The Wabasca oil sands deposit in north-central Alberta contains 24 billion bbl of bitumen in the Grand Rapids Formation (Albian, Lower Cretaceous). The 6 to 8° API bitumen has a viscosity at reservoir temperature (65°F) of 2 million cp. and a sulphur content of 4.6 wt. %. Since 1974 Gulf Canada has been experimenting with in-situ fireflood, cyclic-steam stimulation, steam flood and solvent processes in the uppermost "A" Member of the formation.

A gentle southwestward-dipping homocline in this area is locally complicated by differential compaction of Lower Cretaceous sediments over paleotopographic relief on the Paleozoic erosion surface. In the pilot area, low amplitude (10 ft), northwest oriented folds may represent compactional features or wrinkles produced by the down-dip creep and buckling of the unconsolidated sand.

The Grand Rapids "A" reservoir is entirely sand, 45 to 50 ft thick, and divisible into three members on the basis of grain size and sedimentary structures. Grain size increases upwards from very fine at the base of the Lower Member to fine sand in the Middle Member. In the Upper Member, grain size decreases upwards from granuliferous, coarse sand at the erosional base to fine

End_Page 960------------------------------

sand at the top.

Oil saturation varies from 0 to 14 wt. % (average 8.5 wt. %), and is zero within: (1) calcite cemented beds, (2) a basal water zone varying from 4.5 to 11.5 ft thick, and (3) a thin water zone at the top of the reservoir.

Log porosity of saturated sand ranges up to 36%; permeability reaches 25 md and several darcys after extraction. The reservoir contains seven thin (0.5 to 1.5 ft), tightly calcite cemented beds that form permeability barriers. Permeability is highly directional and correlative with grain fabric. Oil saturation is controlled by grain size, fines, sorting, roundness and authigenic clay.

Current pilot experiments have been inconclusive. Difficulties have occurred with injection into oil-saturated sand and confinement therein. Laboratory simulation experiments have resulted in marked chemical and physical reservoir changes.

End_of_Article - Last_Page 961------------