Modelling of nonaqueous and aqueous scale-inhibitor squeeze treatments

The most common method for preventing downhole 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 paper presents the results of a modelling sensitivity study comparing non-aqueous and aqueous scale inhibitor squeeze treatments. The model described can simulate the effect on the treatment life of treatment solubility in the oil and water phases, treatment strategy, adsorption properties (from the water and oleic phases), viscosity effects and wellbore friction. Of particular interest is the relationship between inhibitor 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. The sensitivity study is carried out using purpose written software for scale treatments. The code is a two-phase flow, multi-component, multi-layer, radial or linear mathematical model capable of simulating both aqueous and non-aqueous squeeze treatments. The model considers the immiscible displacement of oil and water phases along with inhibitor transport in both phases and mass transfer between phases. It is capable of modelling kinetic and equilibrium adsorption and desorption from either phase. The model has been validated by comparison with analytical solutions, standard conventional single-phase squeeze calculations and multi-phase reservoir simulation calculations5. An example two-phase calculation of a specific field treatment is included, and the results are compared with the field return profiles.