The law of the hydrogen ion diffusion coefficient in acid rock reaction

The diffusion coefficient of hydrogen ions is a key parameter for the acid reaction model calculation. The analysis of the law of the hydrogen ions diffusion coefficient in acid reaction is helpful to optimize acid fracturing technology design, and to improve stimulation. By introducing the power law fluid Reynolds number and the Schmidt number, the calculation method of the hydrogen ion diffusion coefficient was corrected for acid reaction kinetics parameter measurement apparatus with different acid viscosity. The new apparatus was designed and built in 2010, here it was used to investigate the law of hydrogen ions diffusion coefficient under various conditions by the tests of acid rock reaction rate. Combining the theoretical formula and acid rock reaction experiments, the laws of the acid rock reaction rate and hydrogen ion diffusion coefficient by gelled acid and in-situ gelled acid were obtained. The acid rock reaction experiments were performed by varying acid concentration, reaction temperature and flow velocity. The results showed that the rate of acid reaction can be accelerated by increasing acid concentration, reaction temperature and velocity. The degree of influence on the acid reaction is reduced by various factors result from increase of acid viscosity. When acid concentration is 0.006 mol/cm3, the hydrogen ion diffusion coefficient is minimum due to the trapping effect between hydrogen ions. The hydrogen ion diffusion coefficient increases as increase of acid flow velocity. When flow velocities of gelled acid and in-situ gelled acid are beyond 113.21 cm/s and 158.38 cm/s, respectively, the hydrogen ion diffusion coefficient tends to be stable.