Downhole bha seismic signal generator

Abstract

A method for performing a seismic investigation during subterranean drilling operations includes connecting a bottom hole assembly to a drill string. The bottom hole assembly includes a drill bit and a vibration damper. The drill string is lowered into a borehole and rotated to drill the borehole to a greater length with the drill bit. An actual vibration generated by the bottom hole assembly is measured with a control system and the actual vibration is compared to a target seismic vibration range. When the actual vibration is outside of the target seismic vibration range, the dampening coefficient of the vibration damper is changed.

What is claimed is: 
     
         1 . A method for performing a seismic investigation during subterranean drilling operations, the method comprising:
 (a) connecting a bottom hole assembly to a drill string, the bottom hole assembly comprising a drill bit and a vibration damper;   (b) lowering the drill string into a borehole and rotating the drill string to drill the borehole to a greater length with the drill bit;   (c) measuring an actual vibration generated by the bottom hole assembly with a control system;   (d) comparing the actual vibration to a target seismic vibration range;   (e) changing the dampening coefficient of the vibration damper when the actual vibration is outside of the target seismic vibration range; and   (f) repeating steps (c) through (e) until the actual vibration generated by the bottom hole assembly is within the target seismic vibration range.   
     
     
         2 . The method of  claim 1 , further comprising sensing a return seismic signal returned from a subterranean feature from a source seismic signal generated by the bottom hole assembly with a plurality of sensors to image a formation around and ahead of the drill bit, the plurality of sensors being located on one selected from a group consisting of along the drill string, attached to a casing, in an adjacent borehole, and at a surface. 
     
     
         3 . The method of  claim 2 , wherein the plurality of sensors are selected from a group consisting of multi-component seismic sensors and pressure sensors. 
     
     
         4 . The method of  claim 2 , wherein the plurality of sensors includes at least three 3-component seismic sensors. 
     
     
         5 . The method of  claim 2 , further comprising after sensing the return seismic signal, comparing the actual vibration to a target performance vibration and changing the dampening coefficient of the vibration damper when the actual vibration exceeds the target performance vibration. 
     
     
         6 . The method of  claim 1 , further comprising repeating steps (c) through (e) until a target borehole length is reached with the drill bit. 
     
     
         7 . The method of  claim 1 , wherein the vibration damper includes a magneto rheological dampening fluid and step (e) comprises generating a control signal with the control system to change the viscosity of the magneto rheological dampening fluid. 
     
     
         8 . The method of  claim 1 , wherein the vibration damper comprises a damping piston having one or more adjustable orifices and wherein changing the dampening coefficient of the vibration damper comprises generating a control signal using the control system and using the control signal to change the cross sectional area of the adjustable orifices. 
     
     
         9 . The method of  claim 1 , wherein the bottom hole assembly further comprises the control system and changing the dampening coefficient of the vibration damper comprises changing the dampening coefficient of the vibration damper with the control system. 
     
     
         10 . The method of  claim 1 , wherein the control system is located outside of the borehole and changing the dampening coefficient of the vibration damper comprises changing the dampening coefficient of the vibration damper with the control system. 
     
     
         11 . The method of  claim 1 , wherein:
 the step of measuring the actual vibration comprises measuring a frequency of the actual vibration;   the step of comparing the actual vibration to the target seismic vibration range comprises comparing the frequency of the actual vibration to a target frequency range of seismic vibration; and   the step of changing the dampening coefficient of the vibration damper when the actual vibration is outside of the target seismic vibration range, comprises changing the dampening coefficient of the vibration damper when the frequency of the actual vibration is outside of the target frequency range of seismic vibration.   
     
     
         12 . A method for performing a seismic investigation during subterranean drilling operations, the method comprising:
 (a) connecting a bottom hole assembly to a drill string, the bottom hole assembly comprising a drill bit and a vibration damper;   (b) lowering the drill string into a borehole and rotating the drill string to drill the borehole to a greater length with the drill bit;   (c) selecting a target vibration range from a group consisting of a target seismic vibration range and a target performance vibration range, the target seismic vibration range including vibrations that generate a source seismic signal and the target performance vibration range including vibrations that improve a drilling performance;   (d) measuring an actual vibration generated by the bottom hole assembly with a control system;   (e) comparing the actual vibration to the target vibration range;   (f) changing the dampening coefficient of the vibration damper when the actual vibration is outside of the target vibration range; and   (g) repeating steps (d) through (f) until the actual vibration generated by the bottom hole assembly is within the target seismic vibration range.   
     
     
         13 . The method of  claim 12 , further comprising repeating steps (d) through (f) until a target borehole length is reached with the drill bit. 
     
     
         14 . The method of  claim 12 , wherein step (c) comprises selecting the seismic vibration range, the method further comprising sensing a return seismic signal that has returned from a subterranean feature with a plurality of sensors. 
     
     
         15 . The method of  claim 12 , wherein the vibration damper includes a magneto rheological dampening fluid and step (f) comprises generating a control signal with the control system to change the viscosity of the magneto rheological dampening fluid. 
     
     
         16 . The method of  claim 12 , wherein the control system is located outside of the borehole and selecting a target vibration range comprises selecting a target vibration range with the control system. 
     
     
         17 . An apparatus for performing a seismic investigation during subterranean drilling operations, the apparatus comprising:
 a bottom hole assembly connected to a drill string, the bottom hole assembly comprising a drill bit and a vibration damper; and   a control system operable for selectively measuring an actual vibration generated by the bottom hole assembly, comparing the actual vibration to a target vibration range, and changing the dampening coefficient of the vibration damper when the actual vibration is outside of the target vibration range until the actual vibration generated by the bottom hole assembly is within the target seismic vibration range.   
     
     
         18 . The apparatus of  claim 17 , wherein the vibration damper comprises a magneto rheological dampening fluid, wherein changing the viscosity of the magneto rheological dampening fluid changes the dampening coefficient of the vibration damper. 
     
     
         19 . The apparatus of  claim 17 , wherein the vibration damper comprises a piston and dampening fluid, wherein the piston includes at least one adjustable orifice, and varying the cross sectional area of the at least one adjustable orifice is operable to change the dampening coefficient of the vibration damper. 
     
     
         20 . The apparatus of  claim 17 , further comprising a communication means for transmitting signals between the control system and the bottom hole assembly, the communication means selected from a group consisting of mud pulse telemetry, acoustic telemetry, electro magnetic telemetry, or wired drill pipe. 
     
     
         21 . The apparatus of  claim 17 , further comprising a plurality of sensors for sensing a return seismic signal that has returned from a subterranean feature. 
     
     
         22 . The apparatus of  claim 17 , further comprising at least three 3-component seismic sensors for sensing a return seismic signal that has returned from a subterranean feature. 
     
     
         23 . The apparatus of  claim 17 , wherein the control system further comprises a selector for switching the target vibration means between a target seismic vibration range and a target performance vibration range, the target seismic vibration range including vibrations that generate a seismic signal and the target performance vibration range including vibrations that improve a drilling performance.