System and method for telemetry in a wellbore

Abstract

A method and apparatus for creating a telemetry signal in a drillstring is disclosed. Opposite torsional forces are imparted on the drillstring at two or more different locations. A steel shaft inside the drillstring is coupled to the drillstring via electromagnetic actuators at end and rigidly attached to the drillstring at the other end. A similar method and apparatus for generating axial telemetry signal in the drillstring is also disclosed.

What is claimed is:  
     
         1 . A method of creating a signal in a drillstring comprising the steps of: 
 imparting a first force on the drillstring at a first location; and    imparting a second force to the drillstring at a second location, the first force and the second force being in opposite directions.    
     
     
         2 . The method of  claim 1  wherein the first and second forces are torsional forces.  
     
     
         3 . The method of  claim 1  wherein the first and second forces are axial forces.  
     
     
         4 . The method of  claim 1  wherein the magnitude of the first and second forces are substantially equal.  
     
     
         5 . The method of  claim 1  further comprising the step imparting a third force on the drillstring at a third location, and the sum of forces imparted on the drill string is substantially equal to zero.  
     
     
         6 . The method of  claim 1  wherein the second force is imparted at a time delay after the first force is imparted.  
     
     
         7 . The method of  claim 6  further comprising generating an acoustic wave that propagates though a member that is coupled to the drillstring at the first and second locations and wherein the time delay depends upon the length and material properties of the member.  
     
     
         8 . The method of  claim 7  wherein the acoustic wave in the member is generated by a force that is equal and opposite to the first force.  
     
     
         9 . The method of  claim 8  wherein the member is rigidly attached to the drillstring at the second location.  
     
     
         10 . The method of  claim 9  wherein the member comprises a steel hollow shaft having a circular cross section and being positioned inside the drillstring.  
     
     
         11 . The method of  claim 7  wherein the first force and the acoustic wave in the member are generated using one or more electromagnetic actuators.  
     
     
         12 . The method of  claim 11  wherein the one or more electromagnetic actuators comprise one or more coils mounted to drillstring at the first location and one or more magnets mounted to the member.  
     
     
         13 . The method of  claim 1  wherein the drillstring is made primarily of steel, and wherein the relative movement in the drillstring between first location and the second location is due primarily to the elastic properties of the steel.  
     
     
         14 . The method of  claim 1  wherein the drillstring is a portion of drill collar.  
     
     
         15 . The method of  claim 1  further comprising the step of suppressing acoustic noise in the drillstring in a predetermined frequency band between the first location and the drill bit.  
     
     
         16 . The method of  claim 15  wherein the step of suppressing acoustic noise is accomplished using a device comprising adjacent zones of different acoustic impedances.  
     
     
         17 . The method of  claim 15  wherein the predetermined frequency band is a second pass band, and the forces imparted at the first and second locations generate acoustic signals within the second pass band.  
     
     
         18 . The method of  claim 1  further comprising the steps of: 
 receiving acoustic signals at the surface that have been generated by imparting forces at the first and second locations;  
 converting the acoustic signals into electromagnetic signals; and  
 recording the electromagnetic signals.  
 
     
     
         19 . The method of  claim 1  wherein the first and second locations are in a bottom hole assembly.  
     
     
         20 . The method of  claim 1  wherein the first and second locations are a substantial distance from the bit, and tools in a bottom hole assembly communicate with a receiver near the first and second locations via a cable.  
     
     
         21 . The method of  claim 20  wherein the drill string is a portion of drill pipe adapted so as to create telemetry signals.  
     
     
         22 . An apparatus for creating an acoustic signal on a drillstring located in a wellbore comprising: 
 a length of drill string having a first location and a second location; and    an elastic member coupled to the drill string so as to enable the application of a first force on the drillstring at the first location, and a second force on the drillstring at the second location, the first force and the second force being in opposite directions.    
     
     
         23 . The apparatus of  claim 22  wherein the first and second forces are torsional forces.  
     
     
         24 . The apparatus of  claim 22  wherein the first and second forces are axial forces.  
     
     
         25 . The apparatus of  claim 23  wherein the magnitude of the first and second forces are approximately equal.  
     
     
         26 . The apparatus of  claim 23  the member enables the application of third force on the drillstring at a third location, and the sum of forces applied to the drill string is substantially equal to zero.  
     
     
         27 . The apparatus of  claim 23  wherein the member is coupled to the drillstring at the first location with one or more electromagnetic actuators.  
     
     
         28 . The apparatus of  claim 27  wherein the member is coupled to the drillstring at the second location using a rigid attachment.  
     
     
         29 . The apparatus of  claim 28  wherein the one or more electromagnetic actuators comprise one or more coils mounted to drillstring at the first location and one or more magnets mounted to the member.  
     
     
         30 . The apparatus of  claim 29  wherein the member comprises a steel hollow shaft having a circular cross section and being positioned inside the drillstring.  
     
     
         31 . The apparatus of  claim 23  wherein the drillstring is made primarily of steel, and wherein the relative torsional movement in the drillstring between first location and the second location is due primarily to the elastic properties of the steel.  
     
     
         32 . The apparatus of  claim 23  further comprising a baffle located on the drillstring between the first location and the drill bit the baffle adapted and configured to suppress torsional waves in the drillstring in a predetermined frequency range.  
     
     
         33 . The apparatus of  claim 32  wherein the baffle comprises adjacent portions of material, each portion having a different acoustic impedance than each adjacent portion.  
     
     
         34 . The apparatus of  claim 33  wherein the predetermined frequency band is a second pass band, and the torsional forces imparted at the first and second locations generate torsional signals within the second pass band.