Summary
Casing connections in thermal wells experience extreme loads owing to
exposure to high temperatures ranging as high as 200 to 350°C, stresses
exceeding the elastic limit, and cyclic plastic deformation. To date, no
standard procedure has been adopted by the industry to qualify casing
connections for such conditions. In particular, the existing evaluation
standard International Organization for Standardization (ISO) 13679/API 5C5
(ISO 2002) does not apply to tubular loads beyond pipe body yield and
temperatures above 180°C. Proprietary procedures have been used to qualify
connections for individual thermal operations, but none of those has been
accepted as an industry standard.
This paper introduces a new protocol for evaluating casing connections for
thermal applications: Thermal Well Casing Connection Evaluation Protocol
(TWCCEP). While founded on long-standing work in the thermal-well arena, TWCCEP
was developed through a multiclient project sponsored by several major
operators and connection manufacturers. Following project completion, TWCCEP
was released to the public domain and submitted to ISO for adoption as an
international standard.
TWCCEP uses both analytical and experimental procedures to assess
performance of a candidate connection under conditions typical of service in
thermally stimulated wells. The objective of the analytical component is to
assess sensitivities of the candidate connection to selected design variables,
and identify worst-case combinations of those variables for configuration of
specimens for physical testing. The purpose of the physical testing is to
verify performance of the connection specimens under assembly-and-loading
conditions simulating thermal-well service.
In addition to an overview of TWCCEP, this paper illustrates how engineering
analysis, numerical simulation, and reduced-scale physical testing were used to
examine the impacts of various design and loading variables on connection
strength and sealability, and subsequently to formulate the analysis-and-test
matrix prescribed in the TWCCEP evaluation procedure.
Adoption and consistent use of TWCCEP is expected to increase operational
reliability and decrease failure potential of casing strings in thermal wells.
Learnings from the protocol development process will also help in the
formulation of guidelines for connection requalification for thermal
applications, in cases when one or more of the design variables change.
© 2011. Society of Petroleum Engineers
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History
- Original manuscript received:
4 December 2008
- Meeting paper published:
18 March 2008
- Revised manuscript received:
2 April 2011
- Manuscript approved:
26 April 2011
- Published online:
6 September 2011
- Version of record:
15 September 2011
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