Comparing the adsorption of carbon dioxide and methane in Carboniferous shale from the Qaidam Basin, China

Abstract

The differences in the adsorptions of methane and carbon dioxide are closely related to the geochemical properties and pore structure of shale, and this variability is of great significance for energy exploitation and environmental issues. In this study, the geochemical composition and nanopore distribution of four Carboniferous shale samples collected from different depths in the eastern Qaidam Basin, China, were analyzed. Isothermal adsorption experiments with CO2 and CH4 were carried out within a pressure range of 0–9 MPa at a temperature of 313.15 K. For the four samples, the amount of absorbed CO2 was 2–7 times higher than that of CH4, indicating that CO2 injection is promising for shale gas extraction in the Qaidam Basin. Based on the Langmuir model, a new parameter was introduced to represent the adsorption affinity of CO2 relative to CH4 of shale. This parameter is related to the Langmuir constant for shales. Its relationships with the organic matter content, mineral composition and pore structure are analyzed. The relative affinity parameter is useful for optimizing the pressure of CO2 injection to enhance the extraction efficiency.