The North Dakota Geological Survey’s Wilson M. Laird Core and Sample Library currently houses more than 400,000 feet of core and some 38,000 boxes of cuttings samples, allowing geologist Julie LeFever, who has managed the library since 1987, to gain a lot of insight into the geology of the Williston Basin.
In a recent interview with Petroleum News Bakken, LeFever said she believes the information maintained in the library significantly contributed to the rapid rate at which exploration has proceeded in the current Bakken petroleum system play.
The collection, she said, “is primarily the reason the Bakken play took off like it did in the state.
“The rocks were there, we had a good collection. It didn’t answer all of the questions,” she said, “but it answered a lot of them.”
LeFever also noted that coring activity in the current Bakken play is far different from the activity in earlier Williston Basin plays when only the early wells were cored. Now with the unconventional play, she said, companies continue to core and those cores are getting longer as exploration of the petroleum system continues.
“This is very, very different than the earlier plays that I experienced in the late 1980s, early 1990s,” she said. “It’s been pretty amazing to watch.”
LeFever said in some months she won’t see any new cores, but this month, which she described as a “banner month,” the library will receive five cores. Cuttings, on the other hand, come in daily.
Pronghorn member recently defined
The recently defined Pronghorn member of the Bakken system is an example of how valuable core can be. The Pronghorn is a dolomite member that lies below the Lower Bakken Shale, but until three years ago, nobody even knew the Pronghorn existed, LeFever told Petroleum News Bakken. (See Continental chart page 3.)
People had only seen “bits and pieces” of the formation in individual cores, but the library received one long, single core, she said, that cut the entire section and identified the formation. That core, LeFever added, explained those “bits and pieces” that people had been seeing in other cores.
The Pronghorn, which can be up to 60 feet thick, is very similar to the Middle Bakken dolomite member, where most Bakken oil production comes from.
The Pronghorn, she said, is “turning out to be quite the oil play.”
There is some E&P company interest in the Lodgepole, LeFever said, but where that will go “is anybody’s guess.”
Interest in Three Forks lower benches and Birdbear
LeFever said she has heard that some companies are looking at the lower two of the four benches that comprise the Three Forks formation.
“The first two benches have been proven to be productive. We do have cores that show saturations in the lower two benches (EOG Resource wells). We also have cores that do not show saturations in the lower two benches. It is possible that they may produce in (some) areas; the big question is whether they will be economic,” she said.
She said companies are also looking deeper into the Birdbear formation, which lies just below the Three Forks and is also oil bearing.
Birdbear is predominantly limestone capped by anhydrite, LeFever said.
Longer cores
Until recently, LeFever said, companies typically cored from the Lodgepole formation through the Bakken where cores ranged about 120 feet in length. But now with the Three Forks producing, and possible production below the Three Forks, companies are coring all the way down to the Birdbear formation.
Some of the cores now are in the range of 300 to 350 feet long, with one approaching 400 feet.
“That,” she said, “is a long core.”
False Bakken, another gets attention
Another member in the Bakken petroleum system that has garnered some interest from E&P companies, LeFever said, is the False Bakken, a shaley limestone toward the base of the Lodgepole. One company has even looked at a limestone section that sits between the False Bakken and the Upper Bakken Shale, which she said has actually produced some oil.
Activity on east flank
LeFever added that she has seen some recent activity on the east flank of the Bakken which she calls a fringe area because production in that area is not from the Bakken petroleum system. A couple of new cores from that area, she said, show some potential.
While the Bakken is the predominant play, there are other petroleum systems in the Williston Basin, such as the Tyler, the Winnipeg Icebox, the Spearfish in Bottineau County, and the Madison, but LeFever said these other plays are not getting much attention. “Right now everything is pretty much overshadowed by the Bakken,” but she reminded people who are focused on the Bakken that North Dakota has other formations that produce oil. She believes that over the years, once the Bakken is on its way to being well developed, other formations will be evaluated because “I think there is still a lot of oil in our stratigraphic column,” adding that there are 15 formations in North Dakota capable of producing oil. “I think the basin is going to be active for a long time.”
The library
The library is part of the North Dakota Geological Survey, or NDGS, led by State Geologist Edward Murphy. The geological survey is a division of the North Dakota Department of Mineral Resources, and is one of the agencies that functions under the North Dakota Industrial Commission, which is comprised of the governor, attorney general and agricultural commissioner. The geological survey was born out of legislation passed by the North Dakota Legislature in 1895.
It is up to a particular company whether to core, but when core is collected, North Dakota law requires that all core, regardless of well type, be submitted to the library. Cuttings must also be submitted to the library. For wildcat wells, cuttings samples, which are collected at intervals of 30 feet, are submitted from the entire bore from the ground surface to total depth. But if the well is in an active field, the samples are submitted from a particular horizon to total depth. And in addition to the core and cuttings samples, the library also maintains a thin-section collection.
As a result of the requirement that core and cuttings be submitted to the library, LeFever said she believes the library has one of the most complete collections of oil and gas samples in the U.S.
NDGS began collecting samples in 1941, thanks, LeFever said, to the foresight of Wilson Laird, the person for whom the library is named. “We have a very, very complete collection,” she said.
Confidentiality
While it is state law that a company turn over the core and cuttings samples to the library, those samples and the information they contain can be held confidential for up to six months at the company’s request. The six month confidentiality period begins when cores are collected, and at the end of the confidentiality period the information becomes public.
LeFever noted that there a lag period between the times that cores are collected and when they are submitted to the library because the cores first go to commercial geotechnical labs for analysis of such parameters as porosity, permeability and possibly organic content. Consequently, it is not uncommon for cores to be submitted to the lab after the six-month confidentiality period has expired.
The library has many visitors, whom LeFever said come from all over the world, and she has seen people from as far away as Australia and Europe as well as people from domestic oil companies who are active players in the basin. Some, she said, are academics such as a Ph.D. student who came in a couple of years ago from Germany, and some students come in with their advisors to examine the rocks.
Logging samples
The library is located on the University of North Dakota campus in Grand Forks, which LeFever said is fortunate because a large number of UND students are looking for work. She typically has six to eight students who work part time logging samples and photographing core, and two Ph.D. students who are on temporary employee status and are re-boxing cutting and core samples. She said it is a “win, win” situation in that the library has the staff to keep up with the work load and the students have a job. Besides LeFever, there is only one other full-time employee, Kent Hollands, who is in charge of maintaining the collection and managing the student employees.
The students log cuttings samples with such information as well type, location, company name, and the North Dakota license number. This information is then entered into library’s data base, and those samples that are not confidential become immediately available to the public on the North Dakota Oil and Gas Commission’s website. Samples that are confidential are posted for public access as soon as the well is taken off of tight hole status.
When no longer or not confidential, cuttings samples are shelved and available to the public.
The same thing happens with the core. But unlike the cuttings, the cores are photographed before they are shelved, a process the library started some eight to 10 years ago when digital camera technology became readily available. The photographs are processed and posted on the commission’s subscription website.
Depending on the length of the core, LeFever said photographing a core can take from three to six hours. Typically, photographs are available to the public online within one to two weeks after the library has received the core.
Storing core
All of the core and cuttings samples are stored in an 18,000 square foot warehouse that contains row upon row of shelves stacked 10 shelves high, with the bottom eight shelves containing core and the top two containing cuttings.
Core segments are four inches in diameter and up to three feet in length, and the shelves are three feet wide to accommodate core segments. Because of the size of the core, LeFever said they take up a lot of space, but adds that the core “provides a lot of information and that’s the real key.”
The cuttings are stored in boxes specially designed to be 18 inches long so two boxes can fit end to end on each shelf unit, which LeFever said has “saved a tremendous amount of room.” Because cuttings are collected at intervals of 30 feet, a well 18,000 feet deep, for example, will produce four to five boxes of cuttings, according to LeFever.
One problem with storage is that the cardboard boxes currently used to store both the core and cuttings last just so long, LeFever said, especially when they hold 40 to 60 pounds of samples.
The boxes, she said, ultimately break down and will no longer stack, leaving a lot of dead storage space.
The library is currently in the process of reorganizing core and samples into new boxes that stack better than the previous ones. This is opening up a lot of space.
Even as core continues to come in “at an amazing rate,” LeFever said the library is staying ahead of the deluge.
However, she said, ultimately the facility will have to be expanded.
As previously mentioned, in other plays more cores would be collected in the early period of exploration and development and then taper off, but that is not what is happening with the Bakken. She said companies are still cutting large numbers of cores, and she is not seeing a slowdown in the rate at which core comes into the library.
In addition she is now seeing more and more Three Forks core.
Some horizontal cores
While most of the core samples in the library were cut vertically, LeFever said the library has a few horizontal cores. In 1990, she said, Shell drilled a vertical pilot hole from which three horizontal cores were cut, each 30 feet long. Given the technology at the time, LeFever said she thought that was “pretty amazing.”
More recently, she said, SM Energy and Marathon have cut horizontal cores, and EOG cut a horizontal core in the Parshall field that went diagonally through several formations.
All of these cores, which the library has in its collection, were cut at a depth of approximately 11,000 feet.
Using the library
Aside from actually visiting the library, there are several other ways to access the library’s core and sample information.
Core and cuttings sample information and photographs are available on the North Dakota Industrial Commission’s subscription website.
The library will check out and ship cuttings samples, providing there is a sufficient amount of sample to split in order to keep some of the sample at the library. It will also check out thin sections.
All samples must to be returned to the library when the user is finished with them.
LeFever said that when people want to look at numerous wells they will typically visit the library, but if they only want to look at one or two wells, they will usually request cuttings be shipped.
Core samples cannot be checked out, so the only way to view cores is to either look at photographs online or go to the library. While photographs provide what LeFever calls a “nice overview” of core, she said they are not the same as coming to the library and sitting down with the core, which is what a lot of people do.
There is no charge for use of the facility, but the library does charge for shipping samples of cuttings.
If someone wants to photograph cuttings or core samples, the library has the necessary scopes and cameras.
Library also has a lab
The library also has a laboratory that can be used for such things as cutting thin sections and testing for total organic content. But if a company runs tests on any of the library’s samples, it must share its findings with the library.
The time spent studying cores varies, as does the number of people per company. The last person was there for two weeks, she said, and sometimes it can be just one person per company. Other companies may send an entire team of six or seven people.
The library typically allows only one company to visit at a time, and reservations are necessary. It’s currently booking into late November.
In earlier plays, according to LeFever, the library would see a lot of activity in the beginning, when companies would come in and look at rocks, but as the play moved into the development phase, the activity would decline.
In addition, she said, the library would see more activity during the winter months, but activity would fall off in the spring as drilling again increased. With the current Bakken play, however, the activity at the library has been steady from season to season.
