Selective multi-stage cementing of casing

Abstract

An apparatus and a method for cementing a casing in various elevations is disclosed. A casing string having at least one cementing valve is lowered into a borehole. In the closed position, the valve prevents fluid communication between the interior and exterior of the casing. In the opened position, the valve allows fluid communication between the interior and the exterior of the casing so that cement is pumped therethrough to cement the borehole adjacent the valve at the borehole elevation where the valve is located. Opening of the valve is effected by landing on the valve an opening dart having a unique profile corresponding to the valve and applying pressure on the dart to move a sleeve in the valve to a first position exposing radial ports in the casing. The valve is closed by landing a dart on the opening dart and applying pressure thereon to move the sleeve to a second position to close the ports.

What is claimed is: 
     
         1 . A method for selectively cementing a casing, comprising:
 locating a first valve having a first valve unique profile in the casing;   delivering a first object having a matching profile to the first valve unique profile for sealingly landing on the first valve;   moving the first valve with said first object with pressure to open a first casing port through the casing, the first casing port extending from the interior of the casing to the exterior of the casing;   flowing cement from the interior of the casing to the exterior of the casing through the first casing port; and   closing the first casing port.   
     
     
         2 . The method according to  claim 1  wherein the step of closing the first casing port includes the steps of:
 delivering a second object for sealingly landing on the first valve; and 
 moving the first valve with the second object with pressure to close the first casing port. 
 
     
     
         3 . The method according to  claim 1  further including the steps of:
 locating a second valve having a second valve unique profile in the casing; 
 delivering a third object having a matching profile to the second valve unique profile for sealingly landing on the second valve; 
 moving the second valve with the second object with pressure to open a second casing port through the casing, the second casing port extending from the interior of the casing to the exterior of the casing; 
 flowing cement from the interior of the casing to the exterior of the casing through the second casing port; and 
 closing the second casing port. 
 
     
     
         4 . The method according to  claim 3  wherein the step of closing the second casing port includes the steps of:
 delivering a fourth object for sealingly landing on the second valve; and 
 moving the second valve with the fourth object with pressure to close the first casing port.