This paper will focus on the laboratory and field challenges of maintaining productivity in a North Sea well through scale inhibitor deployment via gas lift. Calcium carbonate scale formation commonly occurs during early production of formation water and in this particular well was detected on the downhole safety valve and upper tubing. Several scale management options were considered, however, that considered most likely to succeed was inhibitor injection via the gas lift system.

An extensive laboratory evaluation under the North Sea field downhole conditions was undertaken in order to qualify a suitable scale inhibitor/solvent package. While the identification of a scale inhibitor capable of controlling calcium carbonate was relatively simple, the combination of an aqueous based inhibitor with a suitable solvent package proved challenging. The initial product development stage was focused towards identifying compatible blends of various types of scale inhibitors (phosphonates, polymers and vinyl sulphonate copolymers) with different solvent and solvent mixtures. An essential aspect of the formulation design was to minimise the potential for volatile loss from the product to the dry injection gas.

Several candidate scale inhibitor/solvent packages were put through a rigorous laboratory evaluation programme under the harshest possible conditions likely to be experienced in the field. From this initial review products were identified as passing pre-defined criteria and showed good environmental qualities with very low viscosities (5cP or less at ambient temperature) before and after volatile loss and had very low corrosivity (0.01mm/y). In addition, the chemicals displayed complete compatibility at concentrations in excess of 50% with the completion fluid, formation water and completion elastomers, and controlled calcium carbonate scaling at a relatively low concentration.

The final part of the paper will provide details of the field deployment experiences and challenges of the gas lift scale inhibitors developed.

You can access this article if you purchase or spend a download.