Method for recovering viscous petroleum from unconsolidated mineral

Abstract

Disclosed is a method whereby viscous petroleum may be recovered from a subterranean viscous petroleum-containing formation in which the formation mineral matrix is substantially unconsolidated, such as a tar sand deposit. A hot fluid such as steam is injected into the formation and pressure maintained thereon for a period of time to heat the viscous petroleum in the immediate vicinity of the well bore, which causes the unconsolidated mineral grains to settle to the bottom of the formation with the viscous oil located on the top of the settled grains. The injection pressure maintenance phase is then terminated and petroleum is recovered from the upper portion of the formation. Numerous cycles of hot fluid injection, soak, followed by production of petroleum from the upper portion of the cavity are required to exploit a reasonable aerial extent of the formation by this method. The separation is enhanced by introducing a solvent material for the viscous petroleum which has a specific gravity substantially less than the specific gravity of petroleums, such as a low molecular weight hydrocarbon solvent, or introducing a fluid which is immiscible with petroleum and which has specific gravity substantially greater than the specific gravity of the viscous petroleum, such as a dense brine which settles to the bottom portion of the cavity and displaces petroleum upward. Both treatments may be employed simultaneously for optimum recovery.