Synthesis and evaluation of scale inhibitor with high-temperature resistance and low corrosion capability for geothermal exploitation

Abstract

Scale and corrosion issues of well pipelines become more prominent in geothermal exploitation at temperatures exceeding 100 °C. Effective scale and corrosion inhibitors are the keys to addressing the concerns. In this study, maleic anhydride (MA), acrylic acid (AA), 2-acrylamide-2-methylpropane sulfonic acid (AMPS), sodium hypophosphite, and sodium dodecyl sulfate (SDS) were utilized to synthesize a multi-polymer scale inhibitor PZGS with high-temperature resistance and low corrosion capability for geothermal exploitation. The functional groups and molecular weight of PZGS were analyzed by Fourier transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC). The scale inhibitor contains carboxylic acid groups, amide groups, phosphonic acid groups, and sulfonic acid groups. These groups ensure the capability of PZGS to chelate Ca2+, thus promoting the lattice distortion of calcium carbonate scale and improving its scale inhibition performance and temperature resistance. The number average molecular weight and the weight average molecular weight of PZGS are 5446 g/mol and 7139 g/mol respectively. The scale inhibition rate of 480 mg/L PZGS could reach 95% at 150 °C which is better than common scale inhibitors such as nitrogen trimethyl triphosphonic acid (ATMPA) and diethylenetriamine pentamethylene phosphonic acid (DTPMPA), whose inhibition rates are just 62% and 60% at 150 °C respectively. With the increase of the concentration, the formation of aragonite and vaterite gradually increased while calcite decreased because of the chelation and lattice distortion of polycarboxylic acid groups, phosphonic acid, sulfonic acid, and other groups from PZGS over the calcium carbonate scale. The compound formula “240 mg/L PZGS plus 200 mg/L polyepoxysuccinic acid (PESA)" performed the best effectiveness in its anti-scale and low corrosion capability. Its scale inhibition rate on the calcium carbonate scale was 94.1% at 150 °C, and the corrosion rate of the KLF carbon steel corrosion test piece was only 0.35 g/(m2·h) due to the PESA film coverage. Compared with 0.94 g/(m2·h) from brine solution and 0.91 g/(m2·h) from 240 mg/L PZGS, the corrosion rate of the compound formula was reduced by 63.2% and 61.7% in simulated geothermal water respectively. The findings of this study can provide effective guidelines for the development of scale and corrosion inhibitors for geothermal exploitation.