Denver company taking a fresh look at old seismic data
Although the first new oil is yet to flow, the apparent recent successes of several companies exploring on the North Slope has at least a few people looking for new clues in old geologic information that covers a large swath of the oil and gas basin.
Geologist Bill Enyart and his Denver-based company Seismic Strategies have applied modern processing techniques to approximately 1,000 miles of the roughly 15,000 miles of two-dimensional seismic data shot across the National Petroleum Reserve-Alaska.
The 23 million-acre federal NPR-A covers nearly the entire western half of the North Slope. The eastern portion of the reserve nearest to existing oil infrastructure is a focal point for Slope oil exploration after Torok and Nanushuk formation discoveries by ConocoPhillips in the NPR-A and Armstrong Energy and Caelus Energy on adjacent state acreage.
ConocoPhillips’ Willow prospect, announced in early 2017, has the potential to produce upwards of 100,000 barrels per day, according to the company, as does Armstrong’s original Nanushuk discovery in the Pikka Unit on state lands just to the east of the reserve. Both of those finds centered on the shallow, conventional Nanushuk formation, are being permitted for development.
Oil Search, an Australian producer, took over operations of the Pikka Unit last year after a $400 million deal with Armstrong announced in fall 2017.
Caelus’ similarly large Smith Bay prospect in state waters on the northern edge of the NPR-A is focused on the Torok formation, which is geologically related to the Nanushuk.
Those discoveries also led the U.S. Geological Survey to drastically increase its oil resource estimate for the reserve and nearby state lands in late 2017 to more than 8.8 billion recoverable barrels.
Enyart said the NPR-A 2D seismic data was shot by federal agencies, including the Navy, in the 1970s and 80s. The NPR-A was first established as a Naval Petroleum Reserve in 1923 and was later transferred from the Navy to BLM.
He described the original seismic as “a very good data set” that would be difficult to duplicate today, primarily because of cost and environmental considerations.
Given that, the mere fact that it exists makes the old information valuable today, he said.
“The signal’s there but since that data was acquired we have seismic data processing routines that can extract additional information and those routines just weren’t available 40 years ago,” Enyart said.
Very simply, when geologic seismic data is shot, sound waves are sent into the depths of the Earth and when those waves return — in a basic sonar process — they provide information about the type and formation of rocks beneath the surface as well as the possibility of hydrocarbon deposits.
New seismic reprocessing technology provides higher resolution images and can better organize old sound signals that were disrupted by permafrost, which can scramble seismic signals.
“The original process was just broad-brush processing looking deep into the section. Historically, a lot of the production was coming from older, deeper formations, so we put a lot of effort looking into the (often shallower) Cretaceous rocks, that would be the Nanushuk and Torok formations,” Enyart said, adding that he’s not aware of anyone else doing this work on the NPR-A data.
While the Slope is generally considered a vastly underexplored oil and gas basin, such reprocessing can help identify previously overlooked prospects even in heavily covered areas such as the Gulf Coast, according to Enyart.
He acknowledged that most oil companies today won’t commit to drilling an exploration well — which on the Slope can cost $20 million or more depending on the remoteness of the location — without first seeing modern 3D seismic data of the target, but said an updated version of the publicly available 2D data is a good starting point for companies interested in Alaska.
“The downside to 3D is it’s an expensive means of acquiring seismic data and 2D is a good reconnaissance project,” Enyart described. “You go into an area the size of the NPR-A and shoot 15,000 miles of 2D seismic — that gives you clues as to the broad geology. It gives you an idea of what it looks like below the surface in kind of a gross or coarser sense and then that allows you to zero in on choice areas and go out and acquire 3D for finer prospecting.”
Similar reprocessing could be done on “tax credit” seismic data shot on state lands that is becoming publicly available because it was shot with the financial help of the state’s former refundable oil and gas tax credit program, according to Enyart.
Companies that use the seismic tax credit program were able to get state support for the work in exchange for agreeing to make the data public after 10 years.
Alaska Division of Oil and Gas geophysicist Holly Fair said reprocessing old seismic is a basic way to add value to what is already publicly available.
Geologist Kevin Frank, head of the Oil and Gas Resource Evaluation Section, added that seismic shoots on the North Slope must be done when the tundra is frozen, which limits the ability to acquire the data.
A planned 3D seismic shoot over the newly-opened for exploration portion of the Arctic National Wildlife Refuge had to be scratched this winter after the government shutdown delayed permitting for the work, Frank noted.
“If you just cannot get — even if you’re indifferent to cost — you cannot get new data, you work the old data to your benefit,” he said.
Some seismic was shot on the ANWR coastal plain by a consortium of companies in the mid-1980s, but it generally remains proprietary information.
Elwood Brehmer can be reached at [email protected].