AAPG Europe Regional Conference, Global Analogues of the Atlantic Margin

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Potential Cretaceous source-rocks from the north-east Baffin Bay, West Greenland.

Abstract

Eleven, fully cored boreholes, with depths up to ~360 meter were drilled in 2012 in the north-east Baffin Bay, offshore West Greenland. The cores have been investigated with the aim to achieve a better understanding of the petroleum system associated with Mesozoic to Early Tertiary rift basins in this frontier area. The sites were cored by JOIDES Resolution during the Baffin Bay scientific shallow coring program, expedition 344S, August to October 2012, funded by a consortium of eight petroleum companies: Shell, GDF Suez, ConocoPhillips, Statoil, Nunaoil, Dong, Maersk Oil, and Cairn Energy. Notably until 2012, no wells had been drilled in the north-east Baffin Bay. The main drilling target was a succession of dipping strata in the Kap York Basin, that turned out to be of Cretaceous age. Two complementary sites were cored further south on the western fringe of the Melville Bay. A multi-disciplinary work program was carried out at the Geological Survey of Denmark and Greenland (GEUS) for the consortium led by Shell. The new results involved sedimentological core description, palynological dating, palynofacies studies, isotope geochronology and organic-geochemistry of the mudstone successions and reservoir characterization of the sandstone intervals, as well as a seismic-stratigraphic study. The Lower Cretaceous sedimentary succession rests unconformably on Proterozoic strata at three sites. The succession is heterolithic in character, including sandstones, mudstones and thin coal beds. Potential reservoir quality was indicated by an accumulated sandstone thickness of ~100 m with an estimated porosity of 25%. The organic sedimentary particles are dominated by terrestrial material together with a low diverse and rare dinoflagellate cysts (dinocysts) assemblage of brackish-water species, suggesting an aquatic, but non-marine depositional setting. Inferred sedimentary environments include floodplain, swamp, lake, prodelta, bay-margin shoreface and deep bay, which, in combination with palynological results and seismic configuration, suggest accumulation in a large non-marine to brackish embayment formed during an initial rifting stage. The kerogen type in the Lower Cretaceous succession is described as immature to marginally mature type III/IV, either with very restricted potential for generation and expulsion of petroleum or minor potential for generation and expulsion of predominantly gaseous petroleum. However, a few samples may show potential for oil generation. The Upper Cretaceous sedimentary succession consists of black marine mudstone with varying amounts of discrete sand layers. The amorphous organic material and marine dinocysts suggest that the major part of the Upper Cretaceous succession was deposited in an oxygen restricted palaeoenvironment, most probably ranging from anoxic-dysoxic outer shelf and pro-delta fringe to oxygen-restricted lower delta front. The organic richness and petroleum potential of the Upper Cretaceous succession is variable. The black mudstones include intervals with TOC of 3-6% and HI of 200-350. A combined interval of 335 meter thermally immature gas/oil-prone source rock has been defined with a calculated Source Potential Index (SPI) of 4.5, comparable to several petroliferous basins worldwide. Despite the overall marine setting, the basin was influenced by abundant sediment input from terrestrial sources.