Arctic Basin Gets Re-examination

Transformed Canada Arctic Region

Every interpreter has experienced the benefits of "shelving" his seismic interpretation for a couple of weeks — or even a few months — and revisiting it with fresh eyes.

Almost 20 years have passed, however, since most interpreters shelved their seismic interpretations of the Mackenzie Delta and the adjacent Beaufort Sea.

So what's new?

Recent breakthroughs in geological understanding — based upon new geochemistry and biostratigraphy analyses, plus the acquisition of 3-D seismic data — have transformed Canada's Arctic region from a source-limited basin to one that is rich in mature source rock.

Proximity to newly defined source rock beds has opened up a host of new play concepts.

Opening the Window

Situated due east of Alaska's North Slope, the Mackenzie River forms the second largest drainage system in North America. When the Mackenzie River meets the shallow Beaufort Sea, it fans out to form the Mackenzie Delta, an area of 13,500 square kilometers — an area where the distinctions between land and water blur.

Image Caption

Baluga whales in the Beaufort Sea
Graphics courtesy of Devon Canada Corp.

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Every interpreter has experienced the benefits of "shelving" his seismic interpretation for a couple of weeks — or even a few months — and revisiting it with fresh eyes.

Almost 20 years have passed, however, since most interpreters shelved their seismic interpretations of the Mackenzie Delta and the adjacent Beaufort Sea.

So what's new?

Recent breakthroughs in geological understanding — based upon new geochemistry and biostratigraphy analyses, plus the acquisition of 3-D seismic data — have transformed Canada's Arctic region from a source-limited basin to one that is rich in mature source rock.

Proximity to newly defined source rock beds has opened up a host of new play concepts.

Opening the Window

Situated due east of Alaska's North Slope, the Mackenzie River forms the second largest drainage system in North America. When the Mackenzie River meets the shallow Beaufort Sea, it fans out to form the Mackenzie Delta, an area of 13,500 square kilometers — an area where the distinctions between land and water blur.

Underlying this modern delta complex is the Beaufort Mackenzie Basin (BMB), which consists of 12 to 16 kilometers of Tertiary age progradational sediments.

The Geological Survey of Canada (GSC), in conjunction with oil and gas industry partners, has undertaken a reinterpretation of well data in the BMB. Using a multitude of diagnostic tools, the GSC is performing organic geochemistry and petrology studies, including:

  • Vitrinite reflectance.
  • RockEval (Total Organic Carbon).
  • Biostratigraphy.
  • Foraminifera colouration indexes.
  • Apatite fission track analyses.
  • Fluid inclusion homogenization temperatures.

Historically, it was believed that source rock was limited to the Tertiary age Richards Formation, but recent work indicates that three other Tertiary age formations have been expelling hydrocarbons into the basin since mid-Tertiary time: the Aklak, Taglu and Kugmallit formations.

"In order to attract industry, we had to have some proprietary time frame," said AAPG member Dale Issler, a GSC research scientist and project leader of the GSC-industry consortium. "Our project is outcomes driven, and we're strongly aligned to industry's needs."

The selling point for the consortium, Issler said, was a password-protected, Web-accessible database with real-time delivery for the exploration decision-making process. The consortium's work is held for two years before being released in open files.

"In many cases, the oil window is below drill depths in the offshore, so you need to rely on thermal modeling to figure out what's going on," Issler said.

According to Issler, the oil window shallows in the onshore regions of the Mackenzie Delta. The existence of five stacked deltaic complexes in the Tertiary, he said, leads to "extensive recycling of sediments, fossils and organic matter.

"Every tool helps when working in a deltaic environment," he said. "There's very little published in the BMB, in terms of thermal history."

New Potential

A lot of the structures that were drilled in the 1970s and 1980s weren't filled to spill point, explained AAPG member Peter Graham, an exploration geologist with Devon Canada, one of the consortium's industry partners.

"Some people attributed this to a poor source rock basin," he said, describing this problem as a historical "fill to spill" issue.

"The primary risk that we now concern ourselves with is seal integrity," he added.

"The majority of the big structures have been drilled already," said AAPG member Chris Bergquist, also an exploration geologist with Devon Canada. "But the 3-D seismic data have basically opened our eyes to the stratigraphic and structural/stratigraphic plays on the flanks of these structures.

"There's a whole new area of potential that was mostly ignored," Bergquist added, "and the new geochemistry work expands the area of potential for hydrocarbon-charged traps."

Devon has identified several new and exciting Tertiary plays in the offshore: multiple unconformity subcrops and channel fills, turbidites (base-of-slope and basin floor fans) and wrench-related structures.

According to Graham, the biostratigraphy markers described by the GSC can be correlated — and tested — on the new 3-D seismic data. He likened Devon's turbidite play to producing analogs in the Gulf of Mexico and offshore Angola.

"Now we can make out the internal components in the turbidites," Graham said, thanks to he new, high-resolution 3-D seismic data, "and figure out where the reservoirs are."

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