Experimental Investigation of the Interaction between a Phosphate Ester Scale Inhibitor and Carbonate Rocks for Application in Squeeze Treatments

Studying the interaction between scale inhibitors (SIs) and chemically reactive carbonate minerals is crucial for determining SI retention in "squeeze" treatments. This study investigated the retention of the environmentally friendly SI, polyhydric alcohol phosphate ester (PAPE), on calcite and dolomite substrates. Elemental analysis of the supernatant solution as well as pH measurement and environmental scanning electron microscopy (ESEM) with energy dispersive X-ray analysis (EDX) were all used to investigate SI retention and to identify the morphology/composition of the resultant SI-Ca precipitates. Results revealed that PAPE was retained by calcite via pure adsorption at an initial test pH (pH ₀ ) of 4 and then precipitated at pH ₀ 6. In contrast, the PAPE/dolomite system was found to be effectively pH-independent, with precipitation dominating at both pH ₀ values. Any temperature effect was negligible for dolomite/PAPE retention, whereas with calcite, retention was smaller at lower temperature, which is attributed to the temperature-dependence of the substrate solubility. Overall, the final pH of the system and the resulting degree of SI dissociation contributed more to PAPE retention than did the final calcium concentration. EDX analysis confirmed scale-inhibitor phosphorus in the deposited solids, indicating coupled adsorption/precipitation. This phosphorus increased with the amount of precipitation and with the temperature, confirming the corresponding static adsorption test results.