Examination of the effect of generically different scale inhibitor species (PPCA and DETPMP) on the adherence and growth of barium sulphate scale on metal surfaces

One of the major concerns within the oil industry is how to deal with scale formation, whether it is in the wellhead equipment, downhole pipelines or the actual field formation. This is because as the scale forms, it begins to deposit itself on the linings of the pipelines, within the equipment and the pores of the formation. The layers continue to build and eventually there is no passage through for the oil. The most effective way to deal with the problem of oilfield scale formation is the use of scale inhibitors, in order to prevent or delay the scale formation. In many scale performance studies, the emphasis is on determining scale inhibitor species that prevent homogeneous nucleation and growth, rather than examining their impact on their ability to prevent heterogeneous nucleation and growth at the metal surfaces such as the production tubulars themselves. The adhesion and growth of scale on metal surfaces is clearly a much more serious problem than precipitation within the bulk solution.

This paper presents results from an extensive series of “adhesion” experiments that examine the effectiveness of generically different scale inhibitor products at preventing barium sulphate adherence and growth at metal surfaces. Tests have been conducted under ambient conditions and under both laminar and turbulent flow conditions.

Results demonstrate that the presence of scale inhibitor, at levels marginally below their concentration required to completely prevent crystal growth, results in increased surface adhesion. Similar results are recorded for the different inhibitor species examined. Furthermore, the level of surface adherence is shown to be more severe under laminar conditions than for tests conducted under turbulent conditions. The indication is that bulk precipitation is being reduced by the presence of the SI which encourages the more thermodynamically favourable heterogeneous nucleation to occur onto surfaces already present. The SI then continues to prevent bulk nucleation and slow growth continues at the surface in order to reduce the system's overall supersaturation. Increased surface growth relates to the effectiveness of the SI at preventing bulk nucleation.