Abstract

Elastomer is a widely used seal material in oil and gas wells. Seal components in wellhead and completion equipment are important barrier elements for maintaining well integrity. In general, unlike metallic seals, it is believed that elastomer seal's performance is not highly dependent on its surface characteristics. However, there are some evidences that suggest that elastomer surface quality or defects like wear, blistering, etc. can impact fluid penetration risk and leakage.

The effect of elastomer surface quality on sealability is difficult to investigate using macroscopic (equipment level) finite element models. This paper presents a novel modelling approach that can simulate fluid penetration and predict leakage rates considering surface topography/characteristics of the elastomer sealing interface. The leakage model consists of a contact mechanics model and a fluid flow model. Deterministic contact-mechanics model can take surface topographical measurements as an input and simulate actual contact area, and microscopic gaps at different loads. This contact gap information is then used by the fluid flow model to predict flow path and calculate leakage rates.

To represent elastomer seal surface and apply the developed model, different types of rough surfaces were generated. Various operational, design, and failure scenarios were simulated to investigate the effects of surface characteristics, elastomer material properties, fluid properties, etc. on the elastomer sealability. Preliminary results demonstrate that elastomer surface characteristic such as degree of finishing can have notable influence on the seal quality as measured by contact pressure required to achieve zero leakage rate. As expected, harder elastomer seal material exhibited more sensitivity to surface quality than softer material. High fluid pressure and low viscosity were observed to increase the leakage rates for similar contact pressure distribution.

Finite element modelling based seal design is typically limited to the analysis of contact pressure distribution at the sealing interface. Presented leakage model helps further extend the design workflow by enabling consideration of surface characteristics of the seal. With further refinement and experimental validation, the model could be used to create lookup tables of contact pressures. These values can be used as target for finite element analysis of seal equipment design.

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