In-Situ System Calibration

Abstract

A method for re-calibrating installed downhole sensors used in hydrocarbon wells by the application of a calibration string inserted in the wells and deployed in close proximity to the installed downhole sensor.

I claim: 
     
         1 . A downhole in-situ recalibration device for use in re-calibrating an installed downhole seismic sensor comprising:
 a. a downhole calibration string associated with seismic sensing;   b. wherein said calibration string contains a vibration source used to apply a characteristic seismic signature on one or several downhole points in close proximity to said installed downhole seismic sensor.   
     
     
         2 . The downhole in-situ recalibration device for use in re-calibrating an installed downhole seismic sensor of  claim 1  wherein the installed downhole seismic sensor is coupled to the outside of a well casing and the downhole calibration string is inserted into the wellbore. 
     
     
         3 . The downhole in-situ recalibration device for use in re-calibrating an installed downhole seismic sensor of  claim 1  wherein the downhole calibration string is mechanically coupled to the wellbore casing or tubing after insertion into the wellbore. 
     
     
         4 . The downhole in-situ recalibration device for use in re-calibrating an installed downhole seismic sensor of  claim 3  wherein the calibration string is mechanically coupled to the wellbore casing or tubing by locking arms pressed against the casing or tubing of the wellbore. 
     
     
         5 . The downhole in-situ recalibration device for use in re-calibrating an installed downhole seismic sensor of  claim 3  wherein the calibration string is mechanically coupled by use of a mechanical packer. 
     
     
         6 . The downhole in-situ recalibration device for use in re-calibrating an installed downhole seismic sensor of  claim 3  wherein the calibration string is mechanically coupled by a bow-spring device that expands to mechanically couple the calibration string to the wellbore. 
     
     
         7 . The downhole in-situ recalibration device for use in re-calibrating an installed downhole seismic sensor of  claim 1  wherein the characteristic seismic signature of the calibration string has a known orientation. 
     
     
         8 . A method for in-situ recalibration of an installed seismic sensor in a downhole sensing system in hydrocarbon wells comprising:
 a. Inserting a calibration string associated with seismic sensing in the wellbore of the hydrocarbon well in close proximity to said installed seismic sensor; wherein the calibration string contains a vibration source that can be used to apply a characteristic seismic signature on one or more downhole points in close proximity to said installed downhole seismic sensor;   b. mechanically coupling the calibration string to the wellbore;   c. using the calibration string to apply characteristic signatures at the one or more downhole points that are used to re-calibrate the installed seismic sensor.   
     
     
         9 . The method for in-situ recalibration of an installed seismic sensor in a downhole sensing system in hydrocarbon wells of  claim 8  wherein the calibration string is mechanically coupled to the wellbore casing or tubing by locking arms pressed against the casing or tubing of the wellbore. 
     
     
         10 . The method for in-situ recalibration of an installed seismic sensor in a downhole sensing system in hydrocarbon wells of  claim 8  wherein the calibration string is mechanically coupled to the wellbore casing or tubing by use of a mechanical packer. 
     
     
         11 . The method for in-situ recalibration of an installed seismic sensor in a downhole sensing system in hydrocarbon wells of  claim 8  wherein the calibration string is mechanically coupled to the wellbore casing or tubing by a bow-spring device that expands to mechanically couple the calibration string to the wellbore. 
     
     
         12 . The method for in-situ recalibration of an installed seismic sensor in a downhole sensing system in hydrocarbon wells of  claim 8  wherein the characteristic seismic signature of the calibration string has a known orientation.