Evaluating Pressure Integrity of Polymer Ring Seals for Threaded Connections inHP/HT Wells and Expandable Casing

摘要

This paper presents new technology for evaluating highpressuregas seal integrity of polymer ring seals used assecondary or backup pressure seals in casing and tubingthreaded connections. This new technology may also enablethe further consideration of API connections with ring seals,as an alternative to premium connections, for appropriateapplications. A nonlinear elasto-viscoplastic constitutivemodel for the behavior of polymers and elastomers has beendeveloped and extended to the specific application of analysisof casing and tubing connections with fiberglass-filled PTFEring seals. Procedures for modeling makeup of a connectionincluding a fiberglass-filled PTFE ring seal have beendeveloped using a finite element model of 10-3/4-inch OD,45.5 lb/ft, P-110 API Buttress Thread Casing with a Seal RingGroove. The results of finite element analysis of makeup,followed by the application of thermal, axial and internalpressure loads are presented in this paper. In addition, basedon the interest in the development of gas-tight threadedconnections for expandable casing, the finite element modelwas subjected to a radial expansion of a 20 percent increase inthe outside diameter. In this paper, the theory of theconstitutive model is summarized and calibration of the modelwith experimental test and published data are presented. Thefocus of the finite element analysis results is on the contactpressures between the ring seal, coupling groove andpin threads.