Analysis of shale property changes after geochemical interaction under CO2 sequestration conditions

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

“…Lebedev et al [35] considered anisotropy for their shaley sandstones that also decreased in P-wave velocity upon scCO 2 injection into brine-occupied pore space. Consistent with their compressive and tensile strength results, Choi et al [25] measured increasing P-wave velocity if only exposed to scCO 2 . Dewhurst et al [18] reiterated that shale dehydration may alter the rock properties being measured: strength and elastic properties (Young's modulus and Poisson's ratio) from triaxial testing are particularly impacted by pore fluid loss.…”

“…Uniaxial compressive strength (UCS) experiments on shales exposed to CO 2 -water or CO 2 -brine feature a reduction of Young's modulus E and Poisson's ratio ν [16,[20][21][22][23][24][25]. If only exposed to scCO 2 , Choi et al [25] measured an increased Young's modulus.…”

“…Uniaxial compressive strength (UCS) experiments on shales exposed to CO 2 -water or CO 2 -brine feature a reduction of Young's modulus E and Poisson's ratio ν [16,[20][21][22][23][24][25]. If only exposed to scCO 2 , Choi et al [25] measured an increased Young's modulus. Tensile strength is determined by the Brazilian test, in which different shales were found to be both sensitive (decrease and increase in strength) [25][26][27][28][29] and insensitive (constant strength) [30] to CO 2 exposure.…”

“…If only exposed to scCO 2 , Choi et al [25] measured an increased Young's modulus. Tensile strength is determined by the Brazilian test, in which different shales were found to be both sensitive (decrease and increase in strength) [25][26][27][28][29] and insensitive (constant strength) [30] to CO 2 exposure. The common denominator in both experiment types is that the specimens are submitted to mechanical testing at ambient temperature and pressure conditions after being exposed to CO 2 .…”

“…Their results are however inconclusive due to procedural flaws related to limited number of measurements that made statistical analysis difficult, and CO 2 exsolution that could affect the undrained bulk modulus via pore fluid compressibility caused by decreasing pore pressure during loading. Choi et al [25], Al-Ameri et al [33], Elwegaa et al [34] measured decreasing ultrasonic P-and S-wave velocities post-CO 2 exposure which the two latter converted to decreasing dynamic Young's modulus assuming isotropy. Lebedev et al [35] considered anisotropy for their shaley sandstones that also decreased in P-wave velocity upon scCO 2 injection into brine-occupied pore space.…”