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

Abstract

To investigate the fracture morphology and expansion characteristics of coal seams by different fracturing methods using supercritical CO 2 , we carried out supercritical CO 2 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 CO 2 under the incremental temperature and incremental pressure injection method was stronger than that under the continuous injection method. (3) Compared with hydraulic fracturing, supercritical CO 2 fracturing showed smaller fracture tip lag lengths, smaller intruding pore throat widths, and more complex phase changes in fracture extension.