System for controlling cement flow in a well

Abstract

A method for preventing undesired cement flow in a well containing a tubing string, comprises: determining a desired pressure drop for a desired flow rate at a desired location in the tubing string, determining a flow area that will cause the desired pressure drop, and installing in the tubing string a choke having at least one port, wherein the total area of the port or ports equals the desired flow area. The choke may include at least two ports, one of which may include a least one rupture disk disposed selected to rupture when the pressure drop across the choke exceeds a predetermined value. The choke may be below a float collar in the well. The invention allows the use of foamed cement and in particular foamed cement having a density that is less than the lowest density that could have been used if the choke were not in place.

What is claimed is: 
     
         1 . A method for preventing undesired cement flow in a well containing a tubing string, comprising the steps of:
 a) determining a desired pressure drop for a desired flow rate at a desired location in the tubing string;   b) determining a flow area that will cause the desired pressure drop; and   c) installing in the tubing string a choke having at least one port, wherein the total cross-sectional area of the port or ports equals the desired flow area.   
     
     
         2 . The method according to  claim 1  wherein the choke includes at least two ports. 
     
     
         3 . The method according to  claim 1  wherein the choke includes at least one rupture disk disposed in a port and at least one port that is unobstructed. 
     
     
         4 . The method according to  claim 3  wherein the rupture disk is selected to rupture when the pressure drop across the choke exceeds a predetermined value. 
     
     
         5 . The method according to  claim 1  wherein step c) comprises installing the choke below a float collar in the well. 
     
     
         6 . The method according to  claim 1 , further including the step of:
 d) cementing the well using foamed cement.   
     
     
         7 . The method according to  claim 6  wherein the foamed cement has a density that is less than the lowest density that could have been used if the choke were not in place. 
     
     
         8 . The method according to  claim 1  wherein the desired pressure drop is in the range of between 100 (0.69 MPa) and 1000 psi (6.9 MPa). 
     
     
         9 . The method according to  claim 1  wherein at least one port can be actuated from a closed mode to an open mode.