties of Dawson, Wibaux and Richland, the acreage collectively known by the partners as the “False Bakken leases” with Slawson in the lead as operator.
The option was for nine months and was not exercised, PetroShale executive John Fair told Petroleum News Bakken April 1, but not because there was anything wrong with the proposed project. Rather, he said it was “all about money.”
PetroShale, Fair said, is currently focused on acquisitions and development.
Privately owned Slawson, whose deals have proven lucrative for companies such as PetroShale and Northern Oil and Gas, was not yet ready to comment.
Slawson was the first company to aggressively pursue oil production from actual Bakken shale, specifically the Upper Bakken member. Almost all oil production from the Williston Basin’s Bakken petroleum system comes from the Middle Bakken member, a dolomite reservoir, where some of the oil generated in the Upper Bakken shale is thought to have migrated.
