Method of detecting signals in acoustic drill string telemetry

Abstract

A method of acoustic telemetry in a drill string in a wellbore, comprises transmitting an acoustic signal related to a parameter of interest from a transmitting location into the drill string. The signals propagated through the drill string are detected at a receiving location, where the detected signals include noise. A drill string transfer matrix is determined defining the propagation of signals through a transfer interval between the receiving location and the transmitting location. The detected signals and the drill string transfer matrix are used for obtaining an estimate of the acoustic signal.

What is claimed is:  
     
         1 . A method of acoustic telemetry in a drill string in a wellbore, comprising: 
 a. transmitting an acoustic signal related to a parameter of interest from a transmitting location into the drill string;    b. detecting signals propagated through the drill string at a receiving location, said detected signals including noise;    c. determining a drill string transfer matrix defining the propagation of signals through a transfer interval between the receiving location and the transmitting location; and    d. using said detected signals and the drill string transfer matrix for obtaining an estimate of the acoustic signal.    
     
     
         2 . The method of  claim 1  wherein detecting signals at a receiving location comprises detecting a first time-series of measurements related to a force on said drill string and a second time-series of measurements related to a motion of said drill string.  
     
     
         3 . The method of  claim 2  wherein using said detected signals and the drill string transfer matrix for obtaining an estimate of the acoustic signal comprises: 
 a. transforming said first time-series of measurements and said second time-series of measurements to a frequency domain;  
 b. combining said transformed first time-series of measurements and said transformed second time-series measurements with said transfer matrix to generate an inferred force related signal at said second location and an inferred motion related signal at said second location;  
 c. transforming said inferred force related signal and said inferred motion related signal to the time domain generating an inferred time-series force at said second location and an inferred time-series motion at said second location; and  
 d. decoding said inferred force signal and said inferred motion signal to determine said transmitted parameter of interest.  
 
     
     
         4 . The method of  claim 1  wherein determining the drill string transfer matrix comprises: 
 i. inputting data related to mechanical properties and material properties for each of a plurality of sections of the drill string;  
 ii. calculating for each of the plurality of sections of the drill string, a transfer matrix related to each section of the drill string; and  
 iii. combining each of the plurality of section transfer matrices with each succeeding section transfer matrix.  
 
     
     
         5 . The method of  claim 1  wherein the transmitting location is a downhole location proximate a bottom end of the drill string and said receiving location is proximate a top end of the drill string.  
     
     
         6 . The method of  claim 1  wherein the transmitting location is proximate a top end of the drill string and the receiving location is downhole proximate a bottom end of the drill string.  
     
     
         7 . The method of  claim 2 , wherein the measurement related to drill string motion is one of (i) an acceleration, (ii) a velocity, and (iii) a displacement.  
     
     
         8 . The method of  claim 2  wherein using said detected signals and the drill string transfer matrix for obtaining an estimate of the acoustic signal comprises: 
 i. transforming said transfer matrix to a time domain;  
 ii. combining said first time-series of measurements and said second time-series of measurements with said transformed transfer matrix to generate an inferred force related signal at said second location and an inferred motion related signal at said second location; and  
 iii. decoding said inferred force signal and said inferred motion signal to determine said transmitted parameter of interest.  
 
     
     
         9 . The method of  claim 3 , wherein the step of transforming said first time-series of measurements and said second time-series of measurements includes windowing said first time-series of measurements and said second time-series of measurements.  
     
     
         10 . The method of  claim 3 , wherein the step of transforming said inferred force related signal and said inferred motion related signal to the time domain includes band-limiting said inferred force related signal and said inferred motion related signal in the frequency domain before transformation to the time domain.  
     
     
         11 . A method of reducing noise in an acoustic signal transmitted at a second location and received at a first location in a drill string, comprising: 
 a. calculating a transfer matrix related to a transmission interval of the drill string;    b. detecting time series data sets of vibrations at said first location comprising a first time-series data set of measurements related to a force on said drill string and a second time-series data set of measurements related to an acceleration of said drill string;    c. transforming said first time-series data set and said second time-series data set to a frequency domain;    d. combining said transformed first time-series data set and said transformed second time-series data set with said transfer function to generate an inferred force related signal at said second location and an inferred acceleration related signal at said second location; and    e. transforming said inferred force related signal and said inferred acceleration related signal to the time domain generating an inferred time-series of force at said second location and an inferred time-series of acceleration at said second location.    
     
     
         12 . The method of  claim 11  wherein calculating the drill string transfer matrix comprises: 
 i. calculating for each of a plurality of drill string sections, a transfer matrix related to each section of the drill string; and  
 ii. combining each of the plurality of section transfer matrices with each succeeding section transfer matrix.  
 
     
     
         13 . The method of  claim 11  wherein the second transmitting location is a downhole location proximate a bottom end of the drill string and said first receiving location is proximate a top end of the drill string.  
     
     
         14 . The method of  claim 11  wherein the second transmitting location is proximate a top end of the drill string and the first receiving location is downhole proximate a bottom end of the drill string.