Permeability damage of coal for guar gel fracturing operation

Various fracturing fluids have been used forcoalbed methane (CBM) stimulations. The fracturing fluid can potentially cause permeability damage with an adverse impact on CBM production. In this study, we investigate the permeability damage behavior resulted from commonly used guar-based gel fracturing fluid. The anthracite specimens with the natural fracture and the hydraulic fracture were prepared and used.A series ofseepage experiments were conducted to test thefracture permeability evolution after gel injection and during water flushing. The result shows that the guar gel can cause serious damage to the coal permeability for both hydraulic and natural fractures regardless of the guar concentration. The gel residue leads to more serious permeability damage to the natural fracture compare with the hydraulic fracture. Under good gel breaking conditions, the fracture permeability can rebound through waterflushing.However, high guar concentration ofthe gelwas found to result in the uncompleted gelbreaking, thereby making it difficult for the hydraulic fracture and natural fracture to get good permeability recovery during water flushing. The findings of this study can provide guidance for the technology optimization of the guar-gel fracturing in CBM reservoirs.