Influence mechanism of inorganic salts on coal permeability during foam fracturing

To investigate the effect of inorganic salts on coal permeability during foam fracturing stimulation, the foam fracturing fluid was prepared with cetyl trimethyl ammonium bromide (CTAB) as the foaming agent and hydroxypropyl guar (HPG) powder as the foam stabiliser. Different concentrations of CaCl2, KCl, MgSO4 and NaHCO3 were added to obtained foam samples with different rheological properties. The effect of inorganic salts on coal seam permeability was systematically studied by seepage experiments. The results show that CaCl2 and NaHCO3 have a greater influence on the viscosity of foam fracturing fluid. The inorganic salt contained in the coal seam promotes the recovery of the permeability, and the high concentration of inorganic salt is more conducive to the recovery of the permeability of the coal sample. Among them, the permeability of coal samples treated with KCl can be recovered to more than 30%. The permeability recovery of coal seams is not only related to the viscosity of foam, but also to the types of inorganic salts. Inorganic salts promote the adsorption of CTAB on the pore surface while changing the liquid adsorption of coal seams, thereby changing the permeability of coal seams. The results have guiding significance for the development of foam fracturing technology.