Evaluation of polyelectrolytic complexes based on poly(epichlorohydrin-co-dimethylamine) and poly (4-styrene-sulfonic acid-co-maleic acid) in the delivery of polyphosphates for the control of CaCO3 scale in oil wells
Polyelectrolyte Complex; Scale; Calcium carbonate; Squeeze Treatment
Polyelectrolytic complexes (PEC) based on poly(epichlorohydrin-co-dimethylamine) (EPI-DMA) and poly(4-styrene-sulfonic acid-co-maleic acid) (PSSMA) for polyphosphate encapsulation were first prepared in the literature. The PEC was developed in order to increase the durability of the treatment of scale in oil wells. Sodium hexametaphosphate (SHMP) was used as a model polyphosphate in this work and evaluated as a calcium carbonate scale inhibitor. The relationship between pH and CaCO3 formation was evaluated by static tests, dynamic precipitation in capillary and scanning electron microscopy (SEM) images. At pH 6.5, excellent results were found with complete inhibition of CaCO3 deposition in the capillary with only 2.5 mg L-1 of SHMP and a deformed structure of the CaCO3 crystals by SEM images was observed. In turn, at pH 7.5 and above, SHMP showed a significant decrease in the efficiency of scaling inhibition even at high concentrations. These results were attributed to the precipitation kinetics of CaCO3 under the drastic conditions evaluated. To optimize the PEC formulations, a 23 factorial design was applied. The resulting PEC suspensions were characterized by dynamic light scattering (DLS), zeta potential and SHMP encapsulation efficiency (EE). The best results were found by the formulation using 1% (w/w) of EPI-DMA, 0.1% of PSSMA and addition of SHMP before PSSMA. This optimized formulation was applied in real oil well conditions and showed good stability at 25 °C and reduced stability with increasing temperature. The PEC showed excellent inhibition efficiency against calcium carbonate scale with minimum effective concentration (MCE) of 2.0 mg L-1 using the same concentration of SHMP at 100 °C and 1000 psi. The PEC suspension also showed exceptional performance in the evaluation of the interaction with sandstone, improving not only the adsorption of the material in the rock grains, but also the durability of the treatment by 100%.