During the oil production, to monitor the work conditions of an electrical submersible pumping (ESP), an electrical current recorder is used to record the curves of electrical current of the driving motor of an ESP. The current curves are printed by the recorder on recording charts and they indicate various working conditions of an ESP. Subtle malfunction or abnormal problems of the ESP can be detected and further analyzed from various features of these current curves on the recording charts. Presently these current charts are manually read and analyzed in oil fields. In this paper, a diagnosis expert system is presented for automatically analyzing these current recording charts and identifying work condition of an ESP. This expert system includes an open knowledge base, which can be updated or enriched according to the identified features of current curves on the recording charts, and a condition monitoring and failure pattern identification or recognition method, called "pick-up method of recording chart feature", which can be correctly applied in most cases. It has been proved that the developed expert system can effectively improve the accuracy and efficiency of failure diagnosis and work condition monitoring of ESP.
As an effective tool, Electrical submersible pumping (ESP) have been increasingly employed in oil production. ESP is a multistage centrifugal pump, which are driven by art electric motor. The pump and motor are normally suspended from the production tubing, with the motor positioned below the pump, and the pump discharging directly into the production tubing. Power is supplied to the motor through a three-conductor cable, which is run down to the motor from surface through the tubing/casing annulus.
The velocity that is imparted to the fluid by the rotating impeller is converted into pressure energy by the diffuser in a centrifugal pump. Each impeller/diffuser set is called a "stage". The discharge of one stage is the input of the next stage in a multistage pump and hence higher heads can be achieved, which would be impossible with a single impeller. Variable speed drivers (VSDs) change the frequency of the powersupplied to the motor, thus changing the pump speed and operating envelope according to the affinity laws. Since shaft horsepower and motor rating are linearly proportional to frequency, smaller pumps and motors run at a higher frequency can give equivalent performance to the larger equipment at line frequency. An electrical current recorder instrument is installed to monitor and record the electrical current curves of the pump and motor make a daily or weekly recording of the pump and motor. A recording should be made while the well is performing properly, so that comparisons may be made if any fault develops. The recording charts can be used to continuously monitor and diagnose the electrical current of the driving motor of an ESP.
The pick-up method of recording chart feature is a key technique by using a computer to automatically recognize the recording charts. Various features on the recording charts reflectlots of fault of an electrical submersible well system [1, 2].
