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The Hudson Bay basin is a pre-Carboniferous intracratonic basin of about 375,000 sq mi (970,000 sq km) with a maximum sediment thickness of about 8,000 ft (2,400 m). Outcrop study and limited drilling prior to 1970 indicated the presence of Upper Ordovician carbonate rocks with thin, immature source beds; Middle Silurian carbonate rocks, including a significant porous biostromal unit; Upper Silurian to Lower Devonian red beds, evaporites, and carbonate rocks; and Middle to Upper Devonian carbonate rocks, evaporites, and clastics.
Detailed refraction mapping by Aquitaine et al suggested large north-trending fault blocks in the central part of Hudson Bay. Early reflection seismic profiling proved unrewarding until 1973 when Shell Canada Resource employed an experimental energy source and array that largely overcame previous problems. Reflection data confirmed the presence of fault blocks and added previously unavailable stratigraphic and structural detail. After extensive seismic surveys two offshore tests were drilled in 1974. One well (total depth in Precambrian granite at 5,170 ft; 1,550 m) encountered tight, secondarily cemented Silurian carbonate rock; the second test (total depth 4,341 ft; 1,302 m in Precambrian basement) penetrated a thin Carboniferous clastic sequence and found the objective Silurian car onate section salt plugged. No hydrocarbons or indications of source rocks were found in either well. Although three tests in an offshore area about the size of Alberta are not conclusive, the lack of preserved porosity and the absence of hydrocarbons and source rocks are negative indications. However, the presence of up to 8,000 ft (3,400 m) of sediments in the central area of the basin would allow maturation of Ordovician source rocks, if such exist. Thus, there is still some potential in the Hudson _ay basin for hydrocarbon generation and accumulation.
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