Apparatus and Method for Selectively Placing Additives in Wellbore Cement

Abstract

An apparatus for releasing additive into cement pumped into an annular space between a wall of a wellbore and a casing inserted into the wellbore include a cement additive enclosed in a container disposed in the annular space at at least one selected position along the wellbore. The container is configured to release the additive at a selected time.

1 . An apparatus for releasing additive into cement pumped into an annular space between a wall of a wellbore and a casing inserted into the wellbore, comprising:
 a cement additive enclosed in a container disposed in the annular space at at least one selected position along the wellbore, wherein the container is configured to release the additive at a selected time.   
     
     
         2 . The apparatus of  claim 1  wherein the container comprises a material that is chemically reactive with a component of pumped cement. 
     
     
         3 . The apparatus of  claim 2  wherein the chemical reaction comprises one of an exothermic reaction, reaction to pH of a component of the pumped cement and solution. 
     
     
         4 . The apparatus of  claim 1  wherein the container is configured to discharge the cement additive therefrom on application of a control signal. 
     
     
         5 . The apparatus of  claim 4  wherein the control signal is at least one of mechanical and electrical. 
     
     
         6 . The apparatus of  claim 1  further comprising a casing centralizer disposed proximate the container. 
     
     
         7 . The apparatus of  claim 6  wherein the centralizer comprises spiral blades or vanes. 
     
     
         8 . A method for releasing an additive to cement pumped into an annular space between a wall of a wellbore and a casing inserted into the wellbore, comprising:
 disposing the additive in a container in the annular space;   pumping cement through the wellbore and into the annular space; and   releasing the additive from the container at a selected time.   
     
     
         9 . The method of  claim 8  wherein the container comprises a material that is chemically reactive with a component of pumped cement. 
     
     
         10 . The method of  claim 9  wherein the chemical reaction comprises one of an exothermic reaction, reaction to pH of a component of the pumped cement and solution. 
     
     
         11 . The method of  claim 8  wherein the container is configured to discharge the cement additive therefrom on application of a control signal. 
     
     
         12 . The apparatus of  claim 11  wherein the control signal is at least one of mechanical and electrical. 
     
     
         13 . The method of  claim 8  further comprising disposing a casing centralizer disposed proximate the container. 
     
     
         14 . The method of  claim 13  wherein the centralizer comprises spiral blades or vanes