Impact of temperature and pH on calcite inhibition using innovative green scale inhibitors

Abstract

This experimental study aimed at predicting firstly the critical mixing ratio of two incompatible aqueous phases of formation water and seawater by PHREEQC (pH-redox-equilibrium conditions) at temperatures of 40, 70, and 90 °C. Secondly, the performance of two green scale inhibitors (SI) of folic acid and inulin was experimentally studied through standard static jar tests in order to determine the optimum concentration and pH at which the calcite mitigation would be maximized. The optimum pH values of 4 and 6 were respectively found for folic acid and inulin, at three investigated temperatures. Interestingly, the inhibition efficiency of these SIs increased with temperature which is advantageous for the oil reservoirs. SEM (Scanning Electron Microscopy) and TGA (thermogravimetric analysis) analyses were also carried out to discern the SIs’ inhibition mechanisms and thermal performance. The SEM results showed that folic acid and inulin would inhibit precipitation under the crystal modification and threshold inhibition mechanisms, respectively. Furthermore, TGA analysis showed that these green SIs would sustain high temperatures, although their weight losses (heating rate of 10 °C /min and T < 100 °C) were almost 3.25 % and 9.15 % for folic acid and inulin, respectively.