Abstract
Coal fine particles are easily retained in the propped fractures during hydraulic fracturing and CBM (coalbed methane) extraction, which seriously affects the gas–liquid permeability. In this paper, gas–liquid permeability test experiments of propped fractures under different retained coal fine particles concentration were conducted. The results showed that the retained coal fines discharge rate (Rd) and gas/liquid effective permeability (Kge/Kwe) decreased with the increase of the closure stress. As the gas–liquid ratio increased, the Rd of the propped fractures with retained coal fine particles decreased. The Kwe decreased significantly while Kge increased slightly, yet the gas/liquid effective permeability loss rate (lw/lg) rose. As the retained coal fine particles concentration in the propped fractures increased, both the Rd and Kge/Kwe decreased monotonously. When the retained coal fine particles concentration reached 10%, changing the gas–liquid ratio and.closure stress exerted little effect on the gas/liquid effective permeability. In addition, the lg/lw was inversely proportional to Rd within the propped fractures with retained coal fine particles. The research results are of guiding significance for optimizing the CBM extraction system, solving the problem of low gas–liquid permeability caused by retained coal fine particles, and promoting the smooth drainage of CBM.
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