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Providing coverage of Alaska and northern Canada's oil and gas industry
July 2019

Vol. 24, No.28 Week of July 14, 2019

Airborne surveys over ANWR 1002 unlikely but USGS still releasing new geologic data prior to lease sale

Kay Cashman

Petroleum News

With SAExploration’s 3D seismic survey delayed until next winter, there will be less data about the geologic potential of the ANWR 1002 area available to bidders in the federal lease sale later this year.

“The latest news indicates that an airborne gravity gradiometry survey, which has been discussed by at least two vendors, seems unlikely this summer. So, only those companies that co-own the vintage 2D data will have any subsurface data,” USGS senior research geologist Dave Houseknecht told Petroleum News July 10.

The agency has completed a grounds-up reprocessing of 1,451-line miles of vintage 2D seismic data collected from the ANWR 1002 area in 1984 and 1985. The purpose was to tease out more detail than was apparent in the initial data.

The 2D survey was funded by a consortium of companies led by Exxon. The 11 that are left are Anadarko, BP, Chevron, ConocoPhillips, ExxonMobil, Hess, Marathon, Murphy, Oxy, Shell and Total.

Houseknecht was hoping the reprocessed data would be available to them, but the U.S. Department of Interior’s Office of the Solicitor “has determined that the USGS is not permitted to make the reprocessed 2D data available to any companies, including those that own the rights to the original raw seismic data,” he said.

But there is other information that USGS is releasing to the public.

“Our seismic interpretations … are focused on reducing critical geological uncertainties. We are not permitted to show or publish images of the reprocessed ANWR data, so our public presentations use analogs from offshore (ANWR 1002) and state lands west of the Canning River. In both areas, we are permitted to show images of seismic data that we have licensed from certain seismic companies,” Houseknecht said.

Field work results

Led by Houseknecht, the USGS has conducted field work in and near the ANWR 1002 area during the past two summers, with a particular focus on oil-prone source rocks, geochemistry of oils from oil-saturated outcrops and nearby wells (including the Stinson and Kuvlum discovery wells), distribution and quality of potential reservoir rocks, and structural evolution of the area.

When asked to comment on the most important information released in recent presentations, Houseknecht said, “The presence of Triassic (Shublik Formation) and Jurassic (Kingak Shale) source rocks is a significant uncertainty in the 1002 Area. Those units are truncated by the Lower Cretaceous Unconformity across a large part of the northeastern North Slope as indicated by well penetrations and seismic data east of Prudhoe Bay and by outcrop data in the Sadlerochit Mountains. The Triassic and Jurassic source rocks may be present in northeastern 1002 Area if they are preserved in graben basins. Regardless, the presence of a thick (up to 200 meters) and rich (up to 26 weight percent total organic carbon) Brookian source-rock interval is known in the 1002 Area from outcrop studies.”

“And, in the eastern 1002 Area those Brookian source rocks were imbricated by Cenozoic thrust faults. In that area, the source rocks have immature thermal maturity values in outcrop and are modeled to be in the oil window in the subsurface. Thus, the Brookian represents a viable, oil-prone source rock that could charge both stratigraphic and structural in the 1002 Area,” Houseknecht said.

A summary of this information was presented at the AAPG Convention in May and will be posted on the AAPG Search and Discovery website later this summer.

- KAY CASHMAN






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