Method and system for stepwisevarying fluid flow in well

Abstract

A method for stepwise varying fluid flow in a well utilizes a plurality of downhole valves which have orifices of different sizes in the valve bodies, so that fluid flow can be varied by partially closing one or more valves. The method may be used for testing gas wells such that the wellbore storage delays caused by gas compression and/or expansion in the production tubing are minimized.

1 . A method for stepwise varying fluid flow in a well by means of a downhole valve assembly that can be switched between a first position in which fluid flow is permitted and a second position in which fluid flow is inhibited, wherein the valve assembly comprises a plurality of valves which each comprise an orifice through which a limited flow of fluid is allowed when the valve is in the second position thereof.  
     
     
         2 . The method of  claim 1 , wherein the valves comprise orifices that form different flow restrictions and wherein the method is used to determine the properties of the rate-dependent skin around the inflow region of a gas production well and wherein during a selected period of time a first valve is in the second position and each of the valves are in the first position thereof, which period is followed by another selected period of time during which a second valve is in the second position and each of the other valves is in the first position thereof.  
     
     
         3 . The method of  claim 2 , wherein the valve assembly comprises at least three valves and wherein during a first period of time a first valve, which has an orifice that forms a larger flow restriction than the other valves is maintained in the second position and the other valves are in the first position thereof, which period of time is followed by a second period during which a second valve which has an orifice that forms a smaller flow restriction than the first valve, but larger flow restriction than the other valve or valves, is in the second position and the other valves are in the first position and which second period of time is followed by a third period of time during which a third valve which has an orifice that forms a smaller flow restriction than the orifices of the first and second valves is in the second position and the first and second valves are in the first position.  
     
     
         4 . The method of  claim 3 , wherein said first, second and third periods of time have a substantially equal duration which is between 0.5 and 50 hours.  
     
     
         5 . The method of  claim 4 , wherein said duration is between 1 and 20 hours.  
     
     
         6 . A system for stepwise varying fluid flow in a well, the system comprising a downhole valve assembly that can be switched between a first position in which fluid flow is permitted and a second position in which fluid flow is inhibited, wherein the valve assembly comprises a plurality of valves which each comprise an orifice through which a limited flow of fluid is allowed when the valve is in the second position thereof.  
     
     
         7 . The system of  claim 6 , wherein the valves are mounted on a common carrier body which can be lowered into the well through the production tubing and which is provided with a shoulder that can be landed in a nipple to seal off an annular space between carrier body and the tubing.  
     
     
         8 . The system of  claim 7 , wherein the valves have openings in which valve bodies are rotatably arranged, which openings form a longitudinal fluid passageway through the centre of the carrier body.  
     
     
         9 . The system of  claim 8 , wherein the valves are ball valves having each a first orifice and a second orifice which is oriented in a direction orthogonal to the first orifice and which is smaller than the first orifice.  
     
     
         10 . The system of  claim 9 , wherein the carrier body carries at least four valves which each have a second orifice that forms a flow restriction different from the flow restrictions formed by the second orifices of the other valves.