Micromechanical response characteristics and control mechanism of SCCO2 injection into the semi-coke layer of tar-rich coal in-situ pyrolysis

Xiaolong Yang, Qingmin Shi, Shuangming Wang, Shidong Cui, Bingyang Kou and Chunhao Li

Energy, 2025, vol. 334, issue C

Abstract: Tar-rich coal in-situ pyrolysis (TCIP) can form developed pore-fissure structure spaces to provide an ideal storage vehicle for CO2 geological storage. To investigate the CO2 storage stability, tar-rich coal in-situ pyrolysis semi-coke (simulated burial depth: 1000 m; temperatures: 200 °C, 400 °C, 600 °C) was exposed to the SCCO2-H2O-coal system (12 days/10 MPa/45 °C) in this study. The influence of supercritical CO2 (SCCO2) injection on the micromechanical properties of the in-situ pyrolysis semi-coke layer was analyzed by nanoindentation, X-ray diffraction (XRD), and Raman. The results indicated that the increasing pyrolysis temperature significantly strengthened the micromechanical properties of the in-situ pyrolysis semi-coke layer, but there were variations in the mechanism of SCCO2 on different pyrolysis coal. For 200 °C pyrolysis coal, the extractive removal of low molecular compounds and CO2 adsorption swelling reduced the orderliness of aromatic structures and weakened their micromechanical properties. In contrast, for high-temperature pyrolysis coals with dense and ordered structures (400 °C, 600 °C), the constraint of the rigid skeleton resulted in CO2 adsorption swelling to squeeze the aromatic layer. This process enhanced intermolecular forces and promoted the tight arrangement of macromolecular structures, thereby causing a remarkable elevation in Young's modulus and hardness.

Keywords: Tar-rich coal; CO2 geological storage; In-situ pyrolysis; Nanoindentation (search for similar items in EconPapers)
Date: 2025
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Persistent link: https://EconPapers.repec.org/RePEc:eee:energy:v:334:y:2025:i:c:s0360544225031044

DOI: 10.1016/j.energy.2025.137462

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