Evaluation of Downhole Electric Components by Monitoring Umbilical Health and Operation

Abstract

A method for monitoring the health of a downhole electrical system including a umbilical cable that connects a downhole electric tool to a power source or controller includes delivering electric signals, such as voltage pulses, to the downhole electric tool, which may be an electric submersible pump. The signals are delivered via the cable from a signal generator and are partially reflected by impedance mismatches in the cable or at other points in the system. Each such partially reflected signal, or response signal, is received by a controller and compared to the delivered electric signals to determine a condition of the power transmission cable.

We claim: 
     
         1 . A method for monitoring a condition of a downhole system, the method comprising:
 delivering an electric signal to a downhole electric device via a downhole power transmission cable from a signal generator;   receiving an electric response signal from the downhole power transmission cable; and   comparing the electric signal to the electric response signal to determine a condition of the downhole power transmission cable,   wherein the electric signal comprises one or more voltage pulses.   
     
     
         2 . The method of  claim 1 , wherein the electric response signal comprises one or more impedance mismatches resulting from a defect in the downhole system. 
     
     
         3 . The method of  claim 2 , further comprising determining the existence and location of the defect based on the electric response signal. 
     
     
         4 . The method of  claim 3 , wherein the defect is selected from the group consisting of a crimp, a kink, fluid intrusion, and insulation damage in the downhole power transmission cable. 
     
     
         5 . The method of  claim 3 , wherein the defect comprises a connector defect. 
     
     
         6 . The method of  claim 3 , wherein downhole electric device comprises a motor, and wherein the defect comprises a defect in the operation of the motor. 
     
     
         7 . The method of  claim 1 , wherein the one or more voltage pulses is a series of voltage pulses. 
     
     
         8 . A method for monitoring the health of a downhole electrical system, the method comprising:
 delivering an electric signal to a downhole electric device via a downhole power transmission cable from a signal generator;   receiving an electric response signal from the downhole power transmission cable; and   comparing the electric signal to the response signal to determine a condition of the downhole power transmission cable,   wherein delivering an electric signal comprises delivering an A/C current signal.   
     
     
         9 . The method of  claim 8 , wherein the electric response signal comprises a signal indicative of a voltage drop between the signal generator and the downhole electric device. 
     
     
         10 . The method of  claim 9 , further comprising monitoring a rate of change of the voltage drop between the signal generator and the downhole electric device. 
     
     
         11 . The method of  claim 8 , wherein the response signal comprises a signal indicative of the change in current between the signal generator and the downhole electric device. 
     
     
         12 . The method of  claim 11 , further comprising monitoring the rate of change of the current between the signal generator and the downhole electric device. 
     
     
         13 . A system for monitoring a downhole cable, the system comprising:
 a controller having a signal generator, a signal receiver, and a signal processor;   a downhole electric device; and   a power transmission cable coupled to the controller and the downhole electric device;   wherein:   the signal generator is operable to generate an electric signal to the downhole electric device via the power transmission cable,   the signal receiver is operable to receive a response signal from the power transmission cable, and   the signal processor is operable to determine a condition of the power transmission cable based on a comparison of the electric signal to the response signal.   
     
     
         14 . The system of  claim 13 , wherein response signal is an impedance mismatch resulting from a defect in the power transmission cable. 
     
     
         15 . The system of  claim 14 , wherein the defect is selected from the group consisting of a crimp, a kink, fluid intrusion, and insulation damage. 
     
     
         16 . The system of  claim 14 , wherein the defect comprises a connector defect. 
     
     
         17 . The system of  claim 14 , wherein downhole electric device comprises a motor, and wherein the defect comprises a defect in the operation of the motor. 
     
     
         18 . The system of  claim 14 , wherein the signal processor is operable to determine the location of the defect based on the impedance mismatch. 
     
     
         19 . The system of  claim 13 , wherein the electric signal comprises a series of voltage pulses. 
     
     
         20 . The system of  claim 13 , wherein the signal processor is operable to determine a source of degradation based on the response signal.