Abstract
Elastomeric seals are essential to two great technological advances in oilfields: horizontal drilling and hydraulic fracturing. This paper describes a method to study elastomeric seals by using the pressure-extrusion curve (i.e., the relation between the drop of pressure across a seal and the volume of extrusion of the elastomer). Emphasis is placed on a common mode of failure found in oilfields: leak caused by a crack across the length of a long seal. We obtain an analytical solution of large elastic deformation, which is analogous to the Poiseuille flow of viscous liquids. We further obtain analytical expressions for the energy release rate of a crack and the critical pressure for the onset of its propagation. The theory predicts the pressure-extrusion curve using material parameters (elastic modulus, sliding stress, and fracture energy) and geometric parameters (thickness, length, and precompression). We fabricate seals of various parameters in transparent chambers on a desktop, and watch the seals extrude, slide, rupture and leak. The experimentally measured pressure-extrusion curves agree with theoretical predictions remarkably well.
Highlights
Seals—along with tires, bearings, and medical gloves—are among the most significant applications of elastomers (Gent, 2012)
Emphasis is placed on a common mode of failure found in oilfields: leak caused by a crack across the length of a long seal
We obtain an analytical solution of large elastic deformation, which is analogous to the Poiseuille flow of viscous liquids
Summary
Seals—along with tires, bearings, and medical gloves—are among the most significant applications of elastomers (Gent, 2012). The fluid pressure can cause the elastomer to extrude, which may lead to rupture, loss of contact, or even escape from the sealing site. A crack may form at the end of the seal and cut the extruded material (Fig. 1c) Both modes of damage have been widely observed (Flitney, 2007; Parker, 2007). Fluid can leak through the interface between the elastomer and the wall (Fig. 1d), a mode of failure which we call elastic leak (Liu et al, 2014; Wang et al, 2015). This paper will not discuss elastic leak any further, but will focus on the mode of failure caused by a crack across the length of the seal (Fig. 1b)
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