Mechanical Problems Case History 2 Pump Wear Electric Submersible Pump (ESP) used for Artificial Lift in Oil Extraction Test Objective To ascertain whether a purely mechanical problem such as pump wear can show a clear change in the current spectrum and that MCSA is a viable CM method for ESPs.
Nameplate details 2 (of) 3Phase, SCIM's (2 x 210 h.p. / 2 x 157kW motors), 60Hz, 2pole. The ESP was operating at a depth of 7500 feet ( 2286 m) in a well deviation of 45°.
Additional Information Special Electrical Submersible Pumps (ESPs) are used worldwide to provide artificial lift in oil wells. They can operate at depths up to 12000 feet (3567 m) at temperatures and pressures of 302 °F (150 °C) and 4000 p.s.i. (27 Mpa). This can result in relatively short run times compared to conventional motorpump drives. The cost of a replacement in the offshore environment is very costly hence online monitoring to get an assessment of the unit's health is very desirable. Outages can be planned and pumping uptake can be redirected to other pumps to avoid a sudden failure of the faulty one (e.g. operate it on reduced load). The use of vibration monitoring is not practical due to the operating environment, depths at which the ESPs operate, etc. MCSA is much more applicable since the measurements can be taken topside.
The difference (red) envelope between the two spectra taken at different times is shown in Figure p5. Note that the magnitude of the 60 Hz component did not change since the motor was operating on fullload in both cases. This change occurred over a period of 4 months. There must be disturbances in the motorpump rotor since there are new components induced around 60 Hz.
Figure p5 Superimposed current spectra showing difference due to worn pump
The pumping process was not being performed efficiently and the unit was removed for inspection and overhaul.
Figure (p6) shows a photo of the faulty pump. There was radial wear on the pump stage hubs and there was also shaft/bushing wear. The result shows there is potential for MCSA to be used for monitoring the health of ESPs.
Figure p6 Radial wear on Stage Hubs shaft bearing wear
Trending of the current spectrum should be used to assess mechanical wear deterioration in the pump.
Expert Comment Trending of the current spectrum should be used to assess mechanical wear deterioration in the pump. BACK to Home Page
Telephone: +44 (0)19755 62446 Click here to contact us
EM Diagnostics Ltd, 20 Greystone Road, Alford, Aberdeenshire, AB33 8TY Scotland, UK
© Copyright E.M. Diagnostics Ltd., 2003 Email:
[email protected]
