The challenges of scale and corrosion control in a number of new HT/HP fields in the North Sea, such as the Heron cluster wells in the ETAP (Eastern Trough Area Project) development, are substantially more severe than those normally encountered. The extreme reservoir conditions (T > 175 °C, P ~13,500 psi, TDS > 350,000 mg/L), depths (~ 5 km) and the need for long tiebacks (26 km) along the sea bed, give rise to very large temperature and pressure changes throughout the production system. The high temperature and extreme water chemistries lead to faster scale nucleation and growth kinetics, and to a very severe corrosion potential, which is further exacerbated by the high flow velocities (> 25 m/s) and high shear stress (>500 Pa) experienced in the flow lines. Engineering foresight during the project development stages of this reservoir have successfully reduced the potential scale and corrosion challenges, for example by:

  • use of de-sulphated wash-water (DSSW) to reduce sulphate scaling potential;

  • use of high chrome steel production tubulars to reduce corrosion potential

Such "Engineering Solutions" have reduced the risk of the scale and corrosion problems to a level that is both manageable and economic using chemical treatments, albeit at relatively high levels of scale and corrosion inhibitors.

This paper describes the results and conclusions from an extensive series of performance experiments under the very severe conditions pertaining to the Heron cluster system.

Due to the number and complexity of production chemicals to be selected in this study, a "hierarchy" was established for the various species based on their relative impact to field development/operability. Although the effective application of a Threshold Hydrate Inhibitor was ultimately considered to be the highest priority for the economic development of the field, this paper concentrates on the demonstrated interferences between a pre-selected list of candidate corrosion inhibitors (priority #2) and scale inhibitors (priority #3).

Indeed, final product selection was based upon the combination of inhibitors that would not interfere with one another, rather than on the absolute performance of the individual products.

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