Abstract
<jats:p>With the intensification of global climate change, reducing greenhouse gas emissions has become a global challenge. As a high-emission region, Ningxia faces significant pressure to reduce emissions. Geological storage of carbon dioxide is considered one of the key technologies for achieving carbon neutrality. Utilizing deep unmineable coal seams for CO2 sequestration can not only reduce greenhouse gas emissions but also increase the recovery rate of coalbed methane. However, the microscale interaction mechanisms between supercritical CO2(scCO2) and coal seams in this region are not yet fully understood. Therefore, this study selected the No. 6 coal seam of the Jurassic Yan'an Formation in Ningxia as the research object and conducted scCO2-water-coal simulation experiments using a high-temperature and high-pressure thermosimulation reactor. The experiments were set at 40°C and 9MPa to simulate a geological environment at a depth of 1000 meters. The simulation experiments were divided into four groups with durations of 1, 3, 5, and 7 days. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and inductively coupled plasma optical emission spectrometry (ICP-OES) were used to analyze the elemental migration characteristics of the reaction solution and solid samples. Low-temperature N2 and CO2 gas adsorption methods were employed to study the evolution characteristics of pore structures. The experimental results showed that the main elements in the reaction solution were Ca, Na, and Mg. Additionally, 14 trace elements were detected, with concentrations being relatively low. Among them, Cr, Pb, Cu, Zn, and Ti were detected in the reaction solution, but their concentrations were all below 3 ppm. Analysis of elemental migration rates indicated that Mo, Nb, V, Cu, Rb, Pb, and Zn had high migration rates (average migration rates &gt; ±50%), while Be, Co, and Y had migration rates below 10%. Low-temperature gas adsorption experiments revealed that after scCO2 treatment, the micropores in coal samples significantly increased, mesopores (1-50 nm) decreased, and macropores (&gt;50 nm) slightly increased. This suggests that the microporous structure of coal seams was enhanced after scCO2 treatment, which is conducive to the adsorption and sequestration of CO2. Moreover, the release of potentially harmful elements was extremely low, indicating high safety for this region as a CO2 sequestration site. This research provides important scientific evidence and technical support for CO2 geological storage in Ningxia and even nationwide.</jats:p>