Method of recovering viscous petroleum from thick tar sand

Recovery of viscous petroleum such as from thick tar sands is assisted using a closed-loop flow path formed in a well by concentric casing and tubular members extending from the earth's surface through a substantial portion of the formation for conducting hot fluid to reduce the viscosity of the petroleum in the formation to develop a potential passage in the formation outside the flow path into which a drive fluid is injected to promote movement of the petroleum to the well for production up a production flow line extending up the interior of the tubular member.