Materials Performance

MAR 2017

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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50 MARCH 2017 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 56, NO. 3 CHEMICAL TREATMENT This detrimental effect was more obvi- ous for Inhibitor C. In the presence of the surfactant/polymer mixture, Inhibitor C showed no inhibition efficacy at any of the tested concentrations. There was more CaCO 3 formed, as indicated by the negative inhibition (%) results, in solutions contain- ing the surfactant/polymer mixture and 2, 5, and 10 mg/L of Inhibitor C than in the blank solution. With 20 mg/L of Inhibitor C, the surfactant/polymer mixture decreased the inhibition (%) from >80 to 0%. These re- sults suggest that the overall CaCO 3 precipi- tation process, under the test conditions, was controlled by the surfactant/polymer mixture rather than the scale inhibitor. Further tests were conducted to evalu- ate the impact of the EOR surfactant and polymer separately. Results indicated that the polymer alone had little impact on the scale inhibitor performance. In fact, a small improvement to Inhibitor C was measured. The detrimental effect was largely caused by the surfactant, and the impact of this surfactant was further increased by the EOR polymer. For example, 20 mg/L of Inhibitor B provided 100% inhibition for so- lutions free of the EOR chemicals. Its effi- cacy was unchanged with the addition of only the EOR polymer, but was reduced to 50% in solutions with just the EOR surfac- tant. Efficacy was further reduced to 20% when the polymer was also added with the surfactant. Effect on CaCO 3 Morpholog y The impact of the EOR chemicals on CaCO 3 formation and inhibition were also ref lected in the crystal shapes of CaCO 3 precipitates (Figure 1). CaCO 3 cr ystals formed in the blank solution were predomi- nantly in the form of clustered hexagonal columns. Scale inhibitors at 2 mg/L showed little influence other than making the col- umn ends become ragged. Similar effects were also noticed for the EOR polymer. Some unusual morphologies developed with the EOR surfactant (either alone or combined with the EOR polymer). In the ab- sence of scale inhibitors, CaCO 3 crystals changed to short cylinders with rough sides or small particles (<10 mm) resembling rice grains (Figure 1[a]). In the presence of low concentrations of Inhibitor A (2 to 10 mg/L), oblate spheroid, biscuit-shaped, and dumb- bell-like crystals were formed (Figure 1[b]). At 20 mg/L concentration of Inhibitor A, f lower-like structures appeared (Figure 1[c]). The cylinder-shaped crystals became porous with Inhibitor B (Figure 1[d]). With the EOR surfactant alone, the prevailing shape with Inhibitor C was hexagonal col- umns (similar to Figure 1[a]), and with both the surfactant and polymer the structures were 5- to 8-mm nano rods (Figure 1[e]). Effect on CaCO 3 Polymorphs X-ray diffraction analysis results also showed that the EOR chemicals, especially the surfactant, can inf luence the CaCO 3 crystal structure. Of the three polymorphs that formed, calcite is the most stable and forms trigonal crystals. Aragonite is less stable than calcite, and its orthorhombic crystals convert to calcite at elevated tem- peratures. Vaterite is the least stable, and its hexagonal crystals convert to calcite at low temperatures. FIGURE 1 ESEM images showing CaCO 3 morphologies formed with different additives.

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