Steam flood oil recovery process

Claim 1

A method for recovering viscous oil from a subterranean, permeable, viscous oil-containing formation, said formation being penetrated by at least two wells, one injection well and one production well, said injection well being in fluid communication with the lower portion of the formation, said production well containing two flow paths from the surface, the first being in fluid communication with at least a portion of the upper part of the formation, and the second being in fluid communication with at least a portion of the lower part of the formation, comprising: (a) injecting steam into only the lower portion of the formation via the injection well and producing fluids including oil from the upper portion of the formation via the first path in the production well until vapor phase steam production occurs at the production well thereby sweeping oil primarily in the upper portion of the formation between the injection well and the production well; and (b) thereafter injecting a thermal recovery fluid comprising steam as hot water into the lower portion of the formation via the second flow path in the production and recovering fluid from the lower portion of the formation via the injection well until the fluid bearing recovered from the injection well comprises an unfavorable amount of steam or water thereby sweeping oil primarily in the lower portion of the formation between the injection well and the production well whereby the vertical conformance of the steam drive is significantly improved and oil recovery is enhanced.

Claim 2

A method for recovering viscous oil from a subterranean, permeable, viscous oil-containing formation, said formation being penetrated by at least two wells, one injection well and one production well, said injection well being in fluid communication with the lower portion of the formation, said production well containing two flow paths from the surface, the first being in fluid communication with at least a portion of the upper part of the formation, and the second being in fluid communication with at least a portion of the lower part of the formation, comprising: (a) injecting steam into only the lower portion of the formation via the injection well and producing fluids including oil from the upper portion of the formation via the first path in the production well until vapor phase steam production occurs at the production well thereby sweeping oil primarily in the upper portion of the formation between the injection well and the production well; and (b) thereafter injecting a thermal recovery fluid comprising steam as hot water into the lower portion of the formation via the second flow path in the production and recovering fluid from the lower portion of the formation via the injection well until the fluid bearing recovered from the injection well comprises an unfavorable amount of steam or water thereby sweeping oil primarily in the lower portion of the formation between the injection well and the production well whereby the vertical conformance of the steam drive is significantly improved and oil recovery is enhanced.