The demands of the offshore oil and gas and subsea cable markets for Improved geotechnical information in very deep water is stimulating rapid developments in sampling and in-situ testing systems, for both downhole and surface deployment. This paper describes the problems to be solved and the latest Fugro Group solutions to some of them.
The last twelve months has seen a large number of developments in the field of offshore geotechnics, particularly with regard to new site investigation equipment.
These developments have been in response to industry demands that are themselves being driven by new trends. These have included the continuing drive into ever-deeper water, the Increasing popularity of FPSOs and subsea structures for field development and the ever-increasing number of pipelines and communications cables being installed on and in the seabed.
This paper discusses the new trends in the oil, gas and cable industries and describes how Fugro has responded to these trends by developing new innovative geotechnical equipment.
The petroleum industry trend over the last few years has been to move away from the traditional jacket or GBS structure for new field developments towards the fast track FPSO or floater installations. This trend has been enhanced by the discovery of deepwater oil and gas reserves in areas such as the West of Shetlands, West of Hebrides, More and Voring Plateau m the Norwegian Sea and West Africa.
We have also observed over recent years an increase in activity in the internet cable market and the installation of pipelines in deepwater areas such as the Black Sea. Pipeline and trenching contractors are now recognising that trenching without adequate sods data can cause installation problems and premature ageing on the pipe.
For the purposes of this paper we are defining ‘medium deepwater’ for water depths between the break in the continental slope (approximately 200m) to 700m water depths. ‘Deepwater’ is defined as water depths greater than 700rn.
Deepwater areas tend to be further from land and therefore are exposed to extreme variations in metocean conditions. The weather windows for performing field work are short compared to the predictable North Sea working windows and fieldwork in the deep water areas tends to be restricted to the summer months. Due to the water depth umbilicals have to be considerably longer. The sod conditions we have encountered are generally very soft, often brittle and are very different to previously experienced sods on the continental shelf.
Figure 1 shows a comparison between the comparative survey coverage between shallow and deepwater environments. The comparison shows that for a typical North Sea platform development a geotechnical site investigation would extend to between 80m and 100m below seabed and the corresponding site survey would cover a relatively small area (1–3 km2). Where as the geotechnical investigation for an FPSO development in medium to deep water would extend to approximately 30m below seabed and the corresponding geophysical site survey would cover (10–20 km2).