Experiments to Evaluate Swelling Inhibition of Coal with High Salinity by Sodium Dodecyl Benzene Sulfonate Concentration

We studied coal specimens from the #3 coalbed of Shaoyang, Hunan province, to try to understand the processes the inhibited expansion of the coal beds. Experiments were designed to test the effect of the concentration of sodium dodecycl benzene sulfonate (SDBS) solutions on the swelling inhibition of the coalbed with five different high water salinities containing CaCl₂, and also the synergistic behavior between the SDBS, the Ca²⁺ and clay mineral were analyzed. The results indicated that: the swelling of the coals was mainly affected by its water salinity when either fresh water or solutions with low SDBS concentration was used as fracturing fluid additives. The coals with higher water salinity had the weaker hydration and the better relative stability. Besides, due to the attraction between Ca²⁺ and clay unit layer as well as the complexation reaction between Ca²⁺ and SDBS, the optimal SDBS solution concentration for the coals with five different water salinities（1000 mg/L to 5000 mg/L）are 200 mg/L, 400 mg/L, 200 mg/L, 300 mg/L, and 100 mg/L, respectively, and their swell increment was 0.18 mm, 0.1 mm, 0.11 mm, 0.13 mm, 0.1 mm respectively after 8 h. Furthermore, Within the scope of the water salinity of coalbed in this experiment, the expansion ratio of the samples can be determined by the fitting formula under the SDBS solution concentrations, thereby quantitatively predict the damage to coals caused by the fracturing fluid and then adjust the fracturing fluid formula to reduce the damage to the coalbed methane reservoir.