RIASSUNTO
ABSTRACT
The development of the Occidental Group's North Sea Piper Field involves the operation of an oil loading terminal, with associated tanker deballasting problems, in the environmentally unspoiled Orkney Islands, Scotland.
If minimal upset to a finely balanced marine ecosystem is to result, the nature of both effluent and receiving waters must be thoroughly understood.
The multidisciplinary approach which led to system design, environmental appraisal and a comprehensive monitoring programme will be discussed.
INTRODUCTION
With the discovery of extensive reserves under the North Sea, Britain will receive an increasing proportion of its oil requirements from its own waters.
It was in January 1973 that the Occidental Group discovered commercially exploitable quantities of oil in the North Sea, in their Piper Field, which lies over 200 kilometres (125 miles) east of the N.E. tip of the Scottish mainland. In May 1974, another successful strike occurred in their Claymore Field, which lies close to the Piper Field. The recoverable reserves of the Piper Field are of the order of 650 million barrels with an expected peak production rate of 220,000 barrels per day, whilst the reserves of the Claymore Field are of the order of 250 - 500 million barrels.
Occidental decided to bring oil ashore from these fields by pipeline to a tanker loading terminal on Flotta, one of the southern islands of the Orkney group which lies 16 kilometers (10 miles) north of the Scottish mainland (Fig. 1).
Tankers arriving in Orkney to load with oil at the Single Point Moorings (SPM's) in the Scapa Flow, as described by Trainor et al (1976), will be ballasted with water collected in their previous port of cargo discharge. Ballast usually occupies up to 40% of the tanker capacity. This ballast, apart from containing any contaminants from the waters from the last port, will be polluted by oil from the previous cargo. The terminal must obviously include ballast treatment facilities to remove as much of this oil contamination as practical before the treated ballast water is finally discharged into the Orkney marine environment.
It is accepted with the present status of oi1-in-water treatment technology that some oil will be discharged in the effluent from the ballast treatment plant. However, in the construction and operation of the Flotta Terminal the necessity for protection of the marine environment of the Scapa Flow environs is recognized. This paper deals with the environmental criteria used to guide the design of effluent treatment and discharge, so that such discharges produce minimal impact on the marine environment.