Fig. 1 Schematic of sealing in oil and gas wells

Fig. 2 The relation between the volume fractions in hydrating cement and the degree of hydration[22]

Fig. 3 The evolution of mechanical properties with the degree of hydration[30]

Fig. 4 (a) The pore pressure, (b) effective hoop stress and (c) effective radial stress are plotted as functions of the degree of hydration. The solid lines are for stiff formation (40 GPa); dashed lines are for soft formation (5 GPa)[22]

Fig. 5 The cross-section of a well[32]

Fig. 6 The hoop stress in the cement sheath under inner pressure

Fig. 7 The thermal stress in the cement sheath

Fig. 8 The failure modes of cement sheath

Fig. 9 The opening profile of a tensile crack[32]

Fig. 10 Schematic of a tunneling crack in the cement sheath[32]

Fig. 11 (a) The normalized energy release rate as a function of the normalized width of the tunnel, (b) failsafe diagram in the plane with axes of the normalized Young's modulus and normalized fracture energy of the cement[32]

Fig. 12 Schematic of disk crack extension

Fig. 13 The effect of interfacial sliding on the energy release rate of tunneling crack[32]

Fig. 14 The correlation between the fracture energy and elastic modulus of cement and its effect on the integrity of cement sheath[32]

Fig. 15 Schematic of the structures and work principles of elastomeric seals

Fig. 16 Full scale test on the swellable packers[45]

Fig. 17 Two failure modes of mini swellable packers[46]

Fig. 18 Transparent desktop setup, and two failure modes observed by using this setup[47-48]

Fig. 19 Failure modes of elastomeric seals[48]

Fig. 20 Swelling process of elastomer in a swellable packer under plane strain condition[73]

Fig. 21 The distribution of contact pressure along the length of a packer[76]

Fig. 22 The extrusion and sliding of a piece of precompressed elastomer under fluid pressure[48]

Fig. 23 Fluid pressure extrusion relationship

Fig. 24 (a) Comparison between the theoretical prediction and experimental measurement on $p-Q$ relation; (b) The deformation and fracture of a hydrogel sample[48]

Fig. 25 Fracture model of an elastomeric seal[48]

Fig. 26 The relations between leak pressures and geometrical parameters. Solid dots are experimental results, purple lines are theoretical predictions[48]

Fig. 27 Schematics of (a)$\sim$(c) classical sealing theory and (d)$\sim$(f) elastic leak

Fig. 28 Experimental results of elastic leak

Fig. 29 Effects of geometric parameters on the leak pressure[47]

Fig. 30 Principle of spaced packers

Fig. 31 Instability formed in the swelling of an elastomeric packer[46]

Fig. 32 Instability in elastic leak