EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Mechanical properties of shale following saturation with CO2 and CO2-based fluids: experimental and modeling study

Bingbin Xie, Qiao Lyu, Jingqiang Tan, and David Wood
Bingbin Xie et al.

Impacts of saturation with CO2 and CO2-based liquids are vital for understanding shale's mechanical properties associated with supercritical-CO2 optimized shale gas extraction and geological capture and storage of CO2 in shale reservoirs. A sequence of triaxial compression tests is performed to examine the impact of subcritical CO2, supercritical CO2, subcritical CO2-water, supercritical CO2-water, subcritical CO2-NaCl, and supercritical CO2-NaCl saturation on shale strength. A statistical damage constitutive model of shale after CO2, CO2-water, and CO2-NaCl saturation is established to describe shale's stress-strain relationships under various immersion conditions.

The laboratory findings indicate that the change of the axial stress, Young's modulus, and axial strain of shale after immersion verifies the physical and chemical reactions that occur between shale and the soaking fluids. Mechanical properties of shale show the greatest variations after CO2-water saturation. The variation in mechanical properties of shale after CO2-NaCl saturation is smaller than those of shale under CO2-water saturation owing to the precipitation of NaCl crystals. Pure CO2 saturation has the smallest influence on shale's mechanical properties among the three types of liquids assessed. CO2 in a supercritical state shows a stronger impact on shale than the subcritical state for the same sort of fluids. Also, following saturation, all the shales display a mixed tensile-shear failure mode. The cohesion force of shale increments following pure CO2 saturation, whereas it diminishes following CO2-water and CO2-NaCl saturation. Decreases in the internal friction angles are observed for all the soaked shales. The anisotropy of shale leads to a slight difference between the actual failure angle and the failure angle measured by the Mohr-Coulomb criterion.

The stress-strain relationship of shale under different confining pressures is effectively described by the Weibull probability distribution and the principle of strain equivalence. This establishes statistical damage constitutive equations of shale under different soaking conditions. The values of key modeling parameters, including F0 and m, are highly dependent on the brittleness and strength of shale associated with various soaking conditions.

How to cite: Xie, B., Lyu, Q., Tan, J., and Wood, D.: Mechanical properties of shale following saturation with CO2 and CO2-based fluids: experimental and modeling study, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13143,, 2022.