A Regional Shallow Stratigraphic Framework Off Mid Norway and Observations of Deep Water "Special Features"
Authors: McNeill A.E. , Salisbury R.S.K. , Østmo S.R. , Lien R. , Evans D. 
Published: October 2008

A joint industry initiative known as the Seabed Project has been established to investigate seabed conditions on the Mid Norwegian continental slope. This is in connection with deep water exploration licences awarded in the 15th Licencing Round, and involves the creation of a regional shallow seismic and geotechnical database covering an area of some 100,000 square kilometres. Building on previous work this paper presents results from the interpretation of over 10,000 km of new and reprocessed 2D seismic. The study has highlighted a number of different geohazards which must be carefully considered when planing future site investigations for exploration purposes. Such assessments can now be completed within the regional seismostratigraphic framework established during the study. Water depths in the study area range between 200 and 2500 metres. The main structural elements are the Mare and Varing Basins together with associated flanking basement highs. Sediments of mid to late Tertiary and Quaternary age have been investigated, and consist predominantly of thick sequences of glacigenic debris flows, slide sediments andunconsolidated hemipelagic sediments. The area includes part of the North Sea Fan and a number of slides and slumps including the Storegga Slide, one of theworlds largest. Other special features include sediment creep, diaprism, shallow faults, shallow gas, fluid escape features, evidence of gas hydrates and igneous intrusions. The understanding of the geological processes, which have shaped the continental slope and given rise to geohazards relevant to future exploration work, has been greatly enhanced by this work. As a joint industry initiative it is expected that the interpretation database will be extended by the acquisition and interpretation of Phase III data, currently ongoing, and input from 3D surveys and site surveys carried out by the operators and data from the European North Atlantic Margin (ENAM) project.

Introduction

The Seabed Project programme is multifaceted and designed to maximise operational safety related to the work of the petroleum industry in Norway as it takes its first steps into the deep water areas off Mid Norway. The programme is managed by Norsk Hydro on behalf of the operators of deep water licences awarded in 15th Licencing Round, i.e.: BP Norge, Esso Norge, Norsk Hydro, Norske Shell, Saga Petroleum and Statoil. The part of the programme which focuses on the seabed conditions and shallow geology has been divided into three phases, namely Geological and Geophysical (G & G) Interpretation Phases I, II and III. Phase I was carried out by the IKU, part of the Sintef Group based in Trondheim. This first phase involved the interpretation of 4100 kms. of an open grid of largely reprocessed conventional 2D digital seismic data. This was in order to establish a seismostratigraphical framework for the shallow geology (approximately the upper 1500 metres belowseabed) and identify features of importance, so as to gain an understanding of the geological and engineering conditions and to recommend additional work to be performed to aid this understanding. During 1996 additional high resolution 2D multichannel seismic data, together with mini sleeve gun, deep tow boomer and swathe bathymetry data were acquired on a regional grid in water depths between 400 and 1800 metres to compliment the Phase I data.