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Petroleum System Characteristics of Cretaceous-Paleogene Strata, Bylot Island, Nunavut

James W. Haggart1, Hans Wielens2 (deceased), Lisel Currie3, Kirk Osadetz3, Gordon N. Oakey2, and Elliott T. Burden4
1Geological Survey of Canada, Vancouver, BC, Canada.
2Geological Survey of Canada, Dartmouth, NS, Canada.
3Geological Survey of Canada, Calgary, AB, Canada.
4Earth Sciences, Memorial University Newfoundland, St John's, NF, Canada.

Cretaceous-Paleogene (K-P) strata found on Bylot Island, Nunavut, aggregate more than 1 km in total thickness and include alternating sandstone and mudstone units with local coals at the base of the succession. The strata reflect deposition in a variety of subaerial to submarine-fan environments. The Bylot Island rocks are related to oil-and-gas-bearing K-P strata of West Greenland and all K-P strata of the circum-Baffin Bay region are inferred to have accumulated in rift-related tectonic basins.

The Bylot Island strata are being studied to assess their potential petroleum system elements, specifically as source and reservoir rock, and as a proxy for the adjacent offshore successions of Lancaster Sound and the continental shelf off northern Baffin Island. Sub-bituminous coals in the succession provide reliable indications that organic maturity did not exceed vitrinite reflectance equivalents of 0.5% and that strata reached maximum paleotemperatures not exceeding ~60-80 degrees C as a result of maximum burial depths between 1.4-2.5 km (using a geothermal gradient inferred by others from reflection seismic data indicating the Type I gas hydrate stability zone base in Lancaster Sound). Preliminary Rock Eval results show a high proportion of samples (∼ 40%) with reasonable to good, predominantly gas-prone (Type II-III OM) source-rock potential, based on TOC and HI. Tmax values range between 410-440 degrees C. Available coal-rank data suggest that Tmax values exceeding 429 are anomalously high and not reflective of the organic maturity of the succession, probably due to either sedimentary recycling or diagenetic oxidation. Sandstone packages are locally >10 m in thickness and typically stacked in multiples. Most sands are poorly consolidated and friable with a minimum of cement; many are well-sorted and mature with minimal to no visible clay. The abundance of friable sandstone across Bylot Island suggests the general possibility of good porosity and permeability regionally; 8 samples of consolidated sandstone analyzed quantitatively exhibit porosity values ranging up to >30% and permeability values locally greater than 1000 mD, suggesting good to excellent reservoir potential locally. Consolidated and unconsolidated sandstone samples analyzed with XRD were found to consist of 95-100% quartz, with accessory feldspar and minor carbonate which could degrade reservoir potential.
Mudstone intervals within the Bylot Island K-P succession provide numerous possibilities as reservoir seals. Lithostratigraphic correlation suggests that some sandstone packages on Bylot Island grade laterally into adjacent mudstone and provide opportunity for stratigraphic traps. Elsewhere, high-angle structures cutting K-P strata of Bylot Island are noted, juxtaposing sandstone and shale units and providing opportunity for structural traps. Structural trends noted onshore are interpreted to continue into the adjacent offshore region.

 

AAPG Search and Discovery Article #90130©2011 3P Arctic, The Polar Petroleum Potential Conference & Exhibition, Halifax, Nova Scotia, Canada, 30 August-2 September, 2011.

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