Downhole communication

Abstract

Downhole electrical energy harvesting and communication in systems for well installations having metallic structure carrying electric current, for example CP current. In some instances there is a harvesting module (4) electrically connected to the metallic structure (2) at a first location and to a second location spaced from the first location, the first and second locations being chosen such that, in use, there is a potential difference therebetween due to the electric current flowing in the structure (2); and the harvesting module (4) being arranged to harvest electrical energy from the electric current. In addition or alternatively, there may be communication apparatus (4, 5, 6) for communication by modulation of the current, for example CP current, in the metallic structure (2).

1 . Downhole data communication apparatus for use in a well installation having metallic structure provided with a cathodic protection system such that there is an electrical circuit comprising the metallic structure and an earth return around which an electrical current flows as a result of the cathodic protection system, the downhole data communication apparatus comprising:
 a first communication module for location at a first location and comprising modulation means for modulating the electrical current at a first location so as to encode data; and   a second communication module for location at a second location, spaced from the first location, and comprising a detector for detecting the effect of the modulation of the electrical current at the first location so as to extract said data.   
     
     
         2 . Downhole data communication apparatus according to  claim 1  in which the modulation means is arranged to at least one of:
 i) where the cathodic protection system is an impressed cathodic protection system, control a signal source of the impressed cathodic protection system to directly modulate the cathodic protection current applied to the metallic structure; 
 ii) modify the connection between at least one anode of the cathodic protection system and the metallic structure; and 
 iii) alter the impedance of the electrical circuit. 
 
     
     
         3 . Downhole data communication apparatus according to  claim 1  wherein the first communication module is arranged for location downhole. 
     
     
         4 . Downhole data communication apparatus according to  claim 1  wherein the second communication module is arranged for location downhole. 
     
     
         5 . Downhole data communication apparatus according to  claim 1  comprising a sensor module for sensing at least one parameter, wherein the first communication module is arranged for sending data encoding readings from the sensor module towards the second communication module. 
     
     
         6 . Downhole data communication apparatus according to  claim 5  wherein the sensor module comprises a pressure sensor. 
     
     
         7 . Downhole data communication apparatus according to  claim 1  wherein the second communication module is arranged for providing data to a downhole device in dependence on data received by the second communication module from the first communication module. 
     
     
         8 . Downhole data communication apparatus according to  claim 7 , wherein the downhole device comprises at least one of:
 a downhole sensor;   a downhole actuator;   an annular sealing device, for example a packer, or a packer element;   a valve;   a downhole communication module, for example a transceiver or repeater.   
     
     
         9 . Downhole data communication apparatus according to  claim 8 , wherein the valve comprises at least one of:
 a subsurface safety valve;   a bore flow control valve;   a bore to annulus valve;   an annulus to annulus valve;   a bore to pressure compensation chamber valve;   an annulus to pressure compensation chamber valve;   a through packer or packer bypass valve.   
     
     
         10 . Downhole data communication apparatus according to  claim 1  wherein at least one of the first and second communication modules comprises a communications repeater for location downhole in a well and arranged for communicating with a first device beyond the well head using a communication channel which is wireless at least through the well head and arranged for communicating with second device located in the well and thus below the well head such that the communications repeater may act as a repeater between the first and second devices. 
     
     
         11 . Downhole data communication apparatus according to  claim 1  comprising a downhole electrical power harvesting module arranged for electrical connection between two spaced locations in a well installation and comprising an electrical circuit arranged for harvesting electrical energy, in use, from a potential difference between the spaced locations, used for harvesting, which acts as an input voltage, the harvesting module being arranged for supplying power to at least one component of the communication apparatus. 
     
     
         12 . Downhole data communication apparatus according to  claim 11  in which the first communication module is arranged for controlling the load generated by the harvesting module to cause said modulation of the electric current in the metallic structure at the signalling location. 
     
     
         13 . Downhole data communication apparatus according to  claim 11  wherein the harvesting module is arranged to harvest electrical energy from dc currents. 
     
     
         14 . A downhole data communication system comprising downhole data communication apparatus according to  claim 1  located in a well installation having metallic structure provided with a cathodic protection. 
     
     
         15 . A downhole data communication system for use in a well installation having metallic structure provided with a cathodic protection system such that there is an electrical circuit comprising the metallic structure and an earth return around which an electrical current flows as a result of the cathodic protection system, the system comprising downhole data communication apparatus comprising:
 a first communication module located at a first location and comprising modulation means for modulating the electrical current at the first location so as to encode data; and   a second communication module located at a second location, spaced from the first location, and comprising a detector for detecting the effect of the modulation of the electrical current at the first location so as to extract said data.   
     
     
         16 . A downhole data communication system according to  claim 14 , wherein the well is a subsea well. 
     
     
         17 . A downhole data communication system according to  claim 14  wherein the apparatus comprises a downhole electrical power harvesting module electrically connected between two spaced locations in the well installation and comprising an electrical circuit arranged for harvesting electrical energy, in use, from a potential difference between the spaced locations, used for harvesting, which acts as an input voltage, the harvesting module being arranged for supplying power to at least one component of the communication apparatus. 
     
     
         18 . A downhole data communication system according to  claim 17  wherein the current flow within portions of the metallic structure in regions between the spaced locations, used for harvesting, is in the same longitudinal direction. 
     
     
         19 . A downhole data communication system according to  claim 17  wherein there is an uninterrupted current flow path between the spaced locations, used for harvesting, which is at least partly via the metallic structure. 
     
     
         20 . A downhole data communication system according to  claim 14 , wherein at least one of the first communication module and the second communication module is located in an enclosed annulus of the well. 
     
     
         21 . A downhole data communication system according to  claim 14  comprising a pressure sensor arranged for monitoring the reservoir pressure of the well. 
     
     
         22 . A downhole data communication system according to  claim 14  comprising a pressure sensor arranged for monitoring the pressure in an annulus of the well. 
     
     
         23 . A downhole data communication system according to  claim 14  comprising a pressure sensor arranged for monitoring the pressure in an enclosed annulus of the well.