|
THE EXPLORERS 2004: The search for Cook Inlet’s ‘missing giants’ Independent Escopeta Oil shopping offshore Alaska prospects, using new seismic technology Petroleum News
The U.S. Department of Energy’s recently published report on Alaska Cook Inlet natural gas hypothesizes that there are missing giants — large oil and natural gas fields that remain to be found in Cook Inlet.
Houston-based independent Escopeta Oil, one of the inlet’s largest state oil and gas leaseholders, thinks it has identified two of these missing giants in its Kitchen and East Kitchen prospects. The company is looking for a partner so that it can bring in a jackup rig to drill an exploration well.
Escopeta President Danny Davis told Petroleum News in July 2004 that the company hopes to have partners in place in time to begin permitting this fall and bring a jackup rig to the inlet next year to drill the prospects, which are offshore the Kenai Peninsula, north of Nikiski.
Ten years of work The Kitchen and East Kitchen prospects are in 70 feet of water close to the Kenai industrial complex. They represent 10 years of work by the company, including studies by geologists with Cook Inlet experience and, more recently, the reprocessing of seismic by Houston-based Apex Metalink Inc. with its proprietary technology.
How could there be missing giants in Cook Inlet, a hydrocarbon basin which has been in production for nearly 50 years?
“There were always a few questions that were unanswered when we were doing work in the inlet, in relation to the fields,” said Bob Warthen, a consulting geologist working with Escopeta. Warthen has worked the inlet since 1967, first for Union Oil where he was a regional geologist for 26 years, and then as a consultant.
“And after Prudhoe Bay was discovered, the inlet became a stepchild, so the working scenarios in the inlet were strictly a development-type scenario. … Consequently very little exploration work has been done,” he said. .. Then you had the oil problems in ’85 and ’86 — the oil price collapse; then more restructuring; then you had company mergers.
“I’m probably one of the few guys left working the inlet that started in the early days,” Warthen said.
The ‘play book’ After Warthen took an early retirement from Unocal in 1992, he began working all the available data on the inlet, including well information and seismic, and looked at rocks, trying “to get a better understanding of the intricacies of the formations.”
And he developed a basin map, “let’s just call it an idea map, or as Danny (Davis) calls it, our ‘play book’,” he said.
That idea map, in different iterations, identified acreage acquired by Escopeta, which began looking for opportunities in Alaska in 1993 and bought its first leases in the state in 1994. The company now owns some 128,000 acres of oil and gas leases in the Cook Inlet basin.
Reevaluating Cook Inlet The work Warthen originated on the inlet was focused on the petroleum system and potential untested habitats and traps for hydrocarbons. In addition to Warthen, geologists Walter Wells and Frank Banar, retired from Mobil, contributed to Escopeta’s “idea map,” hiring on as consultants for Escopeta.
“Reservoir rocks are not a problem in Cook Inlet: every horizon has reservoir rocks with varying porosities and permeabilities that are basically reasonable,” Warthen said. “Trapping was not really a problem either,” since available seismic provides “a decent understanding of the style of traps and accumulation mechanisms.”
Walter Wells did a search for everything written on the petroleum systems in the inlet, Warthen said. “When we started looking at the three things that you need for a prospect — the trap, the reservoir and the charge — we started really focusing on the petroleum system, on the migration path, the generating area, and we looked at a lot of the seminal USGS reports from some of the real experts in that field, and even interviewed some of them.”
The theory on migration of oil, Warthen said, is that the migrating oil finds a path, and then travels along that path, not deviating from it.
“When it leaves the source area, it migrates up dip and fills the deepest traps first,” he said. “As these are filled the oil continues to migrate up dip filling the shallowest traps in turn.”
Only 4% of oil identified U.S. Geological Survey had theorized that only 4 percent of the volume of oil that theoretically generated from Cook Inlet source rock has ever been identified.
Some of the oil could have leaked out of the basin, Warthen said. And there has been a theory that the basin tilted and the oil remigrated. If the basin tilted, he said, some traps would be pretty well filled and others are going to be only 15-20 percent filled.
But the known traps are filled between 58 and 65 percent, except Middle Ground Shoal, which Warthen said was filled 80 to 85 percent.
The Escopeta acreage position at Kitchen and East Kitchen is “just to the east of Middle Ground Shoal and situated directly overlying the Tertiary/Mesozoic depocenter and we believe the early oil is migrating in an east-west direction,” Warthen said.
Because of the known migration path of oil in the inlet, it is believed that oil migrated into the Kitchen prospect traps, filled those, and subsequently migrated on to Middle Ground Shoal and then into other fields, and “that’s the reason why Middle Ground Shoal is about 80 to 85 percent filled and the rest of these (farther along the migration path) are less (filled),” Warthen said. “We believe that these prospects are among the missing giants postulated by the U.S. Department of Energy,” he said.
“We kept referring to this area here as the area where the oil was ‘cooked’, i.e. being the ‘kitchen’” – hence, the names Kitchen and East Kitchen, Warthen said.
Reprocessing and remapping Escopeta has purchased seismic from a number of companies and used those lines to delineate the area, to look at the prospect from “a structural standpoint,” Warthen said.
The company has had the seismic lines reprocessed and, based on that reprocessing, remapped the Kitchen complex area.
The southern part of the prospect that contains East Kitchen has never been identified, Davis said, “and this feature extends another eight miles beyond the original tested anticline.” The South Cook Inlet anticline has been remapped and is now “about 15 to 16 miles long and about three to four miles wide,” he said. The Shell SRS No. 1 well on the northern flanks tested 360 barrels of oil per day from a lower Tyonek sand, he said. Other prospective pays were never tested due to collapsed casing.
“The southern half of the anticline is what we’re calling our East Kitchen prospect, and it has never been drilled. In effect, it is a major anticline with demonstrated hydrocarbons that have not been adequately tested,” Davis said.
So what do the combined studies indicate to Escopeta about potential Kitchen and East Kitchen reserves?
Escopeta consultants estimate potential reserves at East Kitchen as 2.33 trillion cubic feet of gas and 457 million barrels of oil, Davis said. For Kitchen the numbers are 3.95 tcf of gas and 829 million barrels of oil.
A new processing technique Banar said one very important thing Escopeta did was to have the data reprocessed using a process called wavelet energy absorption, which has been used in Asia, West Africa and Siberia. In China, he said, the process was used in basins which have both coal and gas, and where the gas needed to be identified on the seismic.
Because Cook Inlet has both coal and gas, the process seemed appropriate, he said. In addition to the seismic processing for gas, Apex Metalink also has a process for fluids identification.
The wavelet energy absorption processing “showed some significant gas reserves on the Kitchen and East Kitchen structures, especially in the Tertiary section, where abundant coal beds have generated major dry gas reserves,” Banar said.
Current Cook Inlet production is from Tertiary formations: dry gas from Sterling, Beluga, and upper Tyonek; oil from the lower Tyonek and Hemlock. There is no production from the older Cretaceous and Jurassic in the upper Cook Inlet basin, although surface oil seeps are known from the Jurassic Tuxedni formation. The Tuxedni, said Warthen, has been identified by the USGS as the source rock for all of the oil present in the Hemlock.
Davis said potential deep gas below the Tertiary is a separate prospect. The objectives at Kitchen and East Kitchen are the major producing Cook Inlet formations, the Sterling, Beluga, Tyonek and Hemlock. Escopeta does not attribute any reserves to pre-Tertiary, he said, but considers them a very viable future target.
One of the things the Department of Energy report says is that the inlet has been explored for structural traps but not for stratigraphic traps. “There was no concentrated exploration for stratigraphic-type plays or potential below where they’ve found everything in the Hemlock (formation).” East Kitchen is a structural trap, he said, while Kitchen is a faulted stratigraphic trap first proposed by the USGS.
Matches DOE’s hypothesis What Escopeta is doing matches up with the Department of Energy report’s description of two-phase exploration history in mature basins, first exploration for structural traps like the company’s East Kitchen prospect, Davis said, and then a second phase focused on stratigraphic plays like the company’s Kitchen prospect.
“At this point in time Cook Inlet exploration is still in the structural prospect phase,” he said. “Few if any exploration plays have been pursued and drilled solely on stratigraphic trapping concepts. Based on exploration results in basins elsewhere, this implies as much as 50 percent or more of the basin’s reserve potential has not been investigated,” Davis said.
| 