Retrievable downhole heater

Abstract

The present invention provides a retrievable downhole heater that can readily be retrieved from a downhole location once it has been used. The heater comprises an elongate tubular body ( 3 ) with a heat source ( 11 ) housed therein. The tubular body is formed from a material that does not melt during the downhole operation of the heater. The heater also is provided with at least one reduced friction region ( 13 ) that has a lower co-efficient of friction than the material from which the tubular body is formed. The reduced friction regions of the heater are configured to retain the lower co-efficient of friction following the downhole operation of the heater.

1 . A retrievable downhole heater comprising an elongate tubular body with a heat source housed therein, said tubular body being formed from a material that does not melt during the downhole operation of the heater; and
 wherein the heater is provided with at least one reduced friction region having a lower co-efficient of friction than the material from which the tubular body is formed and whereby each reduced friction region is configured to retain the lower co-efficient of friction following the downhole operation of the heater.   
     
     
         2 . The heater of  claim 1 , wherein at least one reduced friction region on the heater comprises one or more rotatable bearings that project beyond the outer surface of the elongate tubular body. 
     
     
         3 . The heater of  claim 2 , comprising one or more rotatable bearings projecting from the outer surface of the elongate tubular body. 
     
     
         4 . The heater of  claim 2 , wherein one or more rotatable bearings are mounted on a sub that is attached to the leading and/or trailing end of the elongate tubular body. 
     
     
         5 . The heater of  claim 4 , wherein the sub is provided in the form of an open-ended skirt portion that extends from the leading end of the heater. 
     
     
         6 . The heater of  any one of the preceding claims , wherein at least one reduced friction region on the heater comprises one or more contact surfaces formed from a material that has a lower co-efficient of friction than the material from which the tubular body is formed and whereby each contact surface projects outwards beyond the outer surface of the elongate tubular body. 
     
     
         7 . The heater of  claim 6 , wherein at least one contact surface is provided by a low friction component that is mounted on the outer surface of the elongate tubular body. 
     
     
         8 . The heater of  claim 6 or 7 , wherein at least one contact surface is provided by a low friction component that is mounted on a sub that is attached to the leading and/or trailing end of the elongate tubular body 
     
     
         9 . The heater of  claim 7 or 8 , wherein said component is annular-shaped. 
     
     
         10 . The heater of  any of the preceding claims , wherein at least one reduced friction region on the heater comprises a friction reducing coating applied to the outer surface of the elongate tubular body. 
     
     
         11 . The heater of any one of  claims 1 to 10 , wherein said reduced friction region is provided at:
 a) a leading end of the heater, which, in use, is deployed downhole first;   b) a trailing end of the heater; and/or   c) a location on the elongate tubular body between the leading and trailing ends of the heater.   
     
     
         12 . The heater of any one of  claims 1 to 11 , wherein said reduced friction region extends over the entire outer surface of the elongate tubular body. 
     
     
         13 . The heater of  any of the preceding claims , wherein the heat source comprises a chemical reaction heat source. 
     
     
         14 . A downhole well plugging or sealing tool, said tool comprising:
 a heater in accordance with  any of the preceding claims ; and   an alloy, which can be melted downhole by the heater in order to form a plug or seal within a target region of a downhole environment.   
     
     
         15 . The tool of  claim 14 , wherein the tool further comprises a dump bailer and the pre-melted alloy is delivered downhole within the dump bailer in the form of alloy beads or shot. 
     
     
         16 . The tool of  claim 14 , wherein the pre-melted alloy is mounted on the outer surface of the elongate tubular body. 
     
     
         17 . The tool of  claim 16 , wherein the pre-melted alloy covers said at least one reduced friction region. 
     
     
         18 . The tool of  claim 16 , wherein the pre-melted alloy and said at least one reduced friction region are arranged on the outer surface of the elongate tubular body so that they do not overlap with one another. 
     
     
         19 . A method of manufacturing a retrievable downhole heater, said method comprising:
 providing an elongate tubular body formed from a material that does not melt during the operation of the heater; and   installing a heat source within the tubular body and providing at least one reduced friction region on heater;   wherein said reduced friction region has a lower co-efficient of friction than the material from which the tubular body is formed and is configured to retain said lower co-efficient of friction following the downhole operation of the heater.   
     
     
         20 . The method of  claim 19 , wherein the heat source installed within the tubular body of the heater is a chemical reaction heat source. 
     
     
         21 . The method of  claim 19 or 20 , wherein at least one reduced friction region is provided by mounting one or more rotatable bearings on the heater such that said bearings project beyond the outer surface of the elongate tubular body. 
     
     
         22 . The method of any one of  claims 19, 20 or 21 , wherein at least one reduced friction region is provided by applying a coating of a friction reducing agent to the outer surface of the elongate tubular body. 
     
     
         23 . The method of any one of  claims 19 to 22 , wherein at least one reduced friction region is provided by mounting a component formed from a material with a lower co-efficient of friction than the material used to form the elongate tubular body on the heater such that a contact surface of the component sits proud of the outer surface of the tubular body. 
     
     
         24 . The method of  claim 23 , wherein the component is annular-shaped. 
     
     
         25 . The method of any one of  claims 19 to 24 , wherein said reduced friction region is provided at:
 a) a leading end of the heater, which, in use, is deployed downhole first;   b) a trailing end of the heater; and/or   c) a location on the elongate tubular body between the leading and trailing ends of the heater.   
     
     
         26 . The method of any one of  claims 19 to 25 , wherein said reduced friction region extends over the entire outer surface of the elongate tubular body.