Rotary drilling and extracting process

A process for in situ extraction of bitumen values from subterranean tar sand deposits, which comprises:

• drilling a pilot hole of relatively narrow diameter from the ground surface, through the overburden and the tar sand deposit and a distance of 2-21/2 times the thickness of the tar sand deposit into the sub-tar sand formation located beneath the tar sand deposit;
• enlarging the pilot hole below the tar sand formation to form a sub-tar sand cavern and extracting the mined materials from said sub-tar sand tar cavern to the ground surface through said pilot hole;
• filling the sub-tar sand cavern with aqueous liquid;
• enlarging the pilot hole radially in the tar sand deposit by treating the tar sand deposit with circulating high pressure jets of heated mining fluid comprising a mixture of water and normally gaseous hydrocarbons, the temperature difference between the in situ deposit and the mining fluid immediately prior to issue from the jets being at least 60.degree. F., to cause breakup of the tar sand deposit and interaction of the bitumen portion of said deposit with gases of the mining fluid, and to form a tar sand cavern;
• agitating the liquid slurry of tar sand and mining fluid formed in the tar sand cavern to wash and cause downward settling of the sand component of the tar sand;
• and upwardly displacing the separated oil component to the ground surface.