Well-data-based prediction of productivity decline due to sulphate scaling Pavel Bedrikovetsky a, ⁎, Raphael M.P. Silva b , José S. Daher c , José A.T. Gomes c , Vera C. Amorim c a University of Adelaide, Australian School of Petroleum, Adelaide SA5005, Australia b North Fluminense State University — UENF, Laboratory of Petroleum Engineering and Exploration — LENEP Rua Sebastiao Lopes da Silva, 56. Riviera Fluminense, Macaé, 27937-560, RJ, Brazil c PETROBRAS/UNBC, Avenida Elias Agostinho 665 CEP 27913-350 Imbetiba, Macae, RJ, Brazil abstract article info Article history: Received 9 December 2006 Accepted 7 June 2009 Keywords: reactive flow porous media sulphate scaling productivity index formation damage Sulphate scaling can have a disastrous impact on oil production in waterflood projects with incompatible injected and formation waters. This is due to precipitation of barium/strontium sulphate from the mixture of both waters and the consequent permeability reduction resulting in loss of well productivity. The system where sulphate scaling damage occurs is determined by two governing parameters: the kinetics coefficient characterising the velocity of chemical reaction and the formation damage coefficient reflecting permeability decrease due to salt precipitation. Previous work has derived an analytical model-based method for determination of two coefficients from laboratory corefloods during quasi-steady state commingled flow of injected and formation waters. The current study extends the method for determination of kinetics and formation damage coefficients from production well data consisting of barium concentrations in the produced water and of well productivity decline. We analyse production data for five wells from giant offshore field A, submitted to seawater flooding (Campos Basin, Brazil), and obtain values of the two sulphate scaling damage parameters. The two coefficient values were used for prediction of productivity decline for these wells. The values of kinetics and formation damage coefficients as obtained from either laboratory or field data vary in the same range intervals. These results validate the proposed mathematical model for sulphate scaling damage and the analytical model-based method “from lab and wells to wells”. © 2009 Elsevier B.V. All rights reserved. 1. Introduction The Ba/SrSO 4 scaling is a chronicle disaster in waterflood projects with incompatible injected and formation waters. This phenomenon is attributed to precipitation of barium/strontium sulphate from the mixture of both waters and the consequent permeability reduction resulting in loss of well productivity (Oddo and Tomson, 1994; Sorbie and Mackay, 2000). The sulphate scaling productivity decline phenomenon has been long recognized in North Sea reservoirs (Mackay et al., 2002) and in Campos Basin fields of Brazil (Bezerra et al., 1996; Rosario and Bezerra, 2001; Gomes et al., 2002). Decision-making on scale prevention, removal and on stimulation of scaled-up wells is based on scale damage prediction provided by reliable mathematical modelling with coefficients determined from laboratory or field data. Several numerical (Rocha et al., 2001; Delshad and Pope, 2003; Mackay, 2002) and analytical (Woods and Parker, 2003, Araque- Martinez and Lake, 1999) models describing sulphate scaling under laboratory and field conditions are available in the literature. Chemical reaction options in commercial simulators allow for sulphate model- ling on field scale (Eclipse, 2001; Stars, 2003). Mathematical models for sulphate scaling contain the reaction rate coefficient characterising the intensity of chemical reaction (so called reaction velocity). The reaction rate coefficient is proportional to flow velocity for small velocities, and the proportionality coefficient is called the kinetics coefficient (Fogler, 1998; Lopes, 2002; Bedrikovetsky et al., 2006a,b). The kinetics coefficient is determined by properties of rocks and fluids, by shape of deposit and by thermodynamics conditions. Another governing parameter is the formation damage coefficient reflecting permeability decrease due to salt precipitation (Pang and Sharma, 1994). The formation damage coefficient also depends on rock and fluid properties. Like permeability or capillary pressure, the kinetics and formation damage coefficients cannot be predicted theoretically for real rocks and fluids. Scale deposition profile during coreflood is non-uniform because the reagent concentrations decrease along the core due to chemical reaction. So, the sulphate scaling coefficients cannot be directly measured in reactive coreflood tests. The same applies to scale deposition around production wells. Therefore, the coefficients must be determined from either laboratory or field data by solution of inverse problems. Journal of Petroleum Science and Engineering 68 (2009) 60–70 ⁎ Corresponding author. Tel.: +61(8)83033082. E-mail addresses: pavel@asp.adelaide.edu.au (P. Bedrikovetsky), monteiro@lenep.uenf.br (R.M.P. Silva), daher@petrobras.com.br (J.S. Daher), zeadilson@petrobras.com.br (J.A.T. Gomes), vcfa@petrobras.com.br (V.C. Amorim). 0920-4105/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.petrol.2009.06.006 Contents lists available at ScienceDirect Journal of Petroleum Science and Engineering journal homepage: www.elsevier.com/locate/petrol