Measurement of the scCO2 Storage Amount and Physical Property Changes of the Janggi Sandstone after the CO2 Injection

Abstract

Measurement of the scCO2 Storage Amount and Physical Property Changes of the Janggi Sandstone after the CO2 Injection

Seyoon Kim

Department of Earth Environmental Sciences, Graduate School, Pukyong National University, Republic of Korea

Abstract

The amount of scCO2 stored in the reservoir rock after the scCO2 injection was very important factor to determine the optimal CO2 storage site. The laboratory experiments were performed to measure the amount of scCO2, replacing water in pore spaces of the Janggi sandstone, which was considered one of the most available CO2 storage rocks in Korea. And the scCO2 storage ratio (referred from the portion of scCO2 volume vs. water volume in pore spaces of the reservoir rock after the scCO2 injection) and the maximum scCO2 storage capacity for the Janggi sandstone layer were also calculated. To measure the amount of scCO2 stored in the Janggi sandstone after the injection, the sandstone core was dried at 50 ℃ in an oven and its dry mass was weighed. The dried core was immerged in water for 3 days to fill in the pore spaces of the core and then it was fixed in the high pressurized cell. Water was flushed through the core at 10 bar of the injection pressure for 3 pore volumes of the core to fully saturate the micro pores with water. Then, the end of the effluent of the cell was closed by the valve and the pore water in the cell was pressurized upto 100 bar at 50 ℃ to simulate CO2 storage condition under the sub-surface. The scCO2 was injected into the influent of the cell to replace water in the pore spaces of the core at 110 bar until the pressure of the pore water in the core reach to 110 bar from 100 bar. After more than 3 pore volumes of scCO2 was flushed out form the core (the replacement of scCO2 was successfully done), the core mass was weighed again to measure the amount of water replaced by scCO2 in the sandstone core. Then the scCO2 storage ratio was calculated as the fraction of scCO2 volume in the total pore space of the core. From the experiment, the scCO2 storage ratio of the Janggi sandstone was calculated as 16.98 %, which can be used to estimate the maximum CO2 storage capacity for the Janggi sandstone layer. Assuming that the CO2 storage site is 1,000 m in length, 500 m in width and 15 m in average thickness of the sandstone layer under 800 m in depth (from sata of the drilling profile and the geostructural survey), the maximum CO2 storage capacity for the Janggi sandstone layer is about 96,000 ton, investigating that the Janggi sandstone layer have a great possibility for CO2 storage testing site in Korea. Physical property change of reservoir rock by CO2 injection is one of the important factors to evaluate the CO2 leakage safety. For the experiment to measure physical property changes of the Janggi sandstone, 4 sandstone cores acquired at the Janggi basin and groundwater sampled at the thermal spring near the drilling site were used. Four sandstones were located in 5 L capacity of the high pressurized cell in which 2 L of groundwater was filled. The high pressurized cell maintained at 50 ℃ and 100 bar to simulate the CO2 storage conditions under the ground. The scCO2 – groundwater – sandstones reaction was reproduced in the high pressurized cell and physical properties of sandstones were measured at different reaction time (10, 20, 30, 60 and 90 days). The dry density and P/S-wave velocity decreased by 0.5 % and 2.6/4.7 %, respectively, for 60 days of the scCO2 - groundwater – sandstone reaction. The porosity of the sandstone core increased by over 10 % for 60 reaction days. The pH of groundwater dramatically decreased at the early reaction time, but the trend of pH decrease become gentle after 60 reaction days, suggesting that the weathering process of minerals actively occurs due to the low pH of groundwater at the early CO2 injection time. Actually, the mass of sandstone core decreased by 0.9 %, resulting from dissolution. The concentration of most cations in groundwater increased within 60 reaction days. The concentration of Na+ and Mg2+ increased from 386.20 mg/L to 603.30 mg/L and from 2.05 mg/L to 29.78 mg/L, respectively, after 30 reaction days. After 60 days, the concentration of Na2+ decreased from 605.30 mg/L to 534.77 mg/L and the concentration of Mg2+ decreased from 29.78 mg/L to 23.34 mg/L. It suggested that the precipitation of dissolved ions occurred. However, Ca2+ concentration in groundwater increased from 3.37 mg/L to 232.57 mg/L after 60 days. These results suggested that the calcite included in sandstone cores was easily dissolved by the reaction. Physical properties of the Janggi sandstone and groundwater quality were sharply changed at the early reaction time, but the rate of their changes gradually moderated after 60 reaction days. These results showed that the Janggi sandstone layer can be used to store scCO2 in stable because the geochemical reaction by CO2 injection become equilibrium within a short time. Through the results of this study, the sandstone of the Janggi basin is considered very available for the domestic onshore CO2 geological storage site. However, the pilot scale experiment has to be performed because these results were limited to the laboratory scale experiment.

Key word : Supercritical CO2, Janggi sandstone, CO2 storage rate, Physical property