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First White Hills well file public AOGCC well log for Mastodon 3-6-9, drilled in early 2008, becomes public, offering some clues about reservoir and target geology Eric Lidji For Petroleum News
The White Hills prospect has been one of the most active and one of the most secretive on the North Slope in recent winters, with Chevron drilling at least five wells but offering little information about the results of that drilling other than locations and spud dates.
Recently released well data, though, gives a rough sense of the geology and target reservoirs of the second well in the multiyear program, Mastodon 6-3-9.
Chevron, through its affiliate Union Oil Company of California, spud Mastodon on March 3, 2008, and plugged it on March 27 after evaluating it for eight days. “The primary reservoir objectives include gas in the Prince Creek, Ugnu and West Sak formations,” according to a shallow hazards report the company filed in early 2008.
“The Mastodon structure consists of a Northwest-Southeast trending closure with stratigraphic and dip related traps,” the company wrote in the February 2008 report. “The structure is thought to have both permafrost and temperature seals. The structure shows distinctive depositional fairways for sand accumulation based on 2D seismic, surface geology, and magnetic data. The structure sub-outcrops at certain places throughout the field allowing regional correlation between the source rock and target formations.”
Geologic clues suggest both oil and gas targets at White Hills. State officials in 2006 pointed to oil and gas shows in previous wells drilled on the acreage. In late 2008, Marty Rutherford, deputy commissioner of the Department of Natural Resources, said, “This is probably mostly gas, but it is an area where they could also find oil.”
What Chevron isn’t chasing White Hills marked Chevron’s return to the North Slope after nearly 15 years focused on Cook Inlet. The company has declined to discuss targets at White Hills, though, calling it a “tight” venture. According to state regulations, well files become public after two years unless a company gets an extension, like the famous one keeping Chevron’s KIC well in Area 1002 of the Arctic National Wildlife Refuge indefinitely under wraps.
The Mastodon 6-3-9 well files may ultimately say more about what Chevron is not focusing on at White Hills. Files from the two other wells the company drilled that winter — Smilodon 9-4-9 and Panthera 28-6-9 — have still not been released to the public.
The White Hills prospect is on the central North Slope, south of the Kuparuk River unit and just west of the trans-Alaska oil pipeline corridor, including the Dalton Highway.
Mastodon 3-6-9 is in the southern end of the prospect, one of several well locations in the area. Following the first season of drilling, though, Chevron permitted several new well locations farther north, away from Mastodon. Earlier this year the company relinquished much of that southern acreage, including the lease where it drilled Mastodon 3-6-9.
In the files, Chevron also detailed seismic acquisitions, saying it used its position as a working interest owner at Prudhoe Bay and Kuparuk to obtain “as much well data and 3-D seismic as we are entitled to in order to characterize the White Hills area south of the current main producing fields.” Unocal, which acquired the first White Hills leases in 2001, years before merging with Chevron, also acquired 2D seismic. That seismic went through reprocessing in 2002 and 2005. After the merger, Chevron used proprietary technology to “enhance the image in a large swath of low frequency, poor quality data” stretching across the central North Slope, including the northern White Hills area.
In March 2008, Chevron sold a 30 percent interest in its White Hills leases to Total E&P USA Inc. The partners have not detailed future drilling plans for the prospect.
NOTE: A copyrighted oil and gas lease map from Mapmakers Alaska (www.mapmakersalaska.com/) was a research tool used in preparing this story.
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