RIASSUNTO
Abstract
Following a very thorough planning process, initiated in the early nineties, the cessation plan for the Ekofisk I field was submitted to Norwegian authorities October 1999. Ekofisk I, containing some 14 steel jacket based and one concrete based installation, some 40 pipelines as well as some drill cuttings piles, is the most complex field ever being planned for cessation world-wide to date. The planning process has in most ways been pioneer work, both in a Norwegian and international context. In this paper a discussion and presentation of the planning process is given. As part of the planning, the work related to the Environmental Impact Assessment (EIA) plays an important role with regard to objectivity of technical assessments and openness to society and the public in general. In many ways this EIA has set the standard for future EIA's addressing offshore field cessation, both with regard to methods applied and presentation of findings. The paper presents the major steps in the EIA process, gives an introduction to methods applied, and presents the most important results from the objective assessment of the disposal alternatives.
Finally, the recommended solution is presented, including a discussion of criteria applied in reaching the decision, justification for the recommendation and a presentation of impacts related to the recommended solution.
Introduction
Field history.
The Phillips Norway Group (PNG*) discovered the Ekofisk field in 1969 and Ekofisk was the first field in the North Sea to commence production of crude oil. The Ekofisk field is situated in the central North Sea where water depths range from 66 to 78 metres. From first production in 1971 until 1999, over 350 million standard cubic metres of oil and condensate, plus 215 billion standard cubic metres of natural gas, were produced from the Ekofisk Area fields - giving a total tax revenue to the Norwegian Government in the order of 500 billion NOK (USD 66 billion). The field is operated by Phillips Petroleum Company Norway.
The Greater Ekofisk Area was developed step-wise and comprises the field center plus seven outlying (satellite) fields. In the mid-80's, the PNG observed that the seabed at Ekofisk was subsiding. To combat the effects of subsidence, the PNG elevated six platforms at the Ekofisk Center by six meters in 1987. In 1989 the PNG floated a concrete Protective Barrier Wall (PBW) in two parts to the field and installed it around the concrete Ekofisk 2/4 Tank to protect it against increased wave loads resulting from subsidence1. Despite the mitigating action taken to combat subsidence, by the early 1990's the Ekofisk facilities were showing their age, operating cost were rising, and new safety requirements for continued use of the Ekofisk Tank facilities and continued seabed subsidence presented uncertainties about the future. As a result, the PNG, in consultation with the Norwegian Authorities, decided to redevelop the facilities at the Ekofisk Center. The new facilities - known as ""Ekofisk II"" - were completed and put into use in August 1998. Ekofisk II will allow production of the Ekofisk Area long into the next century.
As a result of subsidence and the Ekofisk II development, and the fact that several outlying fields have reached the end of their economic life, thirteen platforms in the Ekofisk Area - twelve steel structures of varying sizes and the Ekofisk 2/4 Tank and its Protective Barrier Wall - are or will become redundant over the next fifteen years. Two additional steel platforms on the Norpipe Oil Pipeline are also redundant, and thus a total of fifteen redundant offshore structures require disposal solutions. Fig. 1 gives an overview of the field installations.
Field history.
The Phillips Norway Group (PNG*) discovered the Ekofisk field in 1969 and Ekofisk was the first field in the North Sea to commence production of crude oil. The Ekofisk field is situated in the central North Sea where water depths range from 66 to 78 metres. From first production in 1971 until 1999, over 350 million standard cubic metres of oil and condensate, plus 215 billion standard cubic metres of natural gas, were produced from the Ekofisk Area fields - giving a total tax revenue to the Norwegian Government in the order of 500 billion NOK (USD 66 billion). The field is operated by Phillips Petroleum Company Norway.
The Greater Ekofisk Area was developed step-wise and comprises the field center plus seven outlying (satellite) fields. In the mid-80's, the PNG observed that the seabed at Ekofisk was subsiding. To combat the effects of subsidence, the PNG elevated six platforms at the Ekofisk Center by six meters in 1987. In 1989 the PNG floated a concrete Protective Barrier Wall (PBW) in two parts to the field and installed it around the concrete Ekofisk 2/4 Tank to protect it against increased wave loads resulting from subsidence1. Despite the mitigating action taken to combat subsidence, by the early 1990's the Ekofisk facilities were showing their age, operating cost were rising, and new safety requirements for continued use of the Ekofisk Tank facilities and continued seabed subsidence presented uncertainties about the future. As a result, the PNG, in consultation with the Norwegian Authorities, decided to redevelop the facilities at the Ekofisk Center. The new facilities - known as ""Ekofisk II"" - were completed and put into use in August 1998. Ekofisk II will allow production of the Ekofisk Area long into the next century.
As a result of subsidence and the Ekofisk II development, and the fact that several outlying fields have reached the end of their economic life, thirteen platforms in the Ekofisk Area - twelve steel structures of varying sizes and the Ekofisk 2/4 Tank and its Protective Barrier Wall - are or will become redundant over the next fifteen years. Two additional steel platforms on the Norpipe Oil Pipeline are also redundant, and thus a total of fifteen redundant offshore structures require disposal solutions. Fig. 1 gives an overview of the field installations.