Deposit Prevention of Mineral Scales Using a Universal Dispersant of Carboxymethyl Cellulose

Abstract

Summary As the world’s demands for energy and water increase, innovative technologies have been implemented to produce more energy and water, sometimes in unconventional fields. It brought in new challenges of highly saline water formation and souring of wellbore or formation. Under these circumstances, the conventional threshold inhibition methods might be ineffective in controlling mineral scales. To develop a new feasible method to manage more difficult mineral scale problems, we investigated a single approach to prevent complex mineral scales from deposition using a water-soluble polymer of carboxymethyl cellulose (CMC). We also examine the effect of the combination of conventional threshold scale inhibitors and CMC for complex mineral scale control. Our results showed that a polymeric dispersant of CMC successfully prevented zinc and lead sulfide, barium and calcium sulfate, and calcium and iron carbonate scales from deposition, similar to what we had observed previously with iron sulfide. CMC combined with phosphonate inhibitors of diethylenetriamine penta(methylene phosphonic) acid (DTPMP) or hexamethylene diamine tetra(methylene phosphonic) acid (HDTMP) also enhanced the inhibition performance of phosphonate inhibitors. PbS and ZnS were successfully dispersed in the presence of CMC as low concentrations of CMC as 2 mg/L for PbS and 5 mg/L for ZnS in solution passed through a 1.2-μm pore-size membrane. For barite scale control, the combination of CMC and DTPMP inhibited barite formation for 2 hours, while CMC for only 5 minutes and DTPMP for 18 minutes. The mass of barite deposit on 316 stainless steel was reduced by three-order magnitudes in the combination of DTPMP and CMC, compared with DTPMP alone. The scanning electron microscope (SEM) image of barite precipitated in CMC and DTPMP showed that its morphology was no longer a rhombic plate. According to the transmission electron microscope (TEM) image, the surface of barite was covered by CMC, and after a 6-hour reaction, its size was 45.6 nm, which was slightly larger than that at induction time (10–35 nm). Gypsum crystal formation was also inhibited for at least 6 hours in combining CMC and HDTMP. For calcite scale control in the presence of 20 mg/L of CMC, calcite formations and growth were prevented for 134 minutes, and particle sizes remained in the nanosize range (average particle size of 396 nm) for a 15-hour reaction. Iron carbonate treated with 200 mg/L of CMC-250k and CMC-700k was dispersed for at least 2 hours under our experimental conditions. This study demonstrated that CMC effectively performed as a universal dispersant bringing a new feasible method to manage complex mineral scale problems.