Influence of Supercritical CO₂ Fracturing Mode on the Fracture Morphology and Propagation Characteristics of Coal

To investigate the fracture morphology and expansion characteristics of coal seams by different fracturing methods using supercritical CO2, we carried out supercritical CO2 fracturing of coal bodies and analyzed the temporal and spatial evolution characteristics of coal body fractures based on the pressure–time curves, otoacoustic emission events, and CT structural characterization of coal samples. The following conclusions were made: (1) Tiny fluctuations were observed in the time–pressure curves before fracture, which indicated that the microfracture appeared in the specimen; when a larger range of fissures was produced in the coal sample, the pressure dropped rapidly. (2) The acoustic emission events indicated that the fracturing by supercritical CO2 under the incremental temperature and incremental pressure injection method was stronger than that under the continuous injection method. (3) Compared with hydraulic fracturing, supercritical CO2 fracturing showed smaller fracture tip lag lengths, smaller intruding pore throat widths, and more complex phase changes in fracture extension.