Explore and practice of cryogenic fracturing in coal reservoirs of Qinnan Basin

Reservoir stimulation of coal seams is one of the important techniques to increase the production of coalbed methane. However, due to the unique cleat system and lithologic characteristics of coal reservoirs, the conventional hydraulic fracturing technology is found inapplicable in field applications. Based on the characteristics of low temperature, high safety, adsorption partial pressure and phase-change pressurization of liquid carbon dioxide, the cryogenic fracturing technology of coal reservoirs with liquid carbon dioxide was developed. The first coal seam freezing test was performed in Well X150-1 of the Qinnan Basin. The field test shows that liquid carbon dioxide forms ice crystals and also temporary plugging to divert fractures and enable continuous fracture propagation. Compared with the production data of the adjacent well X150-2, the technology reflects the advantages of short desorption time and high gas production of a single well after transformation from the perspective of later drainage and production effects. From the long-term drainage effect, after the liquid level drops to near the coal seam in the later stage, the daily drainage of Well X150-1 is relatively high, indicating better gas production potential. This technology is an effective supplement and development of conventional hydraulic fracturing technology.