PRE AND POST-SWELLING MECHANICAL BEHAVIOR OF A WATER-SWELLING ELASTOMER
Swelling elastomers are a very recent development in the world of advanced polymers, and are being successfully used in the form of packers and other sealing elements in various oilfields. Improved design of sealing elements and prediction of seal performance under different well conditions require a good knowledge of mechanical response of the swelling elastomer. This study reports results of hardness and tensile testing carried out on disc and ring samples of a water-swelling elastomer. Material properties of the elastomer were measured before swelling and periodically after swelling for a total testing time of 15 weeks, under water salinities of 0.6%, 12%, and 25%, and temperatures of 25°C, 50°C, 80°C, and 97°C. Reported results can be used by oilfield engineers as prequalification of the elastomer for downhole applications, and by designers using numerical simulations for improvement of elastomer-based sealing and packer design.
Mechanical Testing and Characterization of a Swelling Elastomer
Elastomers are being increasingly used for sealing and other applications in the oil and gas industry. Specifically developed elastomers possess durable properties and have the ability to withstand detrimental effects of heat, chemicals, and harsh environments. For successful modeling and simulation of various downhole processes, it is very important to determine the behavior of elastomer materials under realistic well conditions. Of special interest is the class known as swelling elastomers. This article reports some results from experiments conducted on mechanical testing and characterization of an inert (nonswelling) and a water-swelling elastomer (both belonging to the EPDM family) used for sealing purposes by a local petroleum development firm. Experiments were designed and conducted in accordance with standard ASTM test methods. Apart from regularly available testing equipment, some simple test rigs and fixtures were designed and fabricated. Elastomer behavior was tested for hardness, compression set (at different temperatures and for different periods of time), tensile set (for different periods of time), tensile properties (fracture strength and percent elongation), and swelling. In the swelling test, different sample geometries (unconfined samples and samples mounted on steel plate) were tested for a total duration of 1000 h (roughly 45 days) in salt solutions of different concentrations and at different temperatures. Results show that compression set increases with increasing temperature and testing time, while room temperature tensile set also increases with longer testing time. Compared to the inert elastomer (exhibiting nonlinear elastic behavior like normal rubbers), swelling elastomer surprisingly showed linear stress—strain response. As expected, the inert elastomer did not exhibit any change in volume, while the swelling elastomer showed significant volume/thickness increase with increasing test temperature and decreasing salt concentration.
EFFECTS OF CROSSLINK CHARACTERISTICS ON DENSITY AND SWELLING BEHAVIOUR OF EXPANDED NATURAL RUBBER VULCANISATES
Expanded natural rubber was vulcanised using different techniques to obtain various types of crosslinking including flexible and rigid sulphur and peroxide linkages. Stress-strain measurement based on the Mooney-Rivlin equation was utilised to determine overall crosslink density of the rubber. The expanded NR vulcanisates produced were then characterised with respect to the apparent density and swelling behaviour, these properties being found to be dependent not only on the degree of crosslinking, but also on the type of chemical structure of the crosslink. This was also a suggestion that swelling behaviour was related to apparent foam density.