Probabilistic evaluation of multi-fluid-phase carbon dioxide storage capacities of saline formations in the Pohang Basin, Korea using three-dimensional geologic modeling and grid-based Monte Carlo simulation

Abstract

A series of probabilistic evaluation is performed sequentially using three-dimensional geologic modeling and grid-based Monte Carlo simulation as a linked methodology to estimate multi-fluid-phase (i.e., individual gas-, liquid-, supercritical-, and whole fluid-phase) carbon dioxide (CO2) storage capacities of the target clastic saline formations in the Pohang Basin, Korea. The Pohang Basin is subdivided into the six geologic formations including the two clastic saline formations, which are the sandstone-dominant Fluvial Conglomerate and Sandstone (FCSS) and Shallow Marine Sandstone (SMSS) in ascending order. The results of the three-dimensional geologic modeling show that the six geologic formations are distributed very complicatedly both onshore and offshore with irregular depths and thicknesses, and they are partly dissected and offset by the eight major faults. The two clastic saline formations FCSS and SMSS are deep and thick at the three prospective areas such as Areas 1, 2, and 3 in the modeling domain. The results of the grid-based Monte Carlo simulation show the following three main contents. First, in the two clastic saline formations SMSS and FCSS, CO2 exists as gas, liquid, and supercritical phases with the corresponding distinctive density ranges depending on the pressure and temperature with depth. Second, the theoretical multi-fluid-phase CO2 storage capacities of the SMSS and FCSS all show asymmetric normal distributions. On the other hand, the effective multi-fluid-phase CO2 storage capacities of the saline formations all show log-normal distributions, and their values are much lower than the values of the theoretical multi-fluid-phase CO2 storage capacities. The mean theoretical fluid-phase CO2 storage capacities of the SMSS and FCSS are equal to 2,511.60 Mton and 1,370.91 Mton, respectively. The mean effective fluid-phase CO2 storage capacities of the SMSS and FCSS are equal to 64.19 Mton and 35.32 Mton, respectively. Third, in the SMSS, the grid-wise (elemental) median theoretical and effective multi-fluid-phase CO2 storage capacities are probabilistically higher at Area 1 (mainly as supercritical and liquid phases), intermediate at Area 2 (mainly as liquid and gas phases), and lower at Area 3 (mainly as a gas phase). However, in the FCSS, the grid-wise median theoretical and effective multi-fluid-phase CO2 storage capacities are probabilistically higher at Area 2 (mainly as supercritical and liquid phases), intermediate at Area 1 (mainly as a supercritical phase), and lower at Area 3 (mainly as a gas phase). Finally, four key criteria (parameters) for selecting or ranking the optimal CO2 storage locations are decided by summarizing and analyzing the results of the three-dimensional geologic modeling and grid-based Monte Carlo simulation. On the basis of the four key criteria (parameters), the overall suitability ranks of Areas 1, 2, and 3 for geologic CO2 storage are determined to be the first, second, and third, respectively.