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

Abstract

Carbon capture and storage (CCS) by geological sequestration comprises a permeable formation (reservoir) for CO2 storage topped by an impermeable formation (caprock). Time-lapse (4D) seismic is used to map CO2 movement in the subsurface: CO2 migration into the caprock might change its properties and thus impact its integrity. Simultaneous forced-oscillation and pulse-transmission measurements are combined to quantify Young’s modulus and Poisson’s ratio as well as P- and S-wave velocity changes in the absence and in the presence of CO2 at constant seismic and ultrasonic frequencies. This combination is the laboratory proxy to 4D seismic because rock properties are monitored over time. It also improves the understanding of frequency-dependent (dispersive) properties needed for comparing in-situ and laboratory measurements. To verify our method, Draupne Shale is monitored during three consecutive fluid exposure phases. This shale appears to be resilient to CO2 exposure as its integrity is neither compromised by notable Young’s modulus and Poisson’s ratio nor P- and S-wave velocity changes. No significant changes in Young’s modulus and Poisson’s ratio seismic dispersion are observed. This absence of notable changes in rock properties is attributed to Draupne being a calcite-poor shale resilient to acidic CO2-bearing brine that may be a suitable candidate for CCS.

Homogenization of Porous Thin Layers With Internal Stratification for the Estimation of Seismic Reflection Coefficients

“…The considered pressure and temperature conditions are within the range of the reservoir conditions of the Utsira sandstone (e.g., Chadwick et al., 2012; Zweigel et al., 2004). The rock physical properties of the thin layer beds B1 and B2 emulate those of the Utsira sandstone (e.g., Boait et al., 2012; Rabben & Ursin, 2011; Rubino et al., 2011), while of the background resemble those of a shale caprock (e.g., Rørheim et al., 2021). We remark that, for the homogenization procedure, the background is treated as a poroelastic medium.…”

On Frequency-Dependent Rock Experiments: A Comparative Review

“…-Imaging fluid-solid interactions with time is especially enticing for Carbon Capture and Storage (CCS) purposes (as a natural extension to Rørheim et al [189]). • Multi-element PZT transducers could also excite torsional and flexural modes as well as mitigate any potential misalignments by redistributing the stress field.…”

“…Be the fact that C sat 44 < C dry 44 and C sat 66 < C dry 66 as it may, the non-linearity is questioned (only applies to C 44 and C 66 at 9% RH). Rørheim et al [189] performed FO measurements as functions of frequency as well as time on a CO 2 -exposed Draupne specimen where E V and ν VH insignificantly changed over 575 hours. Neither PT measured V P0 nor V S0 significantly changed perhaps due to Draupne's low calcite content.…”

Effect of Field Caprock Shale Exposure to CO2 on Its Mechanical Properties—A Comparison of Experimental Techniques

“…Another non-destructive method uses the low-frequency technique, whereby smallamplitude cyclic axial strains are applied to the investigated specimen at seismic frequency, allowing a direct measurement of stiffness [16]. Long exposure, with a change of fluid from brine to CO 2 , allowed small changes in stiffness to be quantified, thanks to the many repeated cycles of non-destructive testing.…”