Alkaline-Surfactant-Polymer (ASP) injection into an oil reservoir triggers a series of geochemical reactions including reservoir mineral dissolution and precipitation of scales inside the reservoir and wellbores. Modelling these reactions is important for understanding the processes and designing the ASP formulation for optimal oil recovery. A number of reactive transport modelling (RTM) approaches have been reported in the literature so far, but none has addressed the importance of a geochemical database underpinning such simulations considering both equilibrium and kinetic reactions. In the meantime, experimental data available outside the oil industry can be used for calibrating reservoir mineral dissolution equilibrium constants in high pH solutions.

In this paper, experimental data of dissolution of relevant reservoir minerals and precipitation of scale minerals are compiled and compared with predictions from the widely used geochemical modelling software PHREEQC. A new database calibrated to the experimental data is developed in PHREEQC format that can be used in Shell in-house reservoir simulator MoReS for ASP flood reactive transport simulations. In order to reproduce the sequence of the observed scale deposition during an ASP flood project, the kinetic rate laws for the mineral dissolution and precipitations have also been calibrated against the experimental data.

Significant differences in the predicted mineral dissolution and precipitation between the calibrated database and the one from the official PHREEQC release demonstrate the necessity of geochemical database calibration for high pH environments. With the calibrated equilibrium constants and kinetic rate constants in the new geochemical database, the sequence of secondary mineral (scale) deposition during ASP flooding as reported in literature can be successfully reproduced. The improved modelling capability for ASP scaling prediction also increases the confidence for other aspects of simulation results such as chemical breakthrough.

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