Critical pore pressure assessment for CO2 geological storage in Gyeongsang Basin, Korea, from a geomechanics perspective

We use a relatively simple analytic model incorporating two primary geomechanical factors–in situ stress and frictional coefficient of discontinuity–to assess the critical pore pressure increase associated with CO 2 geological storage that initiates shear activation of pre-existing fractures and faults. Shear activation of fractures/faults can break the sealing integrity along the discontinuities, providing possible CO 2 leakage channels. With an example of Gyeongsang Basin, Korea, which is considered a potential onshore geological storage site, the available in situ stress measurement data are analyzed to infer the stress states at an assumed storage depth of 1 km. The stress magnitudes in the basin are characterized by their spatial heterogeneity, implying that the critical pore pressure may vary depending on locations. As another primary factor for the analysis, frictional coefficient is shown to be possibly correlated with clay content in the host rocks encompassing the discontinuities, and in the infillings within the discontinuities, which demonstrates the possibility of estimating the frictional property from the clay content measurable using borehole geophysical logs. Based on the in situ stress conditions coupled with pore pressure change and assumed frictional coefficient of 0.6, the critical pore pressure is estimated, which would induce shear activation along well-orientated discontinuities for slip under the given stress states and consequently provide potential CO 2 leakage pathways. The estimated critical pore pressure as an upper bound of allowable pore pressure is 4–8 MPa above the hydrostatic pore pressure in most of the basin, whereas the same is 0–4 MPa in the southern part of the basin. These results may be useful in the site selection stage for CO 2 geological storage project.