Influence of Sodium Ferrocyanide as an Alternative Inhibitor of Sodium Chloride Crystallization in Tight Sandstone Gas Wells

Abstract

In the process of producing gas reservoir, after the high salt formation water flows into the wellbore, the salt dissolved in the formation water will gradually separate out to form salt plugging due to the sharp decrease of temperature and pressure, resulting in the decrease of gas volume in gas wells. Chemical desalination is one of the important means to solve the problem of salt plugging. Sodium ferrocyanide was selected as an alternative inhibitor. Firstly, static technological parameters, such as inhibitor concentration, temperature, and service period were optimized, and the effect of pressure drop, temperature and flow rate on inhibitor performance was discussed. Then, the field application of the inhibitor in the blocked Daji 1 - 7 gas well was demonstrated. Results showed that the addition of sodium ferrocyanide significantly increased the chlorine ion concentration of formation water from 80.6 g/L to 144.1 g/L, which indicated that sodium chloride recrystallization was inhibited. Scanning Electron Microscopy (SEM) results revealed that the addition of the inhibitor induced the doping of several prismatic crystals into numerous dense small cubic crystals. The size of the cubic crystals reduced to 39 µm. The length of prismatic crystals in the presence of the inhibitor was only 200 µm and was less than that of crystals in the absence of the inhibitor.