Changes in Permeability of Kimachi Sandstone and Iidate Granite with Supercritical CO2 Injection

Abstract

Understanding of interfacial interactions among supercritical CO 2 (scCO 2 ), water, and mineral phase is necessary for a precisely prediction of CO 2 migration into aquifers. The purpose of this study is to assess the impact of scCO 2 on flow property of Kimachi sandstone and Iidate granite in a CO 2 rich dense phase i.e., the condition of which scCO 2 is expected to displace formation water in the course of CO 2 injection. In this experiment, the permeability test for CO 2 gas was conducted before and after a CO 2 saturation procedure that is filled with scCO 2 in pores of rocks. To investigate a mechanical property of rock specimen in the presence of scCO 2 , the axial strain was also measured using a laser displacement sensor during scCO 2 saturation processes.Our results showed that both Kimachi sandstone and Iidate granite samples tested have a more or less decreasing trend of gas permeability with increasing exposure time to scCO 2 . It was further shown that the axial strain of Kimachi sandstone and Iidate granite increased as scCO 2 -exposure time increased.Additionally, increases in masses and dimensions of test samples before and after scCO 2 saturation processes were clearly observed under atmospheric pressure conditions. It can, therefore be said that Kimachi sandstone and Iidate granite could be capable of swelling and permeability change accompanied by CO 2 sorption into their internal structures in the presence of scCO 2 . Furthermore, the observed significant reduction in permeability cannot fully be explained by two model predictions based on Kozeney-Carman equation and Hagen-Poiseuille law, considering CO 2 sorption onto mineral phases.The present results pointed out that CO 2 sorption on rocks under geological CO 2 storage conditions could have a significantly impact on flow property of rocks during CO 2 injection and storage processes.