Optimization of electromagnetic telemetry in non-vertical wells

Abstract

An electromagnetic telemetry system may include an electrically conductive member, a transmitter coupled to the electrically conductive member, the transmitter configured to induce an alternating current along the electrically conductive member, the alternating current representing encoded information, a first receiver coupled to the electrically conductive member, the first receiver configured to receive electromagnetic waves resulting from the alternating current, a second receiver positioned at a location apart from the first receiver, the second receiver configured to receive the electromagnetic waves resulting from the alternating current, and a receiver processing system communicatively coupled to the first receiver and the second receiver, the receiver processing system configured to process the electromagnetic waves received by the first receiver and the second receiver into a combined signal, and decode the combined signal.

What is claimed is: 
     
         1 . An electromagnetic telemetry system, comprising:
 an electrically conductive member;   a transmitter coupled to the electrically conductive member, the transmitter configured to induce an alternating current along the electrically conductive member, the alternating current representing encoded information;   a first receiver coupled to the electrically conductive member, the first receiver configured to receive electromagnetic waves resulting from the alternating current;   a second receiver positioned at a location apart from the first receiver, the second receiver configured to receive the electromagnetic waves resulting from the alternating current; and   a receiver processing system communicatively coupled to the first receiver and the second receiver, the receiver processing system configured to:
 process the electromagnetic waves received by the first receiver and the second receiver into a combined signal; and 
 decode the combined signal. 
   
     
     
         2 . The system of  claim 1 , wherein at least one of the first receiver and the second receiver is an electric dipole antenna. 
     
     
         3 . The system of  claim 1 , wherein at least one of the first receiver and the second receiver is a magnetometer. 
     
     
         4 . The system of  claim 1 , wherein processing the electromagnetic waves received by the first receiver and the second receiver comprises phase shifting the electromagnetic waves received by the second receiver. 
     
     
         5 . The system of  claim 1 , wherein the receiver processing system is further configured to determine an approximate location of the transmitter within a wellbore based on a strength or a phase of the electromagnetic waves received by at least one of the first receiver and the second receiver. 
     
     
         6 . (canceled) 
     
     
         7 . The system of  claim 1 , wherein the electrically conductive member is a drill string, a casing string, or a production tubing. 
     
     
         8 . The system of  claim 1 , wherein the electrically conductive member is positioned within a wellbore including a non-vertical portion and the transmitter is positioned within the non-vertical portion of the wellbore. 
     
     
         9 . A method for performing electromagnetic telemetry in a well system, the method comprising:
 transmitting, by a transmitter, an alternating current along an electrically conductive member, the alternating current representing encoded information;   receiving, at a first receiver coupled to the electrically conductive member, electromagnetic waves resulting from the alternating current;   receiving, at a second receiver positioned at a location apart from the first receiver, the electromagnetic waves resulting from the alternating current;   generating a combined signal by combining the electromagnetic waves received by the first receiver and the second receiver; and   decoding the combined signal.   
     
     
         10 . The method of  claim 9 , wherein at least one of the first receiver and the second receiver is an electric dipole antenna. 
     
     
         11 . The method of  claim 9 , wherein at least one of the first receiver and the second receiver is a magnetometer. 
     
     
         12 . The method of  claim 9 , wherein generating the combined signal comprises phase shifting the electromagnetic waves received by the second receiver. 
     
     
         13 . The method of  claim 9 , further comprising changing the location of the second receiver as the transmitter moves to increase a strength of the electromagnetic waves at the second receiver. 
     
     
         14 . The method of  claim 9 , further comprising determining an approximate location of the transmitter based on a strength or a phase of the electromagnetic waves received by at least one of the first receiver and the second receiver. 
     
     
         15 . (canceled) 
     
     
         16 . The method of  claim 9 , wherein the electrically conductive member is a drill string, a casing string, or a production tubing. 
     
     
         17 . The method of  claim 9 , wherein the electrically conductive member is positioned within a wellbore including a non-vertical portion and the transmitter is positioned within the non-vertical portion of the wellbore. 
     
     
         18 . An electromagnetic telemetry system, comprising:
 an electrically conductive member;   a transmitter coupled to the electrically conductive member, the transmitter configured to induce an alternating current along the electrically conductive member;   an array of receivers configured to receive electromagnetic waves resulting from the alternating current;   a receiver processing system communicatively coupled to the array of receivers, the receiver processing system configured to determine an approximate location of the transmitter based on the electromagnetic waves received by the array of receivers.   
     
     
         19 . The system of  claim 18 , wherein the approximate location of the transmitter is determined by a strength or a phase of the electromagnetic waves received by the array of receivers. 
     
     
         20 . (canceled) 
     
     
         21 . The system of  claim 18 , wherein the array of receivers are arranged in rows and columns at a surface above a formation surrounding a wellbore. 
     
     
         22 . The system of  claim 21 , wherein the rows are oriented approximately parallel to a non-vertical portion of the wellbore. 
     
     
         23 . The system of  claim 18 , wherein the receiver processing system is further configured to determine the approximate location of the transmitter based on an electromagnetic property of a formation surrounding the electrically conductive member. 
     
     
         24 . (canceled) 
     
     
         25 . A method for determining an approximate location of a transmitter, the method comprising:
 transmitting, by a transmitter, an alternating current along an electrically conductive member within a wellbore including a non-vertical portion within a formation;   receiving electromagnetic waves resulting from the alternating current at an array of receivers located at a surface above the formation; and   determining an approximate location of the transmitter within the wellbore based on the electromagnetic waves received by the array of receivers.   
     
     
         26 . The method of  claim 25 , wherein the approximate location of the transmitter within the wellbore is determined by a strength or a phase of the electromagnetic waves received by the array of receivers. 
     
     
         27 . (canceled) 
     
     
         28 . The method of  claim 25 , wherein the array of receivers are arranged in rows and columns. 
     
     
         29 . (canceled) 
     
     
         30 . The method of  claim 25 , further comprising moving the array of receivers closer to the transmitter as the transmitter moves within the wellbore. 
     
     
         31 . The method of  claim 25 , wherein the receiver processing system is further configured to determine the approximate location of the transmitter based on an electromagnetic property of the formation.