A two-phase near-wellbore simulator to model non-aqueous scale inhibitor squeeze treatments

Abstract

The most common method for preventing downhole oilfield scale formation is by applying a scale inhibitor squeeze treatment. In this process, a scale inhibitor solution is injected down a producer well into the near wellbore formation. Commonly, these scale inhibitor treatments are injected as aqueous solutions. However, there are certain situations where an aqueous based treatment is not desirable, such as where relative permeability effects, water blocking, fluid lifting, chemical penetration or hydrate formation are of major concern.This two-phase flow multi-component, multi-layer, radial near-wellbore simulator is capable of modelling both aqueous and non-aqueous squeeze treatments. It considers the immiscible displacement of non-aqueous and aqueous phases, along with chemical component transport in both phases and mass transfer between both phases, and it is capable of modelling kinetic and equilibrium adsorption and desorption. It has been developed to study and optimise non-aqueous squeeze treatments. Of particular interest is the relationship between scale inhibitor chemical solubility in the carrier and in situ phases, and the choice of phase for the overflush fluid. The relationship can have a very pronounced impact on inhibitor penetration and squeeze lifetimes.Finally, the simulator was used to simulate a series of polymer non-aqueous scale inhibitor squeeze treatments deployed in the Heidrun field in the Norwegian sector of the North Sea. The simulation study consisted in matching the well water cut for the time of the treatments, followed by the derivation of a pseudo-adsorption isotherm, which is used to describe the SI retention in the formation. The initial pseudo-adsorption isotherm, derived from the first field treatment return concentration profile, resulted in very good matches for the other two consecutive treatments.