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The Western Canada sedimentary basin contains tar deposits in Lower Cretaceous sands and on the Paleozoic unconformity surface which exceed by 3 times the known recoverable oil reserves of the entire world. The tar was originally liquid oil which has been degraded by aerobic bacteria.
The Athabasca anticline, a drape structure caused by Devonian salt removal, connects southward with the Sweetgrass arch to form a 600-mi long structural barrier on the eastern, updip rim of the basin. Most of the tar deposits are along the anticline or in a giant stratigraphic trap on the west flank of the anticline. There is no oil or gas east of the anticline.
In the deepest part of the basin the Mesozoic section generated gas in enormous volumes. Most of the gas has escaped to the outcrop, a small amount is contained in thousands of conventional stratigraphic pools on the east side, and a very large volume is contained in tight sands on the west side, or in the Deep basin. Most of the reservoirs are Lower Cretaceous sands. The tight, gas saturated sands grade updip into porous water saturated sands. The trap is not tightly sealed but leaks off at a steady rate. Continuing gas generation keeps the trap pumped full. This bottleneck trap contains 1,700 tcf of gas in place.
The gigantic oil and gas accumulations of the Lower Cretaceous make the Western Canada sedimentary basin the richest hydrocarbon province in the world.
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