Coal Bed Methane (CBM) Stimulation by Liquid CO₂ Phase-transition Fracturing (LCPF) Technology

摘要

The permeability of coal seam is the main factor restricting the safe production of coal bed methane (CBM). In order to improve the extraction efficiency of CBM and reduce the probability of coal and gas outburst, it is of great significance to adopt artificial measures to enhance the connectivity of fracture network of coal reservoir. In this paper, the modification test of the fracture network in soft and low permeability coal seam is carried out by using the liquid CO_(2) phase-transition fracturing (LCPF) technology through cross-boreholes in bottom drainage roadway. The results showed that the diameter of the borehole is obviously increased, and the gas flow rate and gas concentration are greatly enhanced, which indicates that the pores and fractures of the coal reservoir are effectively connected, and the influence radius of gas extraction is about 10m. Although, at the later stage of gas drainage period, the pure gas quantity and gas concentration show a decay trend, they still maintained at a high level, which is favorable for CBM extraction. Compared with hydraulic fracturing, the LCPF technology has better effect on permeability enhancement of coal seam in the early drainage stage after fracturing. The LCPF technology not only enhance the CBM extraction efficiency, but also shorten the driving period of roadways.