51314-3766-Scale Prediction for Iron Zinc and Lead Sulphides and Its Relation to Scale Test Design

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Product Number: 51314-3766-SG

ISBN: 3766 2014 CP

Author: Cyril Okocha

Publication Date: 2014

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The accurate prediction and management of oilfield sulphide scales such as iron sulphide is an important issue inoil production. This has become particularly significant as high temperature high pressure (HTHP) fields are beingbrought into production and the life of mature fields is being extended. In such systems additional scales such zincand lead sulphide (ZnS and PbS) are often being reported.This paper presents a detailed description of a sulphide modelling approach leading to the prediction of saturationratios and masses of the formed sulphide scales final solution compositions final pH levels etc. The equilibriumequations for the sulphide system are derived and solved in a manner in which they are compared directly with theexperimentally measured quantities. The actual Saturation Ratios (SRs) (e.g. SR = [Fe2+][S2-]/KspFeS) arecalculated for the various experiments and the prediction model is used directly to the design the details of thesulphide scaling experiment in the blank solutions.A number of calculated examples are presented and some key predictions of the sulphide scaling model are testedexperimentally for FeS ZnS and PbS systems. The quantitative agreement between the predictions of the model andthe experiments are very good. The resulting sulphide test methodology is thus very well underpinned theoreticallyand it is then applied to evaluate some examples of proposed commercial sulphide inhibitors/dispersants.