Abstract
Abstract Leakage resistance of casing connections can be evaluated by extremely expensive testing procedures. Although testing is required for connection validation, significant amount of resources can be saved by complementing testing with Finite Element (FE) analysis. In this regard, a broadly accepted criterion to characterize leaks in FE simulation is still required. This paper proposes an objective and accurate criterion to characterize leakage resistance of casing connections in axisymmetric FE simulation. The criterion is based on stab flank contact pressures and stab flank engaged length parameters. The criterion is tested in application to API 8 Round LTC connections (5 ½ J55 14lb/ft), and confronted with test results. Leakage envelopes are obtained considering make-up torque and tensile axial loads. The influence of taper on connection sealability is also investigated. The long term goal of the investigation is to derive probabilistic leakage envelopes of casing connections considering manufacturing tolerances, effect of thermal cycles, and seal ovalization due to bending during assembly.
Highlights
Failure of casing and tubing of underground wells has the potential to produce severe environmental damage and huge economic loss
A Finite Element (FE) analysis methodology and a leak criterion were proposed for estimation of leakage resistance envelopes of API 8 Round LTC connections
The analysis considers effects of make-up torque and tensile axial loading, which must be applied in this order
Summary
Failure of casing and tubing of underground wells has the potential to produce severe environmental damage and huge economic loss. Field failures of casing and tubing are most often related to connections, rather than to pipe body. Proper modelling of connection strength and leak resistance is fundamental for safe well operation. There is a recent trend for reliability-based design of wells and well casing, in particular under HTHP (High Temperature High Pressure) conditions [30,31,32,33]. Probabilistic models of pipe body burst and collapse strengths have been significantly studied, as reported in [34]. Well casing reliability cannot be achieved unless probabilistic envelopes of connection resistance are developed [35], in view of the impact of connection failures in the field. Results presented are part of a long-term goal to develop probabilistic leakage
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