A two-phase near-wellbore simulator to model non-aqueous scale inhibitor squeeze treatments Oscar Vazquez ⁎, Eric Mackay, Ken Sorbie Institute of Petroleum Engineering, Heriot-Watt University, Edinburgh, EH14 4AS, UK abstract article info Article history: Received 16 March 2011 Accepted 4 December 2011 Available online 10 January 2012 Keywords: Non-aqueous Scale Squeeze treatment Placement 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 perme- ability 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. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Precipitation of inorganic mineral scale in producing wells, com- monly known as oilfield scale, is one of the biggest production chal- lenges of the oil and gas industry as oil reservoirs are becoming more mature and water/oil ratios increase. Oilfield scale is defined as a hard crystalline deposit resulting from the precipitation of miner- al compounds present in water. The crystalline deposits are formed due to the minerals adhering to solid surfaces. These solid surfaces may be in the reservoir, the production tubing, or the surface facili- ties. As such, the problems caused by scale deposits are many: forma- tion damage, blockages in perforations or gravel packs, restricted/ blocked flow lines, safety valves and choke failure, pump wear, and corrosion underneath deposits. Further complications are encoun- tered due to some scales being radioactive. The most common scales are carbonates and sulphates. Carbonate scales are mainly caused by CaCO 3 precipitation, due to reservoir pressure depletion, an increase in temperature or evaporation. Sulphate scales are due to the incompatible mixing of reservoir brine and injected water, normally seawater. Scaling is present in all the producing areas of the world; however, the severity of the scaling tendency varies from field to field, as does the degree of difficulty in managing the problem, from relatively sim- ple low temperature low pressure vertical platform wells to more complex high temperature and pressure wells, where compatibility and thermal stability are major concerns (Graham et al., 2001a; Chen et al., 2004; Wat et al., 2008), or carbonate reservoirs where the precipitation of pseudo scales may cause formation damage (Graham et al., 2001b), and complex deep seawater completions (Bogaert et al., 2007, 2008). Commonly, a scale inhibitor (SI) squeeze treatment is applied to prevent the scale formation in producing wells. It consists of the in- jection of SI solution into the formation through the producing well. This may comprise a one-off treatment when the well is completed, or batch applications usually known as scale inhibitor “squeeze” treatments. Squeeze treatments consist of the following five stages: (i) a preflush stage; (ii) the main treatment where the chemical SI, usually as an aqueous solution, is injected into the formation with a concentration ranging from 2.5% to 20%; (iii) an overflush, designed to displace the main slug to a desired depth into the formation Journal of Petroleum Science and Engineering 82–83 (2012) 90–99 ⁎ Corresponding author at: Institute of Petroleum Engineering, Heriot-Watt University, Edinburgh, EH14 4AS, UK. Tel.: +44 131 451 3609; fax: +44 131 451 3127. E-mail address: Oscar.Vazquez@pet.hw.ac.uk (O. Vazquez). 0920-4105/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.petrol.2011.12.030 Contents lists available at SciVerse ScienceDirect Journal of Petroleum Science and Engineering journal homepage: www.elsevier.com/locate/petrol