Development of a Suitable CaCO3 Scale Inhibitor System for use in Ultrahigh Temperature and Pressure Wells

Abstract

AbstractThis paper reports a case study on the selection of a HP/HT/HS scale inhibitor for CaCO3 precipitation in the ultrahigh temperature and pressure environment experienced in the TotalFinaElf Elgin-Franklin assets. The paper will outline the scale management, inhibitor selection and deployment strategies adopted for scale control in this extremely harsh environment. The downhole temperature in these wells can be up to 200ºC and pressures can exceed 16000 psi. Problems are further enhanced by large decreases in pressure over relatively short changes in well depth. The literature is scant on studies performed at these conditions and a thorough screening of a wide range of scale inhibitor products and deployment techniques is an essential asset to the continued exploitation of very harsh well conditions.A new, upgraded scale prediction routine has shown that CaCO3 precipitation will occur over the whole range of reservoir conditions. A wide range of scale inhibitor chemistries including sulphonated polymers, phosphonates and some novel development products have been screened using four industry standard techniques. Thermal ageing revealed any instability caused by thermal degredation of the inhibitor molecule and jar test compatibility experiments performed at field temperature showed chemical incompatibilities with field brines. Dynamic scaling loop experiments were performed on not only the fresh inhibitor chemistries but also on thermally aged samples. The thermally aged samples were also analysed spectroscopically to identify any breakdown products and mechanisms. Finally coreflood experimentation was used to highlight inhibitor return profiles over a simulated squeeze treatment and to look for any formation damage that may have occurred.