Mechanical Testing and Characterization of a Swelling Elastomer

Abstract

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.

Mechanical and structural behavior of a swelling elastomer under compressive loading

“…It can be seen that stress (or pressure) values are higher for 12% salinity as compared to 0.6% (though only marginally), but become almost identical with more swelling. As expected, it is a consistent observation that these elastomers swell more when exposed to lower-salinity brine, since more concentrated solutions would not swell the elastomer as much as the diluted solutions, whether swelling happens due to diffusion or due to osmosis [4]. Under 12% salinity elastomer swells by a lesser amount, and the harder samples need larger stress to deform and fracture.…”

“…However, at the end of the 1-month swelling period, both salinities give almost the same modulus value. Apart from the reasons for fluctuation discussed above [2,4], significant oscillation in K-value may be rationalized from another perspective. During the compression test, sample elastomer disc is compressed in the axial direction, but is free to expand in the radial direction.…”

“…Swelling elastomers swell when they interact with fluids like water or oil [2]. Swelling results in changes in volume, thickness, density, hardness and mechanical properties [3,4]. Swelling rate for a specific elastomer depends on the temperature and composition of the swelling medium.…”

Investigation of Pre- and Post-Swelling Behavior of Elastomeric Material

“…Figure 16 compares stressstrain patterns between the two salinities (0.6% and 12%) after one day and 30 days of swelling. As expected, stress values were higher for 12% salinity as compared to 0.6%, as lower salinities result in higher swelling (softer elastomer), thereby yielding lower stress values (Qamar 2009). At the end of the onemonth swelling period, swelling for both salt concentrations became almost the same; this gives nearly the same fracture loads.…”

“…Material response (volume and thickness swelling, compression set, tensile set, etc.) of an ethylene-propylene diene monomer (EPDM)-type rubber water-swelling elastomer was studied by Qamar (2009;2012a and. Akhtar et al (2012) compared different material models that can be used for simulation studies of swelling elastomers under tensile loading.…”