It is recognised that chemical interactions between scale inhibitor (SI) and corrosion inhibitor (CI) result in a reduction in the performance efficiency of both chemicals. As reservoir production systems become ever more complex, the requirements for chemical compatibility become greater. This is a particular concern for satellite and deepwater fields in which several wells may be co-produced through very long subsea tie backs. In such systems, chemical / chemical performance compatibilities are essential. Previous work on the issue has mainly been limited to field specific studies with a view to product selection or physical compatibility studies. Examples are drawn in this paper from field cases which demonstrate that interferences between the pre-selected candidate scale inhibitors and corrosion inhibitors can be a major concern. Indeed, final product selection is often based upon the combination of inhibitors that would not interfere with one another, rather than on the absolute performance of the individual products.
This paper then attempts to define and rationalise the chemical interactions from a scale prevention perspective. The performance of generic scale inhibitors including phosphonates (DETPMP), phosphino-polycarboxylates (PPCA), polyvinyl sulphonates (PVS) and sulphonate polyacrylate co- polymers (VS-Co) have been examined in the presence and absence of four different corrosion inhibitors including two commercial products and two genetic species (including an imidazoline and a quaternary ammonium salt). Furthermore, the impact of CIs on the adhesion of BaSO4 on metallic surfaces was also assessed both in the presence of SI and in the absence of SI as a means to define the interactions occurring.
INTRODUCTION
Chemical interactions between scale inhibitor (SI) and corrosion inhibitor (CI) products often produce a detrimental effect on the performance efficiency of both chemicals. ~,2,3 Work to date on this topic has focused largely on the physical compatibility, as precipitation has been noted following the combination of chemicals. Other studies carried out have been on a field specific basis 2, in which performance interferences between the SI and CI chemicals has controlled the final selection, as opposed to the individual absolute performance of the relative chemicals. Such physical and performance incompatibilities between products has become more important with the drive towards complex satellite reservoirs in which produced fluids from several wells and different fields can often co-mingle into single production lines. 2'4'5'6 This may mean that both CI and SI products may be delivered through a single umbilical and hence high concentration physical compatibility may be required. High concentrations of CI may be present at locations where severe scale formation occurs, requiting very effective scale inhibition and vice versa. Although several multi-functional (CI and SI) products are available 7'8'9'1° in many oilfield systems where high scale inhibition performance and high corrosion inhibition performance are required, combined products, rather than single multi functional products generally offer improved and more cost effective treatments.
