The effects of supercritical CO2 transient high-pressure impact on coal pore structure characteristics

Abstract

The impact of supercritical CO2 transient high-pressure fracturing on coal pore structure is studied here. This examination uses a CO2 fracturing test platform to obtained coal samples at fracturing pressures of 22.6, 26.7, and 30.6 MPa, and we investigated the effects of CO2 transient high-pressure impacts on the pore structure of the coal by means of low-temperature N2 adsorption experiments and CO2 adsorption experiments. The results demonstrate that the specific surface area of the coal samples increased by 60.4%, 200.7%, and 92.6%, and the cumulative total pore volume increased by 56%, 267%, and 77.8% under the pressure impacts of 22.6, 26.7, and 30.6 MPa, with a significant increase in the number of pores. The original pore morphology of coal can be changed by the supercritical CO2 transient high-pressure impact, and the creation of new pores across the whole pore diameter section can be catalyzed. The impact fracturing on the pore structure is mainly attributed to the impact of supercritical CO2 and extraction. The meso-pores and macro-pores of the coal are further expanded by the impact of supercritical CO2, while the micro-pores with chemical properties are primarily modified by the extraction. An impact pressure of 26.7 MPa has a more pronounced effect on the expansion of meso-pores and macro-pores, and its effect on micro-pores is less significant compared to that of the other two fracturing samples. Therefore, it is possible that a specific fracturing pressure can more effectively expand meso-pores and macro-pores while reducing the impact on micro-pores.