## Abstract

In oilfield applications, various divalent cations are present in field produced waters, e.g. Ca<sup>2+</sup>, Mg<sup>2+</sup>, Sr<sup>2+</sup> and Ba<sup>2+</sup>. The interaction of these cations with phosphonate scale inhibitors (SI) is important both for scale inhibition and inhibitor retention mechanisms. In this paper, the properties of precipitated "mixed" Ca<sup>2+</sup>/M<sup>2+</sup> phosphonate SI complexes formed by 9 common phosphonate species are investigated, where M<sup>2+</sup> may be Mg<sup>2+</sup>, Sr<sup>2+</sup>, or Ba<sup>2+</sup>. These 2 and 3 metal ion complexes with SI are of the form SI-Ca<inf>N1</inf>-Sr<inf>N2</inf> and SI-Ca<inf>N1</inf>-Mg<inf>N2</inf>-Ba<inf>N3</inf>, where the stoichiometry N<inf>1</inf>, N<inf>2</inf> and N<inf>3</inf>, are the respective (M<sup>2+</sup>/SI) molar ratios. Static precipitation tests were performed varying the amounts of Ca<sup>2+</sup> and M<sup>2+</sup> present in the system (at a constant ionic strength), at 95°C, pH 8.5, and fixed [SI]= 2,000ppm. The stoichiometries of the solid precipitates were determined by re-dissolving the precipitated deposits in acidified distilled water (DW/HCl), and then assaying for Ca<sup>2+</sup>, M<sup>2+</sup>, and P directly, under each test condition, by Inductively Coupled Plasma (ICP) spectroscopy. It is shown experimentally that, for all 9 phosphonates tested, these stoichiometries depend on the number of M<sup>2+</sup> binding sites per molecule, solution pH, the relative SI binding constants to Ca<sup>2+</sup> and M<sup>2+</sup> at the test pH, and the solution molar ratio of M<sup>2+</sup>/Ca<sup>2+</sup>.

Original language | English |
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Publication status | Published - Jan 2015 |

Event | Corrosion 2015 - Dallas, United States Duration: 15 Mar 2015 → 19 Mar 2015 |

### Conference

Conference | Corrosion 2015 |
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Country/Territory | United States |

City | Dallas |

Period | 15/03/15 → 19/03/15 |

## Keywords

- Scale inhibitor phosphonate complexes calcium magnesium strontium barium binding precipitation stoichiometry

## ASJC Scopus subject areas

- Chemical Engineering(all)
- Chemistry(all)
- Materials Science(all)