Life Cycle Assessment - Development Planning through Decommissioning
Authors: Poremski Heinz Jochen 
Published: October 2008

This paper will discuss the decommissioning concept that is being advocated in Europe, in particular, the need to use Life Cycle Assessment {LCA)-based methodology as a tool for decision-making. LCA methodology comprises: goal and scope definition, inventory analysis, impact assessment and interpretation including options/proposals for the decision-making process. Energy and raw materials consumption as well as any emission into air, water, soil will be subject for the impact assessment and the subsequent interpretation. For the purpose of comparing the different options on decommissioning (e.g. disposal at sea/recycling and re-use onshore) of offshore installations, selected life stages (e.g. raw materials' sourcing, processing, manufacturing of the installation and decommissioning options) will be evaluated. The results of this LCA-based assessment can be used for those categories of offshore installations which are still subject for case-by-case decisions for a possible disposal at sea or alternative onshore treatment, including the recycling and/or re-use. Furthermore, LCA could assist in the development planning of offshore installations by indicating those life stages and processes where possible improvement/optimization with respect to energy/raw material consumption, installation/ de-installation processes and reduction of emissions can be achieved.

Introduction

Offshore oil and gas exploration and exploitation activities are meanwhile well-established technologies all over the globe. There are estimations(1,3) about 6,000.6,500offshore installations. They are distributed in:–Gulf of Mexico (4,000)–Asia (950)–Middle East (750) and–North Sea (600).

The construction, installation and performance of these oil and gas exploitation platforms was developed during the last 30 years to a hightechnology sector. The large majority of stationary platforms (&gt; 80%) are frame-shaped steel platforms, so called jacket platforms. They are used in different water depths (some 10 to 200 m) and their weights range from about 400 t (e.g. 150 t superstructure, 250 t substructure) up to 77,000 t (e.g. 31,000 t superstructure, 46,000 t substructure). Other types of platforms include the gravity base platforms which have a flat foundation. Their stability is created through high volumes of concrete and other filling materials (e.g. sand/gravel) used in substructures. These large platforms are used at water depths between 70 and 200 m, their superstructures have weights between 11,000 and 54,000 t and their substructures between 130,000 t and 800,000 t. These figures also illustrate the efforts which are necessary to be taken when decommissioning these installations after their average life-time of use, i.e. after about 20 to 30 years. There are different solutions which might be taken and which were taken in the past:–Leaving the platform fully in place: no further use, but maintenance/surveillance required and equipped with sea markings; utilization for a different purpose, e.g. monitoring station.–Partial removal down to a specified water depth (55 m, IMO): partial removal and dumping/emplacement at site; transport to and treatment on land (re-use/recycling disposal).–Complete removal: dumping/emplacement on site; transport and dumping at deep sea locations; transport to and treatment on land (re-use/recycling disposal).

The complete removal and transportltreatment onshore would be the most appropriate option under the aspects of:controlled waste treatment including re-use and recycling;–proper waste management according to mostly adopted and practiced procedures as