Continuous taring for downhole strain

Abstract

Some implementations include a method for eliminating bias in strain data produced by one or more strain gauges in a drill bit of a drill string. The method may include drilling a borehole with the drill bit. The method may include determining a bias in strain data based on drilling parameters detected during the drilling. The method may include removing the bias from a biased downhole drill bit measurement to indicate an unbiased downhole drill bit measurement.

What is claimed is: 
     
         1 . A method for eliminating bias in strain data produced by one or more strain gauges in a drill string, the method comprising:
 drilling a borehole with the drill string;   determining a bias in the strain data based on drilling parameters detected during the drilling; and   removing the bias from a biased downhole drill string measurement to indicate an unbiased downhole drill string measurement.   
     
     
         2 . The method of  claim 1 , wherein the drilling parameters include a hydrostatic pressure of drilling mud about the drill string, a weight of the drilling mud, an inner diameter of one or more tubulars in the drill string, and a true vertical depth of the drilling mud in the drill string. 
     
     
         3 . The method of  claim 1  further comprising:
 continuously determining additional biases of the strain data based on a hydrostatic pressure of drilling mud in the drill string, a weight of the drilling mud in the drill string, an inner diameter of the drill string, and a true vertical depth of the drilling mud in the borehole. 
 
     
     
         4 . The method of  claim 3  further comprising:
 removing the additional biases from additional biased downhole drill string measurements during the drilling of the borehole. 
 
     
     
         5 . The method of  claim 1 , wherein the biased downhole drill string measurement indicates a weight on a drill bit of the drill sting. 
     
     
         6 . The method of  claim 1 , wherein the biased downhole drill string measurement is torque on a drill bit of the drill string. 
     
     
         7 . The method of  claim 1  further comprising:
 causing pressure from drilling fluid to exert force on the drill string; 
 detecting, while holding the drill string weightless, strain from the one or more strain gauges; and 
 determining a relationship between the strain and un-tarred weight on the drill string. 
 
     
     
         8 . The method of  claim 7 , wherein the pressure is hydrostatic pressure or hydrodynamic pressure. 
     
     
         9 . One or more machine-readable mediums including instructions that, when executed by a processor, eliminate bias in strain data produced by one or more strain gauges in a drill string, the instructions comprising:
 instructions to determine, while the drill string is drilling a borehole, a bias in strain data based on drilling parameters detected during the drilling; and   instruction to remove the bias from a biased downhole drill string measurement to indicate an unbiased downhole drill string measurement.   
     
     
         10 . The one or more machine-readable mediums of  claim 9 , wherein the drilling parameters include a hydrostatic pressure of drilling mud about the drill string, a weight of the drilling mud, an inner diameter of one or more tubulars in the drill string, and a true vertical depth of the drilling mud in the drill string. 
     
     
         11 . The one or more machine-readable mediums of  claim 9 , the instructions further comprising:
 instructions to continuously determine additional biases of the strain data based on a hydrostatic pressure of drilling mud in the drill string, a weight of the drilling mud in the drill string, an inner diameter of the drill string, and a true vertical depth of the drilling mud in the borehole.   
     
     
         12 . The one or more machine-readable mediums of  claim 11 , the instructions further comprising:
 instructions to remove the additional biases from additional biased downhole drill string measurements during the drilling of the borehole.   
     
     
         13 . The one or more machine-readable mediums of  claim 9 , wherein the biased downhole drill string measurement indicates a weight on a drill bit of the drill string. 
     
     
         14 . The one or more machine-readable mediums of  claim 9 , wherein the biased downhole drill string measurement is torque on a drill bit of the drill string. 
     
     
         15 . An apparatus comprising:
 a processor;   one or more machine-readable mediums including instructions that, when executed by the processor, eliminate bias in strain data produced by one or more strain gauges in a drill string, the instructions including
 instructions to determine, while the drill string is drilling a borehole, a bias in strain data based on drilling parameters detected during the drilling, and 
 instruction to remove the bias from a biased downhole drill string measurement to indicate an unbiased downhole drill string measurement. 
   
     
     
         16 . The apparatus of  claim 15 , wherein the drilling parameters include a hydrostatic pressure of drilling mud about the drill string, a weight of the drilling mud, an inner diameter of one or more tubulars in the drill string, and a true vertical depth of the drilling mud in the drill string. 
     
     
         17 . The apparatus of  claim 15 , the instructions further comprising:
 instructions to continuously determine additional biases of the strain data based on a hydrostatic pressure of drilling mud in the drill string, a weight of the drilling mud in the drill string, an inner diameter of the drill string, and a true vertical depth of the drilling mud in the borehole.   
     
     
         18 . The apparatus of  claim 17 , the instructions further comprising:
 instructions to remove the additional biases from additional biased downhole drill string measurements during the drilling of the borehole.   
     
     
         19 . The apparatus of  claim 15 , wherein the biased downhole drill string measurement indicates a weight on a drill bit of the drill string. 
     
     
         20 . The apparatus of  claim 15 , wherein the biased downhole drill string measurement is torque on a drill bit of the drill string.