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Explorers 2011: Doyon: Interior basins show promise New evidence suggests Nenana basin much deeper than previously thought, as deep as 25,000 feet Alan Bailey Petroleum News
New geophysical and geochemical investigations in the Nenana and Yukon Flats basins in the Interior of Alaska have pointed to a high resource potential in both of these basins, James Mery, Doyon Ltd. senior vice president, lands and natural resources, told Petroleum News on Sept. 8.
Investigations completed in the past couple of months have indicated that the Nenana basin is much deeper than previously thought, while rock samples recovered from the Nunivak No. 1 well near the town of Nenana show the presence of hydrocarbon source rocks, potential sandstone reservoirs and shales that would form effective hydrocarbon seals. Parallel research in the Yukon Flats basin has provided tantalizing indications of oil and gas in the subsurface, and of subsurface structures that could trap hydrocarbon resources, Mery said.
Seeking opportunities For several years Doyon, the Alaska Native regional corporation for much of the Interior, has been seeking new resource development opportunities within its region, hoping to make profits for its Native shareholders while also providing local employment. Doyon subsidiaries that provide services to the oil and gas industry also stand to gain from new commercial developments in the Interior.
A partnership consisting of Doyon, Rampart Energy Co., Arctic Slope Regional Corp., Usibelli Energy LLC and Cedar Creek Oil & Gas Co. has been conducting an exploration program in the Nenana basin, about 50 miles southwest of Fairbanks, seeking natural gas and possibly oil. The partnership drilled the 11,000-foot Nunivak gas exploration well in 2009 but that well did not encounter an economic gas accumulation.
New seismic Doyon has taken over as operator of the Nenana basin exploration program and plans to acquire some 2-D seismic in the northern part of the basin between January and March 2012. The Nenana partnership acquired seismic data for the more southerly part of the basin in 2004 and 2005. Much of the exploration is taking place on state land, under the terms of a state exploration license.
In the Yukon Flats, a 15,000-square-mile lowlands area around the Yukon River, between the trans-Alaska oil pipeline and the Canadian border, Doyon has been investigating the resource potential within Native lands, where the corporation and its shareholders would potentially gain royalties from oil and gas production, in addition to realizing the other potential economic benefits from new resource development.
Both the Nenana basin and the Yukon Flats basin consist of huge depressions in the Earth’s crust that have resulted from movements along major geologic faults and that have become filled with river- and lake-borne sediments, primarily of Tertiary age. Prolific vegetation once growing in these landlocked basins has over time given rise to an abundance of coal seams within the rock sequences.
Borrowing successful exploration strategies from analogous basins elsewhere in the world, Doyon has licensed whatever existing geophysical data are available for the basins, acquired new data and also done some surface geochemical sampling, seeking surface traces of subsurface hydrocarbons, Mery said.
Nenana basin For the Nenana basin, the corporation has licensed seismic data acquired by Shell in the 1980s, as well as using its own more recent data. The merging of seismic data with proprietary gravity and magnetic data that the corporation has also obtained under license, combined with new data from the Nunivak well, has enabled a new assessment of the basin subsurface. That assessment points to much greater depths with the basin than were indicated by earlier work, and the existence of a previously unknown arch-shaped structure in the base of the northern part of the basin.
“We’ve concluded that the basin is much deeper than anyone previously thought,” Mery said. “Some parts of the basin could be as deep as 25,000 feet.”
New well data also indicate that the basin is a bit cooler than data from some old wells on the basin margins had suggested, although the temperature gradient within the basin is fairly typical for a continental interior situation, with the deeper sections of the basin likely to be within the appropriate temperature range for oil generation.
Excellent source rocks Analysis of coal samples recovered from the Nunivak well shows excellent hydrocarbon source potential, including the presence of material that would support the generation of both natural gas and oil, Mery said. Intriguingly, some well cuttings also contained hydrocarbons with molecular weights higher than that of the methane that is the primary component of natural gas, presumably suggesting the generation of some hydrocarbons from the heating of source rocks, rather than from the bacterial decomposition of organic debris.
Geochemical analysis of some near-surface soil samples above the basin has shown trace quantities of a similar hydrocarbon mix, Mery said.
Yukon Flats In the Yukon Flats Doyon is interested in both the oil and the gas potential of some sub-basins of the main Yukon Flats basin, with some of those sub-basins lying not too distant from the trans-Alaska oil pipeline. One of the sub-basins is near the village of Stevens Creek where Doyon’s recent surface sampling and geochemistry has detected traces of oil and natural gas liquids that would, again, have been formed from a thermal process. These types of surface hydrocarbon trace are particularly prevalent over another sub-basin around the village of Birch Creek, where Doyon has also done sampling and hydrocarbon analysis of deep mud in lakes, Mery said.
And Doyon’s most recent interpretation of gravity, magnetic and seismic data for the Birch Creek sub-basin shows subsurface geologic structures that could have trapped oil or gas.
“It sets up a very nice story, we think for (oil and gas) generation both off and on our lands, and migration into these large structural features within our lands,” Mery said.
Petrotechnical Resources of Alaska, or PRA, a consultancy firm that has been working for Doyon in its investigations, has in the past suggested that there could be an oil field in the Yukon Flats basin comparable in scale to the Alpine field on the North Slope.
Seeking investors Mery said that Doyon is now actively seeking investors interested in exploration in the two basins, and wants to make contact with companies experienced in the exploration of basins with similar geologic characteristics.
In addition to Yukon Flats’ proximity to the trans-Alaska pipeline, the Nenana basin is adjacent the Alaska Railbelt transportation corridor, the potential site of a pipeline carrying natural gas from the North Slope into Southcentral Alaska. A gas development in the Nenana basin and the development of the gas line could support each other’s economic viability, with Nenana gas potentially increasing the pipeline throughput without infringing statutory limitations on the volumes of North Slope gas that the line could carry, Mery said.
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