Integrity of high-temperature post-yield (HTPY) wells demands use of casing connections that demonstrate suitable structural strength, sealability and galling resistance. Since 2010, Thermal Well Casing Connection Evaluation Protocol (TWCCEP, published as ISO 12835) has been used by operators and connection manufacturers to assess connection performance under representative field conditions. While technically rigorous, TWCCEP programs are costly and time-consuming, and full-scope TWCCEP evaluations on multiple size/weight/material combinations are challenging to achieve.
This paper describes a product line evaluation (PLE) approach that enables effective qualification of several members of a connection family for HTPY applications with substantial savings of effort, cost and time. Some PLE strategies were used in the past for conventional stress-based-design applications, but not for strain-based-design applications – until recently, when a new HTPY PLE approach was proposed via an industry-sponsored project. This new HTPY PLE method relies on existence of a Reference Connection that has been qualified with a prior evaluation and/or field use. Another member of the same family (Candidate Connection) is then qualified based on existing data for the Reference Connection, and comparative evaluations of the Reference and Candidate Connections.
The paper illustrates basic HTPY PLE concepts, and analytical-experimental tools and processes used for the comparative evaluations. The HTPY PLE method incorporates several assessment steps, which PLE users select according to their field application severity, risk tolerance, and desired level of confidence in the assessment results. The paper emphasizes significance of design and manufacturing variables that are relevant for the HTPY PLE method, some of which are not commonly monitored by connection users – such as circumferential non-uniformity (seal waviness). In a case study example, the paper shows how the HTPY PLE can be used to qualify a connection needed for an optimized well completion, and the resultant cost-time savings. Upon validation, the HTPY PLE method is expected to enhance effectiveness of thermal well integrity and reduce connection failure potential.