Enhanced recovery method and apparatus

Abstract

A water-alternating gas (WAG) apparatus and associated method of operation, the apparatus being located or locatable in a wellbore that extends from a surface to a subsurface location, the apparatus comprising at least one first channel configured to convey a liquid downhole from the surface; at least one second channel configured to convey a gas downhole from the surface; and wherein the apparatus comprises one or more downhole valve systems for switching the downhole apparatus between alternatingly providing the liquid at the downhole location and gas at the downhole location.

1 . A water-alternating gas (WAG) apparatus located or locatable in a wellbore that extends from a surface to a subsurface location, the apparatus comprising:
 at least one first channel configured to convey a liquid downhole from the surface;   at least one second channel configured to convey a gas downhole from the surface; and   one or more downhole valve systems for switching the downhole apparatus between alternatingly providing the liquid downhole and the gas downhole.   
     
     
         2 . The WAG apparatus of  claim 1 , wherein the one or more downhole valve systems are adapted to selectively provide the liquid or the gas downhole from the respective first and second channels. 
     
     
         3 . The WAG apparatus of  claim 1  wherein the one or more downhole valve systems comprise one or more first valves or devices for regulating flow of the liquid downhole and/or one or more second valves or devices for regulating flow of the gas downhole; wherein
 the downhole apparatus is switchable between a first configuration in which the first valves or devices are closed and the second valves or devices are open such that gas is injected or injectable downhole via the at least one second channel and the at least one second valves or devices and a second configuration in which the first valves or devices are open and the second valves or devices are closed such that the liquid is injected or injectable downhole via the at least one first channel and the at least one first valves or devices. 
 
     
     
         4 . The WAG apparatus according to  claim 1 , comprising:
 a tubular or other hollow conduit defining or comprising the first channel; and   one or more hollow casings each defining a passage; wherein   the tubular or other conduit is located or comprised within the passage of the one or more casings and the second channel is comprised in or at least partially defined by one or more annuli provided or at least partially defined between the tubular or other conduit and an inner wall of one of the casings and/or between two casings.   
     
     
         5 . The WAG apparatus according to  claim 3 , wherein the at least one second valve comprises a gas injection device for providing selective communication from the second channel to the first channel 
     
     
         6 . The WAG apparatus according to  claim 3 , wherein the at least one second valve is provided or providable downhole, downstream and/or lower than the at least one first valve. 
     
     
         7 . The WAG apparatus according to  claim 3 , wherein the at least one first valve comprises a sub-surface safety valve configured to selectively open close the first channel 
     
     
         8 . The WAG apparatus according to  claim 3 , wherein the apparatus is adapted to retain a head of liquid in the first channel uphole or upstream of the at least one first valve when the first valve is closed during an injection operation. 
     
     
         9 . The WAG apparatus according to  claim 3 , wherein:
 the apparatus comprises or is connectable to a liquid injection system, the liquid injection system being connected or connectable to the first channel via a liquid control valve and/or   the apparatus comprises or is connectable to a gas injection system, the gas injection system being connected or connectable to the second channel via a gas control valve.   
     
     
         10 . The WAG apparatus according to  claim 9 , wherein the apparatus is switchable between configurations in which the gas and liquid are alternately injected, wherein
 the apparatus is switchable into a liquid injection configuration by opening the liquid control valve and/or the first valve and closing the gas control valve and/or the second valve; and/or   the apparatus is switchable into a gas injection configuration by opening the gas control valve and/or the second valve and closing the liquid control valve and/or the first valve.   
     
     
         11 . The WAG apparatus according to  claim 1 , wherein the apparatus is configured to provide gas at flow rates between 5 and 30 MMscf/d (between 5,900 Nm 3 ·hr −1  and 35,400 Nm 3 ·hr −1 . 
     
     
         12 . A method for performing a water-alternating-gas injection operation in a wellbore that extends from a surface, the method comprising:
 conveying a liquid downhole from the surface in a first channel;   conveying a gas downhole from the surface in a second channel; and   operating one or more downhole valve systems so as to switch the downhole apparatus between alternately providing the liquid downhole and the gas downhole.   
     
     
         13 . The method of  claim 12 , comprising operating the one or more downhole valve systems to selectively provide the liquid or the gas to a downhole location from the respective first and second channels. 
     
     
         14 . (canceled) 
     
     
         15 . The method of  claim 12 , wherein the method comprises performing a downhole gas injection to liquid injection switchover. 
     
     
         16 . The method of  claim 15 , wherein the gas injection to liquid injection switchover comprises:
 closing a downhole gas control valve for controlling gas supplied by a gas injection system and/or using a second valve for regulating flow of the gas downhole; and   opening a downhole liquid a control valve for controlling liquid supplied by a liquid injection system and/or using a first valve for regulating flow of the liquid downhole.   
     
     
         17 . The method of  claim 16 , wherein the method comprises retaining a head of liquid upstream by the first valve and the gas injection to liquid injection switchover comprises releasing the head of liquid by opening the first valve. 
     
     
         18 . The method according to  claim 17 , wherein the method comprises performing a liquid injection to gas injection switchover. 
     
     
         19 . The method according to  claim 18 , wherein the liquid injection to gas injection switchover comprises:
 closing the liquid control valve and/or the first valve; and   opening the gas control valve and/or the second valve.   
     
     
         20 . The method according to  claim 19 , wherein the liquid injection to gas injection switchover comprises ramping up or gradually increasing pressure of gas by gradually opening the gas control valve. 
     
     
         21 . The method according to  claim 12 , wherein the method comprises providing gas at flow rates between 8 and 30 MMscf/d.