Experimental study of the effects of sub- and super-critical CO 2 saturation on the mechanical characteristics of organic-rich shales

Micro- and Macroscale Consequences of Interactions between CO2 and Shale Rocks

“…A gradual decrease in the Young's modulus was measured within 30 days of exposure to both sub-and supercritical CO 2 [169]. The results show that after 10 days of exposure, both the UCS and Young's modulus decreased when CO 2 -saturation pressure increased from 0 to approximately 12 MPa and then started to increase at a saturation pressure from 12 to 16 MPa [167]. However, when the dry shale samples were exposed to scCO 2 for 2 weeks, the Young's modulus and Poisson's ratio were hardly affected.…”

“…CO 2 -brine-caprock interactions can therefore cause changes in the mechanical properties of rocks, in terms of their strength, stiffness, and fracture thresholds, which can increase the risk of CO 2 leaking from the reservoir [163][164][165]. These effects have been experimentally investigated on various shale formations and under different exposure conditions in terms of temperature and pressure [24,70,72,[166][167][168][169][170][171][172][173][174]. The investigated parameters affected by CO 2 exposure include volume change (swelling), strength, stiffness, Poisson's ratio, stress thresholds for crack initiation, and crack damage, as well as the brittleness index.…”

“…During the unconfined compressive strength (UCS) tests, the samples were equipped with acoustic emission sensors to record crack initiation and propagation. The signals from the sensors (of ultrasonic frequency) were correlated with the stress state to provide stress thresholds for crack initiation and damage [72,[166][167][168]. The results are presented in Table 2 for different solutions of CO2 The normalization is done by dividing the value at a given time by the initial value (without CO 2 ).…”

“…For a given exposure fluid under constant temperature and pressure, the stress thresholds for crack initiation and crack damage decrease with the exposure time [72]. For a given exposure time, Yin et al [167] showed that the stress for crack initiation and crack damage decrease with increasing pressure up to 12 MPa and then increase for pressures above 12 MPa. However, the stress thresholds for crack initiation and damage show a decreasing trend with pressure (between 6 and 12 MPa) when exposed to CO 2 or CO 2 -brine [168].…”

A Damage Constitutive Model for the Effects of CO2-Brine-Rock Interactions on the Brittleness of a Low-Clay Shale

“…Therefore, the investigation of shale's mechanical properties after fluidrock interactions is very important for drilling and fracturing industry. Many scholars have done a brilliant research about the variation of shale's strength and Young's modulus after the adsorption of fluids, such as water [16,17], saline solutions [18,19], CO 2 [20][21][22], CO 2 -dissolved water [11], and CO 2 -dissolved brine [23,24]. However, the studies of the brittleness of shale after fluid saturation are limited.…”