Behavior of mineral scale inhibitors applied in drilling of petroleum wells

The mineral scale or mineral fouling is from accumulating of inorganic salts, which cause problems to pipes and equipments applied in several industrial sectors. In the gas and oil exploration the mineral scale are formed by incompatibility between the chemical compositions of formation and injection waters and/or thermodynamic changes in the system during these activities. The prevention of scaling may be carrying out with the addition of chemical substances named scale inhibitors. In this work, two inhibitors containing functional groups of phosphonate and amine (IN-A) and polymerics (IN-B) were synthesized and investigated to application in the oil extraction in offshore Brazilian platforms. The studies involved the evaluation of compatibility of the inhibitors (IN-A and IN-B) with brines and their efficiencies to inhibit mineral scale related to calcium ions. In all the studies the brines were prepared with NaCl (76.50 g/L), CaCl₂.2H₂O (92.21 g/L), MgCl₂.6H₂O (14.42 g/L), BaCl₂.2H₂O (0.04 g/L), SrCl₂.6H₂O (6.33 g/l), KCl (11.59 g/L), Na₂SO₄ (0.68 g/L), NaHCO₃ (1.18 g/L) e NaCl (76.50 g/L) salts, aiming simulate the specific operational conditions in Brazilian platforms. The compatibility was evaluated by turbidity analyses and the efficiency by calcium ions analyses, later expressed in percentage terms. The IN-A showed better results of compatibility, showing turbidity values less than 10 NTU in all concentrations evaluated. The efficiency of the IN-A was also of, approximately, 80%, indicating a suitable chelating mechanism of inhibition with possible release of soluble complexes, according as expected. In contrast, the IN-B showed smaller compatibility with brines in the 5, 10 e 30 g/L concentrations, where the turbidity was of 12.7; 15.9 e 31.0 NTU, respectively. In addition, there was decrease in the efficiency of inhibition along the time in the higher concentrations so that in 30 g/L the efficiency was of 75.78% possibly due to difficulties in the solubility of the polymer and therefore cover-up of the active sites of the crystals. The results obtained allowed compare and evaluate the behavior of the two inhibitors synthesized, evidencing that the specific conditions of salt concentrations and solubility patterns are parameters very influents in the formulation and selection of the scale inhibitors.

Scale inhibitors; Supersaturated solutions; Oil extraction