Find Draws Illinois Basin Attention

Reef Play Puts Mature Area In New Light

Just on the outskirts of Stephen A. Forbes State Park in Marion County, Illinois, a high-tech oil well nestled on secluded land owned by the First United Methodist Church of Kinmundy is making history.

The discovery well has tapped what appears to be the largest modern oil find in Illinois — and perhaps the largest per area discovery in the state's history.

And perhaps even more importantly, the discovery could touch off a new era of drilling in the mature Illinois Basin.

This new field is a Silurian pinnacle reef structure, and it's likely there are additional reefs hidden beneath the traditional shallow production throughout the basin, according to Charles W. Wickstrom, vice president of exploration for Tulsa-based Ceja Corp.

Ceja's exploration niche focuses on plays that require seismic, and the firm first went to Illinois in 1978 using deep- hole dynamite seismic acquisition techniques in its search for Silurian reefs, but the only bright spot in the effort was the discovery of the Miletus Field, a shallow Mississippian-age field that has produced for years and is currently on secondary recovery.

For the Silurian play, after 13 dry holes the company decided to move on.

Now, more than 20 years after Ceja first sought Silurian reefs in Illinois, the company has firmly established the impressive potential of these structures.

Wickstrom, who rejoined Ceja in 1995 after a nine-year hiatus, began reprocessing with new technologies and techniques all the firm's old seismic data.

"This reprocessing program imaged a deep structure under the Miletus Field that we had been unable to see before — with the new processing techniques the reef structure is very obvious," Wickstrom said. "In 1996 we deepened an existing well in the field to test the reef, and that well produced about 70 barrels of oil a day."

Following that well, Ceja acquired an eight-square-mile 3-D survey over the field and began developing the deeper structure.

Ceja has drilled 15 wells to that deeper reef in the Miletus Field, with development still under way. The firm is producing 2,000 barrels of oil a day from the 320-acre reef, and ultimate reserves will likely be five to six million barrels of oil.

Wickstrom said the new production was so economic that during the last 1990s price collapse the field was a financial savior.

"We are developing the field in a manner that will conserve as much reservoir energy as possible," he said, "depleting the reservoir from the bottom up to maximize ultimate recoveries."

First Steps

That deeper Miletus production is impressive, but perhaps the most important element of that venture is the experience and confidence it gave Ceja to renew its search for Silurian reefs.

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Illinois basin map

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Just on the outskirts of Stephen A. Forbes State Park in Marion County, Illinois, a high-tech oil well nestled on secluded land owned by the First United Methodist Church of Kinmundy is making history.

The discovery well has tapped what appears to be the largest modern oil find in Illinois — and perhaps the largest per area discovery in the state's history.

And perhaps even more importantly, the discovery could touch off a new era of drilling in the mature Illinois Basin.

This new field is a Silurian pinnacle reef structure, and it's likely there are additional reefs hidden beneath the traditional shallow production throughout the basin, according to Charles W. Wickstrom, vice president of exploration for Tulsa-based Ceja Corp.

Ceja's exploration niche focuses on plays that require seismic, and the firm first went to Illinois in 1978 using deep- hole dynamite seismic acquisition techniques in its search for Silurian reefs, but the only bright spot in the effort was the discovery of the Miletus Field, a shallow Mississippian-age field that has produced for years and is currently on secondary recovery.

For the Silurian play, after 13 dry holes the company decided to move on.

Now, more than 20 years after Ceja first sought Silurian reefs in Illinois, the company has firmly established the impressive potential of these structures.

Wickstrom, who rejoined Ceja in 1995 after a nine-year hiatus, began reprocessing with new technologies and techniques all the firm's old seismic data.

"This reprocessing program imaged a deep structure under the Miletus Field that we had been unable to see before — with the new processing techniques the reef structure is very obvious," Wickstrom said. "In 1996 we deepened an existing well in the field to test the reef, and that well produced about 70 barrels of oil a day."

Following that well, Ceja acquired an eight-square-mile 3-D survey over the field and began developing the deeper structure.

Ceja has drilled 15 wells to that deeper reef in the Miletus Field, with development still under way. The firm is producing 2,000 barrels of oil a day from the 320-acre reef, and ultimate reserves will likely be five to six million barrels of oil.

Wickstrom said the new production was so economic that during the last 1990s price collapse the field was a financial savior.

"We are developing the field in a manner that will conserve as much reservoir energy as possible," he said, "depleting the reservoir from the bottom up to maximize ultimate recoveries."

First Steps

That deeper Miletus production is impressive, but perhaps the most important element of that venture is the experience and confidence it gave Ceja to renew its search for Silurian reefs.

"The Miletus Field is just north of the Stephen A. Forbes State Park, and we had always been interested in shooting seismic over the park but had been denied surface access," Wickstrom said.

But since the company's first efforts in the 1970s the state of Illinois consolidated its Department of Mines oil and gas division into the Department of Natural Resources (DNR), which provided a level of expertise about oil and gas operations with the DNR.

"Consequently, we were able to convince state officials to allow us to shoot seismic along an existing abandoned pipeline right-of-way through the park," Wickstrom added.

Ceja shot the 2-D seismic in October 2000 and the data imaged part of a deep structure. While discovery of the structure was exciting, it was still under a state park where no oil and gas operations were allowed.

Ben Webster, president of project partner Deep Rock Energy, had a local attorney do a title and deed research in the area. He uncovered over 140 private mineral leases still held by individuals that the state failed to condemn when the park was established.

A joint venture between Deep Rock Energy as the operator and Ceja's managed partners was established and Ceja leased those mineral rights. The company then went to the DNR and requested that the state do a voluntary integration of the state's mineral interests with its private ownership with the stipulation that it would do no surface occupancy within the park.

"The DNR also granted permission to shoot 3-D seismic in the park," Wickstrom said, "as long as we didn't cut down any trees larger than six inches in diameter."

A Team Approach

Ceja's own seismic crew shot 90 percent of the eight-mile 3-D seismic survey using hand carried cables and a single vibrator truck along the extensive horse trails and existing rights of ways in the park. The data successfully imaged the reef under the park and the 585-acre lake in the park.

"With that data in hand we had public hearings and presented our information to the state," Wickstrom said. "Officials agreed to form two special drilling units — one north of the park and one southwest of the park."

Of course, the stipulation to not drill on park land meant horizontal drilling technology was necessary. However, to obtain additional downhole information prior to attempting an expensive horizontal well the joint venture re-entered an old well 300 feet north of the park on acreage held by shallow production that was part of the original development of the Miletus Field.

"Based on the 3-D seismic data we knew we had a reef similar to the one just north in the Miletus Field," he said. "However, we didn't know whether we had porosity or oil.

"We could see that part of the reef extended just beyond the edge of the park boundary where we had an old shallow well," he said. "We re-entered that old well to get a true top on the structure and to get a good velocity to depth."

Ceja was able to core the zone to determine that we did indeed have reef rock and there was oil present.

"That well was completed producing 400 barrels a day for $300,000," Wickstrom added, "and it gave us a lot of confidence prior to drilling a $1.5 million horizontal well."

Deep Rock and Ceja assembled a team of experienced companies to work on the horizontal project:

  • Les Wilson Drilling out of Indiana provided the iron.
  • Oklahoma City-based Baker Hughes Inteq was contracted as the horizontal-drilling experts.
  • Weatherford Controls brought a crew from Canada to aid in drilling the well under balanced.

The partners knew under balanced drilling was going to be important based on unsuccessful drilling by other companies. A horizontal well drilled into a reef under Carlisle Lake in Illinois on federal leases did not drill under balanced, and when the well drilled into the reef it was so porous it took all the mud, leaving no fluid in the hole.

The operator wasn't ready for the oil that started flowing.

"We set our intermediate casing through the curve to within a foot of penetrating the reef using mud," Wickstrom said. "We then took the mud out of the hole and using diesel drilled out into the reservoir. That should have kept us at about 40 pounds under balanced, but cuttings kept the weight of the diesel over pressured, so we were able to drill only about 220 feet into the reef before we started getting a lot of cuttings built up in the hole."

The drillers attempted to reduce the weight by injecting nitrogen into the hole, but as soon as nitrogen came back to the surface the well started flowing gas and oil.

Deep Rock and Ceja decided to terminate the Warren No. 1 at that point since they were getting impressive oil flows from the Geneva B formation.

"We only drilled 220 feet into the reservoir, but we had such prolific production tests that we decided to stop," he said. "The well was completed in March for 2,000 barrels of oil a day flowing, but production is currently up to 3,000 barrels daily and it is choked down."

It was drilled from the northeast corner of the field with a total vertical depth of 3,850 feet and a measured depth of about 5,000 feet.

Going Out

Following the success of that well the companies moved to the southwest corner of the park and re-entered an old well. The Carter No. 1 achieved a 400-foot horizontal leg in the Geneva B pay zone and is currently awaiting construction of a tank battery.

"We drilled that well under balanced the whole way, so we were actually producing oil and gas on a controlled basis while we were drilling, Wickstrom said.

"We have run a production test and this will be another prolific well."

Illinois law limits drilling to one well per horizon on special drilling units, so these will be the only two wells to the Geneva B. The joint venture will now move to the field's northwest corner (Warren special drilling unit) and the east side on the Carter special drilling unit and drill to the Geneva A.

Both wells will have half-mile long horizontal legs.

Currently Deep Rock Energy and Ceja are conducting reservoir and reserve analysis studies, so there is no published reserve figure for the reef — but Wickstrom said this will be a multi-million barrel field.

Ultimate life of the field is expected to be five to 10 years. Rock Creek Energy and Ceja also are conducting shut-in pressure tests and draw down pressure tests on the two wells to determine the most efficient means of production to maximize ultimate recovery.

"We want to make sure we keep a low pressure draw down across the wellbore so we're not over producing the reservoir," Wickstrom said. "We've seen in other areas of the basin where companies have tried to produce too fast, and it's been detrimental to the reservoir."

The two companies are getting more comfortable with the horizontal technology.

"Keeping the drilling fluid under balanced was the key to getting further out on the second wel,l and we have continued to move up the learning curve," he said.

In addition to traditional horizontal drilling tools such as measurement while drilling and geosteering, the seismic data has been critical in the drilling process.

"Landing the horizontal leg precisely within these relatively thin zones is vital," he said. "We loaded the 3-D seismic data on a laptop, and using seismic vision systems we can assess the location of the drillbit in relation to the structure maps.

"As you pick up new drill tops, you can correct the seismic to the actual drilling depth, helping to hit a target that's only six feet wide."

The Beautiful Stacked Pays

Ceja will be acquiring a high-resolution 3-D seismic program later this year to better delineate the reef structure.

"During the initial 3-D survey we were constrained by the line spacing," Wickstrom explained. "We have developed a good working relationship with the park's management and this time plan to use closer lines, more channels and a bigger system so we can image the shallower horizons."

Each of these special drilling units may have six to eight different productive horizons.

"These stacked pays are the beauty of the Illinois Basin," he continued. "They saved us years ago at the Melitus Field, where we drilled deep but found shallow pay that held all the acreage until we had the technology to image the deeper formations."

The two companies also are looking at various ways to capture the field's significant associated gas stream to fuel the micro-turbines that are being installed for energy needs at the wellsites. They're also working with the local utility on a deal that would provide electricity to the park.

"We can stack these micro-turbines side by side and generate 30 kilowatts per hour per each micro-turbine," Wickstrom said. "This way we can use this resource rather than flare the gas."

Ceja's success in the two deeper Silurian reefs could spur renewed interest in the hunt for deeper reefs throughout the Illinois Basin.

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