Automated subcool control

Abstract

The present disclosure relates to a method and system for automated subcool control, wherein the controller is a traditional proportional integral controller based on gap control low select logic and the output controls pump speed for the artificial lift pump.

1 . A method of automated subcool control in a steam-assisted gravity drive oil well, comprising:
 a) providing a producer well having one or more temperature sensors therein for measuring a temperature of a production fluid (Tb) and one or more pressure sensors for measuring pressure at bottomhole conditions (Pb), and one or more pressure sensors for measuring pressure at a casing head (Pc);   b) providing a pump motor fluidly connected to said producer well for pumping a production fluid to the surface;   c) calculating a submergence pressure Sp=Pb−Pc;   d) calculating a steam saturation temperature (Ts) at Pb and Tb using an equation that approximates steam tables;   e) providing a primary proportional integral (PI) controller for controlling subcool temperature (TIC) based on a gap control algorithm;   f) providing a secondary proportional integral (PI) controller for controlling a current of said motor (IIC) when said pump motor's current approaches a high alarm set point;   g) providing a secondary proportional integral (PI) controller for controlling a submergence pressure (PDIC) when said submergence pressure approaches a low alarm set point;   h) wherein each said PI controller uses a low select algorithm to contribute a lowest value for adjusting a speed of said motor so as to approach a target subcool temperature (TΔ=Ts−Tb), maintain acceptable motor current, or acceptable submergence pressure.   
     
     
         2 . The method of  claim 1 , said pump motor further including a temperature sensor that measures the temperature of said pump motor, and further including an override function whereby said pump motor's speed cannot be increased when said pump motor's temperature reaches an alarm point. 
     
     
         3 . The method of  claim 1 , wherein said target subcool (TΔ) temperature is between 5-15° C./m with a gap allowance of ±1-5° C. 
     
     
         4 . The method of  claim 1 , wherein said target subcool (TΔ) temperature is 7-12° C./m with a gap allowance of 1-3° C. 
     
     
         5 . An improved method of subcool control in steam assisted gravity drive oil production, wherein steam is injected into a top horizontal well to mobilize heavy oil which gravity drains to a bottom production well and is then pumped to the surface using a pump and where a subcool is desirably kept at a target subcool, the improvement comprising automatically keeping a subcool at target subcool using a PI controller having an output that controls pump speed using a low select algorithm based primarily on gap control of subcool temperature. 
     
     
         6 . The method of  claim 5 , wherein a secondary PI control system intervenes with a low select algorithm when ii) a high alarm set point for motor current is reached or iii) a low alarm set point for submergence pressure is reached. 
     
     
         7 . The method of  claim 5 , further including an override function whereby said pump motor's speed cannot be increased when a temperature of said pump motor reaches a high alarm point. 
     
     
         8 . The method of  claim 5 , wherein said target subcool is 5-15° C./m and said gap is +/−1-5° C. 
     
     
         9 . An method of subcool control in steam assisted oil production, wherein a subcool is desirably kept at a target subcool using a PI controller having an output that controls pump speed using a primary low select and gap control algorithm based on subcool temperature, and secondary PI controller(s) intervene with a low select algorithm when ii) a high alarm set point for pump speed is approached or iii) a low alarm set point for submergence pressure is approached. 
     
     
         10 . The method of  claim 9 , further including an override function whereby said pump speed cannot be increased when a temperature of said pump speed reaches a high alarm point. 
     
     
         11 . A system for automated subcool control of a steam assisted oil recovery; said system including a gap control PI controller that adjusts a pump speed to maintain a target subcool, and includes a PI controller for low select intervention when said pump current approaches a high alarm value and includes a PI controller for a low select intervention when a submergence pressure approaches a low alarm value. 
     
     
         12 . The system of  claim 11 , said system further including a producer well having one or more temperature sensors therein for measuring a temperature of a production fluid (Tb) and one or more pressure sensors at bottomhole conditions (Pb) and one or more pressure sensors at a casing head (Pc). 
     
     
         13 . The system of  claim 12 , said system further including a temperature sensor on said motor and an override function whereby motor speed cannot be increased when a temperature of said motor reaches a high alarm point.