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Alpine trend shows best NPR-A oil potential, says geologist Ken Bird New USGS assessment says play — from Alpine to the coast — could contain 7 billion barrels of oil, 75 percent of the new estimated mean potential of the reserve Kristen Nelson PNA Editor-in-Chief
The new U.S. Geological Survey assessment of oil and gas potential in the National Petroleum Reserve-Alaska concludes that the federal portion of the reserve contains an estimated mean of 9.3 billion barrels of technically recoverable oil — more than four times the 2.1 billion barrels in the 1980 assessment.
The Alpine field on state land at the eastern edge of NPR-A was the was the key to that assessment, Ken Bird, one of the authors, told PNA May 17.
Bird and assessment co-author David Houseknecht are USGS research geologists.
The most prospective area in the NPR-A for oil discoveries, Bird said, “is basically the Alpine trend: the same interval of rocks that the Alpine field is located in and also the nearby Fiord field,” with estimated means of 5.178 billion barrels in the eastern portion of the play and 1.859 billion in the western portion.
The range for technically recoverable oil from the federal portion of NPR-A is from a 95 percent chance that there are 5.9 billion barrels to a 5 percent chance that there are many as 13.2 billion barrels. The 9.3 billion barrel figure is the mean or expected value, compared to a mean of 2.1 billion barrels in the 1980 assessment.
The range for technically recoverable natural gas in gas fields is from a 95 percent chance of 39.1 trillion cubic feet to a 5 percent chance of as much as 83.2 tcf, and an expected mean of 59.7 trillion cubic feet, compared to 8.5 tcf in the 1980 assessment. Alpine made the difference What changed for USGS between 1980 and the 2002 assessment, Bird said, is “new information from Alpine and the nearby fields.
“We reviewed all the pre-existing information. We did four seasons of additional fieldwork, mostly down in the foothills. We found some very interesting things in those field studies that gave us confidence in projecting into the subsurface.”
The Alpine and Fiord fields are part of a play called the Beaufortian Upper Jurassic Topset Northeast, Bird said.
“It ranges from somewhat shallower to a fair amount deeper (than Alpine). I think Alpine is about 7,000 feet deep and I think the minimum depth for this play is on the order of 6,000 feet and the maximum is probably 10,000-12,000,” with the play becoming deeper as it goes south.
The continuation, the Beaufortian Upper Jurassic Topset Northwest, is still Alpine, just farther west. “We know a fair amount less about it out in that area,” Bird said, “because of relatively few well penetrations.” Details about Alpine from Phillips The USGS did not have access to 3-D seismic from Alpine, but Bird said they did have access to details about the Alpine field from an article field operator Phillips Alaska Inc. published “showing the seismic character of it.”
“We had access to virtually all the wells in the Alpine field and nearby and we were able to put that together into a geologic model and then we could relate it to the interval that we can see in 2-D seismic.”
“We can see the gross interval that is represented by Alpine” on the 2-D seismic that USGS has over NPR-A, Bird said.
“In fact, we can see even some details that we think show some interesting leads that might relate to Alpine-type accumulations,” he said.
The Alpine sandstone averages about 50 feet thick, “pretty thin to see on seismic data. But we are able to map the limits of the gross interval that contains Alpine. And that was the basis for drawing these play boundaries,” Bird said.
Meltwater, Tarn, Nanuq shallower, younger The other most prospective areas, 1.306 billion barrels and 0.973 billion barrels, are comparable to Nanuq, Meltwater and Tarn, Bird said.
This is a shallower, younger horizon, he said. “They’re subtle stratigraphic traps — that is they’re difficult to see if you don’t have 3-D seismic.” These plays are the Brookian Clinoform North and the Brookian Clinoform Central.
“Based on the mean estimate,” Bird and Houseknect said in the assessment, “about 80 percent of the technically recoverable oil resources are likely to occur in northern NPR-A within plays that are westward continuations of the geologic trends that host Alpine, Fiord, Tarn, Meltwater and Nanuq oil pools, just east of NPR-A.” No new Prudhoe The Alpine play is on the flank of the Barrow Arch, Bird said. “The Barrow Arch is the high area beneath the coastline and most of the rocks in that area dive to the south and become much more deeply buried.”
The Barrow Arch is the feature responsible for most of the oil fields along the northern coast of Alaska, Bird said.
“The oil tends to migrate through the rocks to high, relatively high positions. And the Barrow Arch is the regional high and that’s why you see all the oil strung out along there.”
The coastal area from Teshekpuk Lake north is off limits in the northeast NPR-A area, the area first leased in 1999 and coming up for lease again in June.
Bird said the area was included in the current evaluation.
“And this is the area where one would think that you’d look for another Prudhoe Bay,” Bird said. It was where the Navy drilled in 1974-75 “looking for Prudhoe Bay-type accumulations,” he said. “And it turned out that the conditions were not quite right.”
There is oil in the area, Bird said, and it was encountered in many of the wells drilled both by the government and by industry offshore.
“That’s where Mukluk is located. And a number of other wells a little to the west of Mukluk were all targeted for this Prudhoe Bay-type accumulation, so that our evaluation now is that this has been pretty thoroughly tested for Prudhoe-type accumulations, so that’s why you don’t see any big Prudhoe-type oil fields showing up in our evaluation.” Oil will be expensive to develop Although the oil potential of NPR-A has more than quadrupled in this assessment, to some 9.3 billion barrels, the USGS assessment said the amount of economically recoverable oil is significantly less, and at $20 a barrel is believed to be zero. At $40 a barrel, 6.9 billion barrels would be economic.
For this fiscal year, the Alaska Department of Revenue expects the price of ANS crude oil to average $21.50 a barrel, which would make less than 1 billion barrels economically recoverable.
The Arctic National Wildlife Refuge coastal plain, at 1.9 million acres (1.5 million of that federal acreage) is more economic partly because it is more compact. The entire NPR-A is 24.2 million acres (22.5 million federal acres).
The USGS estimates that, like NPR-A, the ANWR coastal plain has no economically recoverable reserves at $15 a barrel. But starting at $20 a barrel, ANWR is estimated to have 3.2 billion barrels of economically recoverable oil. Economics tough Bird said that the NPR-A economic analysis was based on the expected size of accumulations — basically nothing larger than 1 billion barrels and most accumulations in the 32 million to 256 million barrel range — and the distance from infrastructure.
“The northeastern area is going to have better economics because of its proximity to the infrastructure,” he said.
“We’re looking at where would you have to build a pipeline to get the oil out of NPR-A. And right now the Alpine pipeline is full to capacity and they’re trying to expand that capacity. And so that means that if you find something in NPR-A, you’ve got to build a separate pipeline from those discoveries all the way to Kuparuk.”
With no spare capacity in the Alpine pipeline, you have to build pipeline to the edge of the NPR-A and then the additional 30-some miles to Kuparuk, he said.
“And that’s just for the northeastern area. The farther west you go — if you found something out in the very western part of NPR-A you’re 300 miles from Kuparuk.
“So it’s an enormous economic disincentive, I guess is the way to put it,” Bird said. Distance and size Distance from Kuparuk is built into the economic model.
“The farther you go away from the infrastructure, the larger the field would have to be in order to make it economic,” he said.
Bird said the analysis was done for a series of sub-areas. The NPR-A was divided into blocks and a center point was designated for each block.
Calculations were done from that center point on what the cost would be to build a pipeline, based on the distance to Kuparuk from the central point for the area, and the costs of drilling and pad development.
“And so the farther west you go into NPR-A, the more expensive it’s going to become.”
In addition to the size of the accumulation, Bird said, the nature of the reservoir and how much of the oil you could produce also figure into the economics.
“But once you have found something and built a pipeline to it, then that changes the economics. Just like around Alpine, you’re seeing all these satellite developments that are suddenly possible now that you’ve got the infrastructure there.”
It took Alpine, Bird noted, to make the smaller Fiord accumulation commercially attractive.
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