Method for calibration of indirectly measured quantities

Abstract

A method for calibrating a system in an oilfield. The method involves operating a component which includes both a direct sensor and an indirect sensor. Additionally, a processing-capable calibration unit in installed on the system and receives signals from the direct sensor and the indirect sensor. After the indirect sensor calculates indirect physical measurements and the direct sensor calculates direct physical measurements, the calibration unit compares the indirect physical measurements with the direct measurements and determines the difference between them. The calibration unit then computes a calibration command and communicates it to the indirect sensor, which uses this command to adjust its future indirect measurements.

1 . A method for calibrating an oilfield system, the method comprising:
 a) operating a component having a direct sensor, an indirect sensor, and a calibration unit wherein said calibration unit includes a processor;   b) determining at least one indirect physical measurement with said indirect sensor;   c) measuring at least one direct physical measurement with said direct sensor;   d) comparing with said calibration unit said at least one indirect physical measurement with said at least one direct physical measurement, and;   e) sending a calibration command from said calibration unit to said indirect sensor.   
     
     
         2 . The sensor calibration method of  claim 1 , further comprising the additional steps of embedding an error limit in said calibration unit and preventing said sending step if the difference between said direct measurement and said indirect measurement exceeds said error limit. 
     
     
         3 . The sensor calibration method of  claim 1  wherein step b) further comprises averaging said at least one indirect physical measurement over a time interval. 
     
     
         4 . The sensor calibration method of  claim 3  wherein step c) further comprises defining said at least one direct physical measurement within said time interval. 
     
     
         5 . The sensor calibration method of  claim 1  wherein said indirect sensor receives said calibration command and adjusts future measurements based on said calibration command. 
     
     
         6 . A dynamic calibration apparatus comprising:
 an indirect sensor wherein said indirect sensor obtains a secondary indirect measurement and converts said secondary indirect measurement into a primary indirect measurement of a quantity;   a direct sensor disposed on said subsystem wherein said direct sensor obtains a direct measurement of said quantity, and;   a calibration device, having a processor, in communication with said direct sensor and said indirect sensor wherein said calibration device communicates a calibration algorithm to correct said indirect sensor.   
     
     
         7 . The dynamic calibration apparatus of  claim 6  wherein said indirect sensor is contained within an instrumented sensor subsystem. 
     
     
         8 . The dynamic calibration apparatus of  claim 6  wherein said calibration device sets an error limit and prevents calibration if the difference between said direct unit and said indirect measurement exceeds said error limit. 
     
     
         9 . The dynamic calibration apparatus of  claim 6  wherein said primary indirect measurement is bounded by a finite time interval. 
     
     
         10 . The dynamic calibration apparatus of  claim 6  wherein said secondary indirect measurement comprises one of power draw on an electric motor and current draw on an electric motor. 
     
     
         11 . The dynamic calibration apparatus of  claim 6  wherein said primary indirect measurement and said direct measurement comprise one of torque, mud flow, and pressure.