Electromagnetic telemetry system

Abstract

An electromagnetic telemetry (EMT) system is provided. A downhole transceiver sub is coupled with a downhole tool. The downhole transceiver sub and the downhole tool positioned in a wellbore having a casing extending along a length of the wellbore. The downhole transceiver sub transmits data from the downhole tool by passing a current through the casing to radiate electromagnetic fields. An uphole transceiver sub is disposed uphole from the downhole transceiver sub. The uphole transceiver sub is operable to measure the electromagnetic fields. The measured electromagnetic fields are decoded to obtain the data from the downhole tool.

What is claimed is: 
     
         1 . An electromagnetic telemetry (EMT) system comprising:
 a downhole transceiver sub operable to be coupled with a downhole tool, the downhole transceiver sub and the downhole tool operable to be positioned in a wellbore having a casing extending along a length of the wellbore, the downhole transceiver sub operable to transmit data from the downhole tool by passing a current through the casing to radiate electromagnetic fields; and   an uphole transceiver sub operable to be disposed uphole from the downhole transceiver sub, the uphole transceiver sub is operable to measure the electromagnetic fields,   wherein the measured electromagnetic fields are decoded to obtain the data from the downhole tool.   
     
     
         2 . The EMT system of  claim 1 , wherein the downhole transceiver sub further comprises:
 a first electrode operable to be in contact with the casing, and   a second electrode operable to be in contact with the casing a distance uphole from the first electrode, wherein the current is passed between the first electrode and the second electrode through the casing to form an electric dipole which radiates the electromagnetic fields.   
     
     
         3 . The EMT system of  claim 2 , wherein the downhole transceiver sub further includes a voltmeter coupled with the first electrode and the second electrode to measure a voltage between the first electrode and the second electrode of the downhole transceiver sub. 
     
     
         4 . The EMT system of  claim 2 , wherein the distance between the first electrode and the second electrode of the downhole receiver sub is between about 5 feet and about 30 feet. 
     
     
         5 . The EMT system of  claim 1 , wherein the uphole transceiver sub further comprises:
 a first electrode, and   a second electrode, the second electrode being disposed a distance from the first electrode, wherein the electromagnetic fields are measured by the voltage between the first electrode and the second electrode of the uphole transceiver sub.   
     
     
         6 . The EMT system of  claim 5 , wherein the first electrode of the uphole transceiver sub is operable to be in contact with the casing, and the second electrode of the uphole transceiver sub is operable to be in contact with the ground. 
     
     
         7 . The EMT system of  claim 5 , wherein the uphole transceiver sub further includes a voltmeter coupled with the first electrode and the second electrode to measure a voltage between the first electrode and the second electrode of the uphole transceiver sub. 
     
     
         8 . The EMT system of  claim 1 , further comprising one or more intermediate subs operable to be disposed between the downhole transceiver sub and the uphole transceiver sub, the one or more intermediate subs each including a first electrode operable to be in contact with the casing and a second electrode operable to be in contact with the casing a distance uphole from the first electrode, wherein the one or more intermediate subs are operable to be function as signal amplifiers. 
     
     
         9 . The EMT system of  claim 1 , further comprising a processor coupled with the uphole transceiver sub, the processor configured to determine the data by demodulating the measured magnetic fields. 
     
     
         10 . A system comprising:
 a conveyance disposed within a wellbore having a casing extending along a length of the wellbore;   a downhole tool coupled with the conveyance;   an electromagnetic telemetry (EMT) system coupled with the downhole tool, the EMT system operable to transmit information from the downhole tool, the EMT system comprising:
 a downhole transceiver sub coupled with a downhole tool, the downhole transceiver sub and the downhole tool positioned in a wellbore having a casing extending along a length of the wellbore, the downhole transceiver sub transmitting data from the downhole tool by passing a current through the casing to radiate electromagnetic fields; and 
 an uphole transceiver sub disposed uphole from the downhole transceiver sub, the uphole transceiver sub is operable to measure the electromagnetic fields, 
   wherein the measured electromagnetic fields are decoded to obtain the data from the downhole tool.   
     
     
         11 . The system of  claim 10 , wherein the downhole transceiver sub further comprises:
 a first electrode in contact with the casing, and   a second electrode in contact with the casing a distance uphole from the first electrode, wherein the current is passed between the first electrode and the second electrode through the casing to form an electric dipole which radiates the electromagnetic fields.   
     
     
         12 . The system of  claim 10 , wherein the uphole transceiver sub further comprises:
 a first electrode, and   a second electrode, the second electrode being disposed a distance from the first electrode, wherein the electromagnetic fields are measured by the voltage between the first electrode and the second electrode of the uphole transceiver sub.   
     
     
         13 . The system of  claim 12 , wherein the first electrode of the uphole transceiver sub is in contact with the casing, and the second electrode of the uphole transceiver sub is in contact with the ground. 
     
     
         14 . The system of  claim 12 , wherein the uphole transceiver sub further includes a voltmeter coupled with the first electrode and the second electrode to measure a voltage between the first electrode and the second electrode of the uphole transceiver sub. 
     
     
         15 . The system of  claim 10 , further comprising one or more intermediate subs coupled with the conveyance and disposed between the downhole transceiver sub and the uphole transceiver sub, the one or more intermediate subs each including a first electrode in contact with the casing and a second electrode in contact with the casing a distance uphole from the first electrode, wherein the one or more intermediate subs function as signal amplifiers. 
     
     
         16 . The system of  claim 10 , further comprising a processor coupled with the uphole transceiver sub, the processor configured to determine the data by demodulating the measured magnetic fields. 
     
     
         17 . A method to use an electromagnetic telemetry (EMT) system, the method comprising:
 creating an electric dipole which radiates electromagnetic fields to transmit data using a downhole transceiver sub disposed in a wellbore;   measuring the magnetic fields by an uphole transceiver sub which is positioned uphole from the downhole transceiver sub; and   determining, by a processor, the data by decoding the measured magnetic fields.   
     
     
         18 . The method of  claim 17 , wherein creating an electric dipole includes passing a current between a first electrode of a downhole transceiver sub and a second electrode of the downhole transceiver sub through the casing, the first electrode in contact with the casing, and the second electrode of the downhole transceiver sub in contact with the casing a distance uphole from the first electrode,
 wherein measuring the magnetic fields includes measuring a voltage between a first electrode and a second electrode of the uphole transceiver sub.   
     
     
         19 . The method of  claim 17 , further comprising:
 disposing a conveyance in the wellbore, a downhole tool being coupled with the conveyance, the downhole transceiver sub being coupled with the downhole tool;   transmitting the data from the downhole tool to the downhole transceiver sub.   
     
     
         20 . The method of  claim 17 , further comprising:
 amplifying the magnetic fields using one or more intermediate subs coupled with the conveyance and disposed between the downhole transceiver sub and the uphole transceiver sub, the one or more intermediate subs each including a first electrode in contact with the casing and a second electrode in contact with the casing a distance uphole from the first electrode.