Yucun Lou

Force generated by a swelling elastomer subject to constraint

When an elastomer imbibes a solvent and swells, a force is generated if the elastomer is constrained by a hard material. The magnitude of the force depends on the geometry of the constraint, as well as on the chemistry of the elastomer and solvent. This paper models an elastomer crosslinked on the exterior surface of a metallic tubing. The elastomer then imbibes a solvent and swells. After the swollen elastomer touches the wall of the borehole, a significant amount of time is needed for the solvent in the elastomer to redistribute, building up the sealing pressure to the state of equilibrium. The sealing pressure and the sealing time are calculated in terms of the geometric parameters (i.e., the thickness of the elastomer and the radii of the tubing and borehole), the number of monomers along each polymer chain of the elastomer, and the affinity between the elastomer and the solvent.

Swellable elastomers under constraint

Swellable elastomers are widely used in the oilfield to seal the flow of downhole fluids. For example, when a crack appears in self-healing cement, the liquid in the surroundings flows into the crack and permeates into the cement, causing small particles of elastomers in the cement to swell, resulting in the blocking of the flow. Elastomers are also used as large components in swellable packers, which can swell and seal zones in the borehole. In these applications, the elastomers swell against the constraint of stiff materials, such as cement, metal, and rock. The pressure generated by the elastomer against the confinement is a key factor that affects the quality of the sealing. This work develops a systematic approach to predict the magnitude of the pressure in such components. Experiments are carried out to determine the stress-stretch curve, free swelling ratio, and confining pressure. The data are interpreted in terms of a modified Flory-Rehner model.

Kinetics of swelling under constraint

Swellable elastomers are used to seal flow channels in oilfield operations. After sealing, the elastomers are constrained triaxially, and a contact load builds up between the elastomers and surrounding rigid materials. For these applications, the ability to predict the evolution of the contact load is important. This work introduces an experimental setup to measure the contact load as a function of time. The experimental data are well represented by a simple time-relaxation equation derived from the linear poroelastic theory, enabling a determination of the effective diffusivity of solvent inside the elastomers.

Elastic Leak for a Better Seal

Elastomeric seals are widely used to block fluids of high pressure. When multiple seals are installed in series and the spaces between the seals contain compressible fluids (e.g., gas or gas–liquid mixture), the seals often damage sequentially, one after another. Here, we demonstrate that the serial seals achieve high sealing capacity if individual seals undergo elastic leak, without material damage. When individual seals leak elastically, fluid fills the spaces between the seals. Instead of damage one after another, all the seals share the load. The elastic leak of individual seals greatly amplifies collective sealing capacity of serial seals.

Crack Tunneling in Cement Sheath of Hydrocarbon Well

In a hydrocarbon well, cement fills the annular gap between two steel casings or between a steel casing and rock formation, forming a sheath that isolates fluids in different zones of the well. For a well as long as several kilometers, the cement sheath covers a large area and inevitably contains small cracks. The cement sheath fails when a small crack grows and tunnels through the length of the well. We calculate the energy release rate at a steady-state tunneling front as a function of the width of the tunnel. So long as the maximum energy release rate is below the fracture energy of the cement, tunnels of any width will not form. This failsafe condition requires no measurement of small cracks, but depends on material properties and loading conditions. We further show that the critical load for tunneling reduces significantly if the cement/casing and cement/formation interfaces slide. [DOI: 10.1115/1.4031649]