Interaction of phosphonates onto the immobilized surface: application to scale control in oil and gas flow assurance

The flow assurance in oil and gas production faces several challenges related to scale formation and control. In order to assess scaling risk in pipes, set a realistic inhibitor limits for scale treatment and improve the efficiency of treatment techniques, a better understanding of the mechanisms that govern scale precipitation kinetics and the interaction between scale inhibitor and the immobilized surface is needed. In this study, a newly developed automatic titration method was firstly presented to simultaneously measure total alkalinity and weak organic acids concentrations of brine, which served as a robust tool to calculate the pH, bicarbonate concentration, and carbonate thermodynamic scaling tendencies at different conditions from downhole to wellhead. Scaling kinetics of CaCO3 and the phosphonate inhibitor (diethylenetriamine penta (DTPMP)) interaction with the CaCO3 surface was studied CaCO3 pre-coated steel tubing. Three stages including (1) induction, (2) initial deposition and (3) stable surface growth were observed during the scaling process, which can be described by the heterogeneous nucleation theory. With the presence of DTPMP, scaling process of CaCO3 was prevented by precipitation/dissolution of calcium phosphoante precipitates on/from the CaCO3 surface. DTPMP retention on the CaCO3 surface was facilitated by the coprecipitation of calcium carbonate and calcium phosphonate precipitates. Not only does this study contribute to the limited data base of scaling kinetics in absence and present with scale inhibitor, but also provides a new approach to better understand the inhibitor reaction with the subsurface