Upper Ordovician reefs in the Hudson Bay Basin ...

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context of hydrocarbon systems in the Hudson Bay. Basin. 2. The reefs are directly on top of TOC-rich, Type I-IIs oil- prone source rock. 3. The reefs are locally ...

Upper Ordovician reefs in the Hudson Bay Basin: Porosity evolution and hydrocarbon charge Denis Lavoie1, Ariane Castagner2, Omid Haeri Ardakani1 and André Desrochers2 1- Geological Survey of Canada 2- Ottawa University

Outline  The Hudson Bay Basin – geological setting and hydrocarbon exploration history  Source rocks  Potential reservoirs  Upper Ordovician reef of the Red Head Rapids Formation  Diagenetic evolution – petrography-geochemistry-fluid inclusions

 Evidence for hydrocarbon migration  On-going research and conclusions

The largest intracratonic basin in North America

Regional setting and historic background

46 000 linear-km of industry seismic (1970’s) 40 000 linear-km of GSC seismic (1980-1990) 5 wells in the Bay 1 well Akpatok Island 3 wells Manitoba 1 well northern Ontario

Devonian to Upper Ordovician shallow marine platform carbonates, shales and local bioherms ------------------------------variably thick, restricted marine evaporites ------------------------------thin, widespread organic-rich shales -------------------------------thin sections of coastal plain sandstones

Lithostratigraphy U3

U2 U1 Dietrich et al (2012, SEG)

Basin geometry

New seismic interpretation 3 major unconformities Ordovician-Silurian: U1 Upper Silurian-Lower Devonian: U2 Middle Devonian: U3

Source rocks 1- Yields: 20 - 134 kg/tonne

Reef locality



TOC: 5 - 35% - 5 meters 3

2- Yields: 16 - 99 kg/tonne TOC: 3 - 15% - 15 meters

3- Yields: 2 – 11 kg/tonne TOC: 4 - 5% - 12 meters 4- Yields: 13 – 74 kg/tonne TOC: 3 – 15% - 10 meters


Research highlights 1. Evaluate the reservoir potential of the reef facies in the Upper Ordovican Red Head Rapids Formation in the context of hydrocarbon systems in the Hudson Bay Basin 2. The reefs are directly on top of TOC-rich, Type I-IIs oilprone source rock 3. The reefs are locally highly porous with report of dead oil and bitumen in pore space

Massive reef – Southampton Island

180 m

500 m


Interpreted sub-surface presence

Top Silurian Top Ordovician

Pore and fracture-filling bitumen Very porous

Ordovician – Silurian unconformity

Facies Two main facies: Cementstones



5 mm

Laminated automicrite

5 mm

Paragenetic succession

Cement succession – marine isopachous

Cement succession – marine botryoids

Cement succession – dissolution

Cement succession – late (post dissolution) cements

Cement succession - bitumen

Cement succession - bitumen

Geochemistry – Stable isotopes

Fluid inclusions – work in progress

Late fluid composition

Hydrocarbon generation and migration ? Abundant, potential oil slicks in the area as determined through RADARSAT images

Upcoming research – the hunt for pockmarks Seabed mapping in strategic areas in Foxe Channel and Hudson Strait

Upcoming research – refining thermal history Rock Eval (black shales): Tmax: 421 - 432˚C (Lavoie et al., 2013, OF 7363) immature Apatite Fission Track (basal sandstone): 65 - 85°C (Pinet et al., 2016, OF 8110) early mature Fluid inclusions (late cements, in progress): 75 - 150°C oil window Clumped isotopes (late cements): in progress

Conclusions 1. The Upper Ordovician reef in the RHR Formation mainly displays boundstone and cementstone microfacies with abundant synsedimentary (aragonite – now calcite) and post-dissolution (calcite) cements. 2. Bitumen is present in fracture and dissolution pore spaces 3. Late cement phases are depleted in both δ18O and δ13C 4. Fluid inclusions are mostly saline (>12%) and high temperature (2 groups; one average of 115°C another at 80°C) 5. Possible local circulation of fault/fracture controlled hydrothermal fluids – no pervasive alteration noted


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