Experimental validation of core-based pre-stress evaluations in rock: A case study of Yutengping sandstone as CO₂ storage reservoir rock

Yutengping Sandstone is a potential reservoir for geological CO₂ storage in Tieh-chan-shan, Taiwan. Cyclic loadings were applied to rock samples taken from an outcrop to create artificial pre-stress. The accuracies of pre-stress evaluations using two core-based techniques, acoustic emission (AE) and deformation rate analysis (DRA), were investigated under different pre-stresses, delay times, and curing temperatures. The experimental results validate the evaluation of pre-stresses by AE and DRA. Delay time and curing temperature were shown to have minor impacts on the accuracy of these measurements. However, though both axial strain and lateral strain can be used in DRA, the stress memory fades as the delay time increases. Therefore, delay time, which represents the time from the borehole drilling to the DRA test, must be carefully considered when applying these techniques to evaluate the in situ stress of Yutengping sandstone.