Recovery of hydrocarbons from deep underground deposits of tar sands

Claim 1

In a method of mining tar sands which are in beds too deep below the surface to be economically mined by stripping the overburden, and in which a well is sunk through the overburden and the tar sands layer into the underlying bedrock, the well is cemented to the overburden and a hot aqueous fluid is injected into the well and directed against the tar sands to heat the surface of the sands to render the tar therein sufficiently fluid so that it can be slurried into the aqueous fluid, and the slurry is forced up the well to a recovery system on the surface, while maintaining a sufficiently high pressure in the well with a non-condensable gas to support the overburden, the improvement which comprises: (a) Maintaining at least a ten foot thick ceiling of tar sands in the cavity throughout the operations of mining and backfilling in order to provide an gas-impermeable seal and hence preventing the roof from falling in; and (b) Backfilling the cavity after primary hydraulic mining is completed, and before depressurization, with spend sand and aqueous fluid to both ensure against collapse of the cavity after depressurization and to dispose of the sand in an ecologically acceptable manner, whereby energy requirements and surface subsidence are minimized.