At Saddle Lake, Alberta, in the Lower Cretaceous Colony Formation, lenticular sandstones 25 m thick contain 13.7 degree API heavy viscous oil at a depth of about 500 metres. The lenticular sandstones, from their electric log character, are interpreted to be point bars deposited by lateral accretion within a highly meandering large river system.
Each hydrocarbon-bearing lenticular sandstone contains a gas cap with an underlying heavy oil column, which in turn is underlain by salt water. The thickest oil columns are 9.8 to 14.0 metres thick and the gas caps have been largely depleted. Entrapment of the gas and oil appears to be caused by the overlying Joli Fou shale which forms a roof-seal and by shale-filled entrenched meandering river channels or oxbows which surround the hydrocarbon bearing sandstones.
In the present scheme, recovery of the heavy oil by in situ combustion is proposed in two stages as follows:
burn-out of the gas remaining in the gas cap, and
combustion of the oil from the top of the oil column downward by injection of oxygen (or air) through vertical wells arranged in a line drive pattern, with recovery of oil through horizontal wells drilled within but near the base of the oil column.