Alternating sagd injections

Abstract

Methods produce heavy oil with steam assisted gravity drainage. Such methods alternate a traditional steam injection with an injection of a steam-plus-non-condensable gas (such as CO 2 or CO 2 -plus-diluent) mixture. The CO 2 /diluent mixture is soluble in bitumen, leading to a reduction in viscosity of the heavy oil. Additionally, the steam-only injection reduces the accumulation of vapor NCG along the edge of the steam chamber, leading to improved thermal efficiency.

What is claimed is: 
     
         1 . A method of enhancing recovery of hydrocarbons from a heavy oil reservoir, comprising:
 a) providing an injection well that intersects the heavy oil reservoir;   b) providing a production well that intersects the heavy oil reservoir, wherein the injection well is in fluid communication with the production well;   c) co-injecting steam and a non-hydrocarbon non-condensable gas (NCG) into the injection well for a first time;   d) injecting steam without the NCG into the injection well for a second time subsequent to the first time;   e) producing hydrocarbons from the production well; and   f) repeating steps c and d.   
     
     
         2 . The method of  claim 1 , wherein the injection and production wells are paired to allow a gravity drainage process, the co-injecting uses a mixture of the steam with 10-12 percent by weight of the NCG produced in a direct-steam-generator, and the injecting of the steam uses output from a steam generator having exhausted flue gas. 
     
     
         3 . The method of  claim 1 , wherein said NCG comprises CO 2 . 
     
     
         4 . The method of  claim 1 , wherein said NCG comprises CO 2  and is further co-injected with a diluent. 
     
     
         5 . The method of  claim 1 , wherein the steam and NCG is further co-injected with a diluent, and wherein said NCG contains at least one of CO 2 , CO, He, H 2  and N 2 , and said diluent is chosen from hydrocarbon solvents having 1 to 30 carbons. 
     
     
         6 . The method of  claim 1 , wherein said injection well and said production well are horizontal parallel wells and said injection well is disposed 3-10 meters above said production well. 
     
     
         7 . The method of  claim 1 , wherein said NCG is chosen from a group consisting of CO 2 , CO, N 2 , H 2 , He, air, and flue gas. 
     
     
         8 . The method of  claim 1 , wherein the steam and NCG is further co-injected with a diluent that is 85% C5+ hydrocarbons. 
     
     
         9 . The method of  claim 1 , wherein said NCG comprises CO 2  and is further co-injected with a diluent that includes C1-C8 hydrocarbons. 
     
     
         10 . The method of  claim 1 , wherein the injecting of the steam in step d without introducing additional non-condensable constituents along with the producing in step e depletes accumulation of the NCG in the reservoir. 
     
     
         11 . The method of  claim 1 , wherein a ratio of first time/second time is between 1:1 and 3:1. 
     
     
         12 . The method of  claim 1 , wherein a ratio of first time/second time is 2:1. 
     
     
         13 . An improved method for steam recovery of heavy oil from a formation, the method involving mobilizing heavy oil with steam-plus-non-condensable-gas (NCG), and recovering said mobilized heavy oil, the improvement comprising alternating an injection of steam lacking the NCG with co-injection of steam-plus-NCG and recovering mobilized heavy oil, wherein the NCG is a non-hydrocarbon and a cumulative steam-to-oil ratio is reduced as compared with steam-plus-NCG co-injection alone or a rate of heavy oil production is higher as compared with steam-plus-NCG co-injection alone. 
     
     
         14 . The method of  claim 13 , wherein said method for steam recovery of heavy oil is steam assisted gravity drainage (SAGD), Expanding Solvent SAGD, Vapor Extraction (VAPEX), Steam And Gas Push (SAGP); cyclic steam stimulation (CCS), and combinations and variations thereof. 
     
     
         15 . The method of  claim 13 , wherein said NCG comprises CO 2 . 
     
     
         16 . The method of  claim 13 , wherein said NCG comprises CO 2  and is further co-injected with a diluent. 
     
     
         17 . The method of  claim 13 , wherein the steam and NCG is further co-injected with a diluent, and wherein said NCG contains at least one of CO 2 , CO, He, H 2  and N 2 , and said diluent is chosen from hydrocarbon solvents having 1 to 30 carbons. 
     
     
         18 . The method of  claim 13 , wherein said NCG is chosen from a group consisting of CO 2 , CO, N 2 , H 2 , He, air, and flue gas. 
     
     
         19 . The method of  claim 13 , wherein the steam and NCG is further co-injected with a diluent that is 85% C5+ hydrocarbons. 
     
     
         20 . The method of  claim 13 , wherein said NCG comprises CO 2  and is further co-injected with a diluent that includes C1-C8 hydrocarbons.