The Effects on the Immediate Environment Due to the Installation of the Ekofisk Protective Barrier
Authors: Broughton P. , Davies R.L. 
Published: October 2008

The Ekofisk Protective Barrier was installed around the existing Ekofisk Tank in the summer of 1989. The installation of this structure had an influence on the environmental conditions around the process/production equipment located On the Tank and now located within the Protective Barrier. Secondly, due to the large overall dimensions, the installation also had a major influence on the environmental conditions and environmental loading (due to waves and currents) acting on three adjacent steel platforms located immediately on the outside of the Protective Barrier. This paper presents the wind tunnel model test results indicating the relative increase in flammable gas cloud size and the relative decrease in the rate of dispersion of flammable gas clouds due to the installation of the Protective Barrier. These tests were conducted for various low wind speeds and directions in areas around production modules located on the +90 metres deck of the existing Tank structure due to enclose effects produced by the installation. The paper also presents the hydrodynamic model test results indicating the influence and effect of the installation this large structure On the magnitude of environmental wave loading acting on existing adjacent steel platforms.

1. INTRODUCTION

For reasons of subsidence at Ekofisk, the installations within the Ekofisk complex had to be protected against severe environmental action. Figure 1 shows the field layout of the existing platforms within the Ekofisk complex' Figure 2 shows a plan and elevation of the existing Ekofisk Tank, indicating the two main deck levels at +90 metres and +l00 metres above seabed. The solution selected for the protection of the Ekofisk Tank was to provide an external Protective Barrier. A plan and elevation of this structure is shown in Figure 3. An account of the main design and installation aspects of the Protective Barrier to surround the Ekofisk Tank has been given previously (1). The existing Tank structure supports a large amount of production equipment located onthe two main deck levels, and the partial enclosure of this equipment by the Protective Barrier represents a unique situation. Whilst providing complete protection to the existing Tank and production equipment from wave effects, the Protective Barrier considerably modified the ventilation characteristics of the original platform with the attendant increased risk due to the consequences of releases of hazardous gases. Because of the large overall outer dimensions of the structure (especially in the wave zone), of 137.5 metres diameter, the installation had a significant and unique effect on the immediate wave environment and consequently on the wave and current forces acting on the adjacent steel platforms. The purpose of this paper is to present two technical aspects. These are related to the consequences of the installation on the environmental conditions (wind) on the inside of the Protective Barrier, and secondly on the environmental conditions (waves and currents) on the three steel platforms located close to the outside of the Protective Barrier.

2. OUTLINE SCOPE OF WORK FOR WIND TUNNELMODEL TESTS

Due to the installation of the Protective Barrier around the existing Tank, studies of platform safety had identified two major sources of potential hazard to be:–flashed Off gas from an oil spill on the +90 metres deck (designated HI),