Experimental Analysis of Geochemical Changes Caused by CO2 Injection: A Study of Lithuanian Saline Aquifers

Abstract The successful implementation of long-term carbon dioxide (CO2) storage in the subsurface requires an understanding of the CO2-brine- rock interaction, which tends to affect the petrophysical properties of the subsurface. This work evaluates the suitability of Lithuania's Baltic basin deep saline aquifers for long-term storage of CO2 by examining the geochemical behavior of CO2 when interacting with formation water and rock minerals. The Lithuanian reservoirs are composed of sandstones with quartz as the dominant mineral and minor traces of clays. These aquifers have shown potential for CO2 storage in terms of their depth and capacity. In the present work, the coreflooding apparatus was utilized to inject CO2 into rock samples and perform a series of experiments. Thes experiments investigated the impact of CO2 injection on rock samples with varying permeability and porosity. Initially, core samples were saturated with brine solutions representing Lithuania's saline aquifers’ salinity. Subsequently, saturated samples were placed in core holder, and brine injection was carried out to restore reservoir conditions. Following this, liquid CO2 was injected into rock samples. Impact of salinity, injection rates, and pressure effects were investigated. CO2 injection modeling was also performed to compare consistency of experimental results. The study measured the permeability of rock samples before and after CO2 injection at different brine injection rates (0.1, 0.3, 0.5, 0.9, and 1.5 mL/min). The results showed a drop in permeability following CO2 injection, which might be attributed to factors such as mineral alteration and salt precipitation, particularly at injection locations. This effect is consistent with findings from CO2 injection models over a 10-year period and observation over a 100-year period. The CO2 injection simulation modeling showed that significant changes in the formation's pH and porosity occurred near the injection site, while these parameters remained relatively constant farther from the injection site. Additionally, the low reactivity of quartz with CO2 suggested that negligible mineralogical changes were observed. This work highlights the importance of understanding the complex CO2-brine-rock interaction for safe gas storage in Lithuanian saline aquifers and also addresses the research gap in literature by providing experimental data in an area lacking such analysis. The present work emphasizes the need to enhance the research for long-term practical storage of CO2 in subsurface reservoirs.