Page 199 - Enhanced Oil Recovery in Shale and Tight Reservoirs

182 Enhanced Oil Recovery in Shale and Tight Reservoirs

Zhang and Sheng (2018) also measured shale (Mancos) strain changes
during water imbibition under isotropic confining pressures. Cylindrical
samples of 38 mm diameter and 76 mm length were used during the shale
swelling experiments. Shale swelling strain was tested. The strain gauges
(1.78 mm width and 3.18 mm length) were cemented to the surface of
the samples to measure strain in axial and lateral directions. A waterproof
silicone rubber (an excellent electrical insulator, even in brine) was used as
a protective coating for the strain gauges and connections. All measurements
were carried out at room temperature, which was kept largely constant and
was recorded for control. The sample with the strain gauge frame was then
placed in a beaker and the core inlet surface was immersed in the distilled
water. The strain was recorded continuously for nearly 2 days until the value
remained constant. The Hoek triaxial cell shown in Fig. 8.8 was used to apply
confining pressure, and an HCM-0032 compression machine (Humboldt
Mfg., Elgin, Illinois) could be used to apply an axial load.
During water imbibition, with the confining pressure increasing from 0 to
20.0 MPa, the radial and the axial swelling strains are shown in Fig. 8.9.
Hydration swelling stress acts as the volume stress to induce plastic swelling
strain (Heidug and Wong, 1996). Although the hydration-induced fractures
experienced a dynamic process of opening and closing locally, the swelling

Figure 8.8 Cutaway view of Hoek triaxial cell.