Sparsely drilled

Scotian Basin Larger Than Gulf of Mexico

American Association of Petroleum Geologists (AAPG)
Scotian Basin map and data showing the resource potential of the six geographical zones for Play Fairway Analysis of the Scotian Basin.
Scotian Basin map and data showing the resource potential of the six geographical zones for Play Fairway Analysis of the Scotian Basin.

The Scotian Basin lies several hundred kilometers southwest of Newfoundland’s oil producing Grand Banks. Larger than the Gulf of Mexico’s oil and gas producing area, the basin is 200 kilometers wide, 800 kilometers long and 142,000 square kilometers in size. Water depths vary from less than 100 meters to 3,500 meters.

The area contains up to 16,000 meters of sediments.

Sparsely explored to date, the Scotian Margin has been tested by just 204 wells, comprising 127 exploration wells, 28 delineation wells and 49 production wells. Most were drilled between the 1970s-90s, on regional grids of low-fold, 2-D seismic data.

Surprisingly, the area boasts 24 significant discovery licenses, with an average exploration discovery rate of about 25 percent.

The first 3-D seismic surveys were acquired during the early 2000s, but huge areas of the basin have no 3-D seismic data coverage to date.

The study’s data base consisted of 70,000 kilometers of 2-D seismic data, 30,000 square kilometres of 3-D seismic data, and 20 key wells distributed across the basin. Some 7,300 kilometers of 2-D seismic trade data were reprocessed to modern-day standards.

A full biostratigraphic analysis was conducted, and, according to AAPG member Hamish Wilson, “We linked the key wells with what we call ‘bible’ seismic lines, creating for the first time an integrated sequence stratigraphic framework for the basin.”

Ten internally consistent sequence stratigraphic sequences were mapped geophysically across the basin.

Across the basin, investigators delineated the distribution of source rocks juxtaposed with reservoir rocks, and they mapped growth and strike slip fault systems, carbonate banks, deltaic systems, turbidites and authochonous salt.

Window Shopping

Wilson, program director of the PFA study, described how “forensic” geochemistry was used to unlock the story of the Lower Jurassic petroleum system in the southwest part of the Scotian Margin:

Fluid inclusion work in the deepwater Weymouth A-45 well and extensive bio-marker and isotopic analyses of sea floor oil seeps collected in piston cores suggest the syn-rift and early post-rift deposition of a Lower Jurassic source rock that’s currently expelling oil today.

“There’s a regional Lower Jurassic source rock system extending to Morocco,” Wilson said.

Oil generation in the Lower Jurassic occurred before the Deep Panuke reservoirs were sealed. In the eastern part of the Scotian Margin – where Deep Panuke will produce gas from Upper Jurassic Abenaki Formation carbonates – these same Lower Jurassic source rocks are over mature today.

The study suggests, however, that the mostly undrilled carbonate bank, extending southwest along the Scotian Margin, could be filled with oil sourced from Lower Jurassic rocks.

Investigators also analyzed the Scotian Basin’s proven source rocks – currently in the gas window today, these Upper Jurassic rocks sourced the gas in the Sable Sub-basin’s productive Jurassic and Cretaceous deltaic complexes. As the basin shallows toward its margins, these Upper Jurassic source rocks move into the oil window.

Evidence for the concept of an oil rim around the Sable Delta, Wilson said, is provided by the Panuke and Penobscot oil discoveries and shows in this area.

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