Shale Swelling, Osmosis, and Acoustic Changes Measured Under Simulated Downhole Condition

Abstract

Preserved shale samples from four different shale cores were exposed to various aqueous fluids while under simulated downhole stress conditions. Before fluid exposure, the samples were not contacted by any aqueous fluid, including simulated pore fluid. Time-dependent measurements of pore pressure, swelling, and acoustic velocities were made. Pore pressures both less than and greater than the applied fluid pressure were observed, and apparent osmotic membrane efficiencies were calculated. Swelling was found to depend not only on the shale type and the fluid but also on the level of confining stress; sufficient confining stress can prevent swelling. Swelling anisotropy was observed. Acoustic velocities were found to change as a result of fluid exposure, but significant velocity decrease occurred only in the presence of chemically induced swelling. S-wave velocities were found to be more sensitive than P-wave velocities. Because swelling is expected to occur mostly in the radial direction around a wellbore and only very close to the wellbore, the best detection method would be either (1) well-parallel S-velocities processed to yield the high-frequency (near-wellbore) slowness or (2) S-velocities measured in the radial direction instead of the well-parallel direction.

Responses of chemically active and naturally fractured shale under time‐dependent mechanical loading and ionic solution exposure

“…For example, Ewy et al presented the complex pore pressure and strain responses during the pressure transmission test on a shale sample with high content of clay. Ewy and Stankovic measured pore pressure and shale swelling under simulated downhole conditions and showed that swelling depended on not only shale type and fluid but also the confining stress. Ewy tested 9 clay‐rich shale samples under humidity control and brine contact and showed the distinct relationships among the saturation, suction, and volume change.…”

On the Effect of CO2 on Seismic and Ultrasonic Properties: A Novel Shale Experiment

“…The difference between synthetic and native pore fluid is, however, assumed to be insignificant with osmotic swelling only playing a minor part in the observed swelling. Moreover, Ewy and Stankovic [86] found that sufficient effective stress prevents chemically induced swelling which is an indication that water adsorption in an undersaturated shale is the main mechanism.…”

Al2O3 and CuO nanoparticles as promising additives to improve the properties of KCl‐polymer mud: An experimental investigation

“…Because of the invasion of water into their pore throats, shale instability occurs, which results in clay swelling and further induces osmosis. [ 6 ] It has been known that shale wellbore instability is induced by the type of drilling mud. [ 7 ] Some investigators believe that potassium chloride (KCl) is the optimum choice for shale drilling due to its chemical effects and time dependency.…”