Schlumberger

Technical Paper: Use of Failure Analysis Techniques to Improve Reliability by Material Selection in SAGD Applications

Society: SPE
Paper Number: 20110427
Presentation Date: 2011
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Abstract

Schlumberger Artificial Lift has developed a new electrical submersible pump (ESP) system for operation at 250ºC [482ºF]. In late 2009, the system has gone through a benchmark test jointly launched by Schlumberger and ConocoPhillips, successfully validating the temperature limit. During the post-test evaluation, axial cracks were found in ceramic sleeves in the pump. Although cracks did not translate into system failure, it was noted as a cause of concern as it may affect the long-term system reliability.

In this work, defect investigation and failure analysis were performed, combined with Finite Element Analysis (FEA) simulation and experimental verification to reproduce and predict the failure mode. A numerical model was developed on the basis of Theoretical Elasticity and showed that the aforementioned failure mode is the result of axial thermal stress caused by difference in the coefficient of thermal expansion (CTE) of components in the shaft string coupled with the pump construction.

Experiments were conducted on a pump with the same construction type and the failure mode was successfully replicated. By fitting the experimental crack-temperature to the numerical simulation, the model is able to predict the failure mode in ceramic sleeves. The validated numerical model was used to screen suitable alloys for key components in the shaft string to reduce the thermal stress. A special alloy was identified and experimentally verified to increase the crack-temperature up to 280ºC [536ºF].

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