Effect of CO2 on coal P-wave velocity under triaxial stress

• Published in: 矿业科学技术学报（英文版） Vol. 32; no. 1; pp. 17 - 26
• Main Authors: Shuangjiang Zhu, Jianhong Kang, Youpai Wang, Fubao Zhou
• Format: Journal Article
• Language: English
• Published: State Key Laboratory of Coal Resources and Safe Mining,China University of Mining and Technology,Xuzhou 221116,China 2022; School of Safety Engineering,China University of Mining and Technology,Xuzhou 221116,China; School of Safety Engineering,China University of Mining and Technology,Xuzhou 221116,China%Jiangsu Key Laboratory of Fire Safety in Urban Underground Space,China University of Mining and Technology,Xuzhou 221116,China; Jiangsu Key Laboratory of Fire Safety in Urban Underground Space,China University of Mining and Technology,Xuzhou 221116,China
• Subjects: Coal; P-wave velocity; CO2 sequestration monitoring; Triaxial stress condition
• ISSN: 2095-2686
• DOI: 10.3969/j.issn.2095-2686.2022.01.002

As P-wave velocity is sensitive to the variations in coal reservoir parameters,it is possible to monitor the injected CO2 through P-wave velocity during CO2 sequestration in coal.However,the effects of CO2 on the coal P-wave velocity under triaxial stress are not clearly discerned.In the present study,different bound-ary conditions and gases were utilised to investigate the factors affecting the P-wave velocity after the interaction of coal with CO2.Experiments with helium indicated that the pore pressure primarily affected the P-wave velocity by altering the effective stress.Experiments with CH4 and CO2 indicated that matrix swelling induced-cleats porosity decline significantly promoted P-wave velocity.Moreover,CO2 caused a wider scale and severe weakening of coal matrix than CH4,thereby significantly decreasing the P-wave velocity,and the decline in P-wave velocity increases with vitrinite content.Furthermore,experiments under different boundary conditions showed that with the boundary condition having more constraints,the decrement of pore pressure on P-wave velocity is more weaken,whereas the improvement of matrix swelling on P-wave velocity is more evident.This study contributes to understanding the mechanism of effect of CO2 on P-wave velocity under triaxial stress condition and provides guidance for monitoring CO2 sequestration in coal.