Stair-step thermal recovery of oil

Claim 1

In a process for the recovery of oil from a subsurface oilbearing reservoir which includes at least two productive formations, a first productive formation having three zones - an upper zone predominately saturated with a viscous relatively immobile oil, a lower zone predominately saturated with water, and a saturation transition zone where in oil saturation decreases and water saturation increases with increasing depth and an adjacent second productive formation separated therefrom by a substantially impermeable barrier through which heat may be conducted, the method comprising the steps of: extending at least a first well and a second well to each at least partially traverse said first and second productive formations; determining the location in said first formation of said first zone, second zone and transition zone; opening said first well and said second well into fluid communication with the upper zone, the lower zone, and the transition zone of said first productive formation; preheating at least some of the oil in the upper zone and heating at least some of the oil in said transition zone of said first productive formation by injecting a hot fluid into said first productive interval through said first well whereby said hot fluid moves into said transition zone and said predominately water-saturated lower zone carrying heat into said first productive formation which conductively preheats said upper zone; entraining in hot fluid moving through said transition zone of said first productive formation at least a portion of said preheated oil in the transition zone; producing said entrained oil through said second well along with said fluid; after said preheat step, driving oil to said second well and conductively preheating said adjacent second productive formation by continuously injecting steam simultaneously into the upper, lower, and transition zones of said first productive formation through a single flow path in said first well; and producing fluid from said upper, lower, and transition zones of said first formation through a single flow path in said second well; whereby said steam injected into said transition zone and said lower zone moves toward said second well and rises carrying heat into said first productive formation further heating the oil in said upper zone and entraining at least some heated oil draining from said upper zone into said transition zone and said lower zone, whereby said steam injected into said upper zone further heats the preheated oil in said upper zone and drives said oil in said upper zone to the second well, and whereby the adjacent second productive formation is preheated by heat conducted from said first productive formation through said impermeable barrier; opening said first well and said second well into fluid communication with said adjacent second productive formation; providing a separate confined path for fluid flow into said adjacent second productive formation through said first well; driving oil from said adjacent second productive formation by injecting a heated fluid into said second productive formation through said separate confined path for fluid flow in said first well while continuing to inject steam into said first productive formation; producing oil from said second productive formation through said second well; determining when steam breakthrough into said second well from said first productive formation occurs; and when said steam breakthrough occurs, plugging back at least some of that portion of said second well open into fluid communication with said first productive formation to shut off at least some of said steam breakthrough.