## Abstract

In this study, a chemical model has been developed for the
simulation of the scale inhibitor (SI) interactions with carbonate systems
(calcite), where the aqueous phase may contain free calcium and magnesium ions.
The resulting model couples together the equations of (i) the carbonate system,
(ii) the speciation of the SI, modelled as a weak polyacid, H_{n}A,
(iii) the metal (Ca^{2+}, Mg^{2+}) binding – SI chelant
interactions and (iv) the subsequent precipitation of SI-Ca-Mg complex. These
reactions are considered in conjunction with the charge balance and mass
balances for calcium, magnesium, scale inhibitor and "carbon" (i.e.
the carbonate system aqeous components HCO_{3}^{-}, CO_{3}^{2-}and
CO_{2} and solid CaCO_{3}). This full equation set, with
suitable reduction, results in a system of 3 non-linear equations which can be
solved by the Newton-Raphson method to find the final equilibrium state of the
system.

The experimental results for the DETPMP/Calcite/Ca-Mg brine
system from a previous study were used to check the reliability of the proposed
model. The model calculates the equilibrium concentrations of all species (SI,
Ca^{2+}, Mg^{2+}, HCO_{3}^{-}, CO_{3}^{2-},
CO_{2}, H^{+}, and the components of the SI-Ca-Mg complexes
etc.) based on their initial values and reaction constants, i.e. equilibrium
constants, stability constants and solubility constants. The model can be
applied either assuming a closed chemical system, or an open system and
simuilation conditions were chosen in order to match the actual experiments
which were matched. The model results show good quantitative agreement with the
experimental results, although some assumptions must be made on the system
input constants. To elucidate the precise effects that these various parameters
are having in this very complex coupled system, an extensive sensitivity
analysis was performed. This is especially important for uncertain parameters
like stability constants of the complexes of scale inhibitor with calcium and
magnesium, which are not reported in the literature.

In future, this model be coupled with the adsorption model (based on the isothermal adsorption curve) and the coupled model will be incorporated into a transport model to develop a complete coupled adsorption/precipitation squeeze treatments simulation model. To our knowledge, no such model currently exists.

Original language | English |
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Title of host publication | SPE International Conference on Oilfield Chemistry 2023 |

Publisher | Society of Petroleum Engineers |

ISBN (Print) | 9781613998748 |

DOIs | |

Publication status | Published - 21 Jun 2023 |

Event | SPE International Conference on Oilfield Chemistry 2023 - The Woodlands, Texas, USA Duration: 28 Jun 2023 → 29 Jun 2023 |

### Conference

Conference | SPE International Conference on Oilfield Chemistry 2023 |
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Period | 28/06/23 → 29/06/23 |