The NEF Experience in Installing and Operating a Subsea Production System

ABSTRACT The NORTH EAST FRIGG Subsea Production System (SPS)(see Fig.l and ref.l) was the first multi-well SPS to deliver commercial gas when it came on 5 t ream on December r 8, 1983. The field has now produced for over a year with a remarkable high up time and is operated in an unmanned production mode as originally designed. This further demonstrates the suitability of such d concept for application o remote marginal gas fields. This paper reviews the main phases of the development of an SPS project :Design and detailed engineeringManufacturing and constructionOffshore activities, including completion and clean upProduction operations and presents the field experience gained. The author stresses that success is not granted, but results from extensive preparation efforts to maintain a high fabrication quality which is mandatory for SPS's. Emphasis is placed on the need of experienced personnel and for proven procedures to safely complete subsea gas wells in the North Sea winter season conditions. The project was completed on schedule and within the budget. The NEF total capital cost amounts to US $ 250 Million (1983) and the operating cost is about US $ 10 Million per year. These expenditures and some important items will be commented. As a conclusion, with its success NEF has demonstrated to be more than a suitable tool fur enveloping; a marginal subsea gas field in North Sea. It al so prove a that safe, reliable and economical SPS's are within the reach of present state of the art of subsea production technology, a fact of prime importance in the future of our industry. INTRODUCTION The NEF project was initiated by Elf Aquitaine Norge (E.A.N.) early in 1979 and was supported by its partners :Elf Aquitaine Norge A/S (operator)17.40%Esso Exploration-Production Norway58.00%Norsk Hydr'o Produksjon A/S 13.80%Totc;i Ndrine Norsk A/S8.70%Den Norske Stats Oljeselskap A/S 2.10% The experience SNEAP gained with the Experimental Subsea Station in GABON (Ref,2) and the Articulated Column ELFOCEAN (Ref. 3) benefited to NEF although its concept and specific components are different. The paper covers the different steps of the NEF development, describes the main difficulties encountered and concentrates on the major reasons that enable EAN to achieve a technica1 success at an economica1 cost. This statement is supported by selected technical results, statistics and cost tabulation to serve as a reference for those concerned with similar activities. KEVIEW OF THE DIFFERENT PHASES OF THE DEVELOPMENT The NEF development history was conventional and included four phases :Design,Fabrication - ConstructionOffshore works andProduction; these phases are summarized here below and the author concentrates on selected events and associated lessons.