SPE Drilling & Completion
Volume 28, Number 1, March 2013, pp. 93-104

Summary

American Petroleum Institute (API) design equations describing burst and collapse limits of tubulars do not address pipe body response when axial stress in the casing exceeds the material yield strength. However, casing yielding commonly occurs in thermal operations in western Canada, where steam-assisted gravity drainage (SAGD) and cyclic-steam-stimulation (CSS) operating temperatures generally range from 200 to 350°C. Cemented production casing is subject to both passive and active loading conditions during operation: thermally induced strain-based cyclic axial loading occurs in conjunction with net internal or external differential pressure. A sound engineering basis for selecting tubular configurations that considers the combined loading state in this situation and establishes an appropriate design margin does not currently exist. This paper describes numerical analyses for combined post-yield loading conditions and provides a starting point for burst and collapse design for thermal casing. Burst analysis of axially constrained casing indicates that, contrary to what might be inferred from elastic-strength calculations, an initial thermally induced axial compressive strain does not substantially reduce the burst (rupture) pressure. By contrast, even low net external pressures can lead to ovalization and loss of wellbore access when combined with thermally induced axial strain if the cement sheath does not offer adequate radial support. Sensitivity studies demonstrate the strong influence of pipe diameter-to-thickness ratio (D/t) and pressure ratios and pipe material mechanical properties on ovalization response. Analysis results are compared with API burst and collapse predictions, thermal operating experience at Shell Canada's Peace River project, and available physical testing results for similar loading conditions.

© 2013. Society of Petroleum Engineers

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History

• Original manuscript received: 24 August 2012
• Meeting paper published: 6 March 2012
• Revised manuscript received: 12 November 2012
• Manuscript approved: 19 November 2012
• Version of record: 14 March 2013