Throttling boiler for fouling mitigation

Abstract

Methods and systems generate steam for thermal oil recovery, such as a steam assisted gravity drainage (SAGD) operation. Feedwater is first pressurized to a pressure above that desired for steam injection in the SAGD operation before being heated to avoid at least some nucleate boiling. After being throttled, the local boiling regime is beyond the nucleate boiling regime due to the local pressure drop and the enhanced mixing caused by the throttling process. Two-phase liquid may continue through the boiler generating higher quality steam.

What is claimed is: 
     
         1 . A method of producing steam for oil production, comprising:
 a) providing feedwater through a steam generator system under sufficient pressure to heat said feedwater and prevent formation of steam in an output of heated feedwater;   b) passing said heated feedwater to a pressure reducer where said heated feedwater is flashed to steam; and   c) conveying said steam into a wellbore for mobilizing oil.   
     
     
         2 . The method of  claim 1 , wherein the steam generator is a once-through steam generator. 
     
     
         3 . The method of  claim 1 , wherein the feedwater in step a) is pressurized to at least 14,000 kilopascals. 
     
     
         4 . The method of  claim 1 , wherein the feedwater in step a) is pressurized to at least 20,000 kilopascals. 
     
     
         5 . The method of  claim 1 , wherein the pressure reduction in step b) decreases pressure by at least 3500 kilopascals. 
     
     
         6 . The method of  claim 1 , wherein the pressure reduction in step b) decreases pressure by at least 6500 kilopascals. 
     
     
         7 . The method of  claim 1 , wherein said feedwater in step b) is pressurized by a pump. 
     
     
         8 . A steam generator system for oil production, comprising:
 a) an economizer for preheating feedwater;   b) a radiant section for heating said feedwater from said economizer;   c) a pressurizing element for increasing the pressure of said system enough to prevent nucleate boiling of the feedwater at least within the economizer;   d) a pressure-reducing element for reducing the pressure and producing flash steam; and   e) an injection assembly for injecting the flash steam into an oil reservoir,   wherein elements a though e are fluidly connected.   
     
     
         9 . The steam generator system of  claim 8 , further comprising a flash vessel. 
     
     
         10 . The steam generator system of  claim 8 , wherein said pressure-reducing element is at least one of an orifice and a throttling valve. 
     
     
         11 . The steam generator system of  claim 8 , wherein said pressure-reducing element reduces the system pressure of said feedwater from said radiant section. 
     
     
         12 . The steam generator system of  claim 8 , wherein said pressure-reducing element reduces the system pressure from said economizer. 
     
     
         13 . The steam generator system of  claim 8 , wherein said steam generator system is a once-through steam generator. 
     
     
         14 . The steam generator system of  claim 8 , wherein said pressurizing element is a pump. 
     
     
         15 . The steam generator system of  claim 8 , wherein said pressurizing element increases the pressure of said feedwater to at least 14,000 kilopascals. 
     
     
         16 . The steam generator system of  claim 8 , wherein said pressurizing element increases the pressure of said feedwater to at least 20,000 kilopascals. 
     
     
         17 . The steam generator system of  claim 8 , wherein said pressure-reducing element reduces the pressure by at least 3500 kilopascals. 
     
     
         18 . The steam generator system of  claim 8 , wherein said pressure-reducing element reduces the pressure by at least 6500 kilopascals. 
     
     
         19 . An improved method of producing oil, the method comprising generating steam to inject into a wellbore and mobilize oil for production, the improvement comprising heating feedwater under a pressure sufficient to prevent nucleate boiling, reducing said pressure to make flash steam prior to any nucleate boiling of the feedwater and injecting said flash steam into a wellbore to mobilize the oil for production.