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.

A computational micromechanics study of stress-assisted martensitic transformation using finite elements is carried out within a thermomechanical framework including the aspect of plastic deformation. The phase transformation is treated by a stress-free transformation tensor corresponding to a certain habit plane variant involving a shape change resulting from shear and dilatational deformations which are eigenstrains within the emerging martensitic phase. General plane strain and axisymmetric analyses are carried out introducing different micromechanical models with appropriate boundary conditions required for the microfield approach. The introduced models are compared with a micromechanical model developed by Tvergaard in the viewpoint of thermodynamic aspects concerning the formation of martensite. The representative volume elements are specified with respect to the Schmid factor for the transformation shear corresponding to an average crystallographic orientation of a grain. We examine elastic-plastic deformations and distribution of transformation-induced microstress fields in both the parent and the emerging product phase due to accommodation of the transformation shape change. Analytical results for the linear elastic case based upon the Eshelby approach will be compared with numerical results. The plastic behavior of austenitic and martensitic microconstituents is described in the context of J2-flow theory with isotropic hardening. The thermomechanical framework is based on an explicit form of a potential suggesting the form of Gibbs free energy, from which transformation conditions on the mesodomain-, interface- and nucleation-site level are derived. The arrangement of martensitic microregions transforming in a stress field is studied considering the thermomechanical coupling of orientation and accommodation effects.

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