ABSTRACT:

The paper describes a research analysis for a production platform substructure for Russian Far East shelf with average water depth from 70 to 160 m (e.g. Sakhalin-3). The above-mentioned structure should operate in the most severe shelf conditions, which include seasonal ice or hard storm and earthquake. The basic goal is to assure the platform has the same resistance against wave loads as against ice and seismic loads. In these conditions fixed substructures are usually used. For example, the platforms:PA-A (installed at water depth of 33 m), PA-B (32m) and LUN-A (48 m) – gravity based structures are used at Sakhalin-2 field. But, it is known that for a sea depth 60 m and more the gravity-based platform stability for Sakhalin seismic conditions requires huge amount of solid ballast and very high pressure on soil and, correspondingly, the piled substructure requires large number of piles. At the same time, the floating platform that is insensitive to seismic load would usually be unable to withstand ice impact. This paper presents a new concept of semi-floating substructure for average water depth (from 70 to 160 m). The results have been confirmed by computer simulation performed for the project example. Feasibility of the proposed option for construction and offshore assembling operations has been studied relative to construction capability of Russian shipyards. The proposed substructure with only flexible risers becomes a reasonable structure as long as some innovations are applied - and this is the subject of the present paper.

INTRODUCTION

The present paper describes the concept of semi-floating type substructure (moored by a double mooring system) that is able to withstand both moderate ice impact (winter) and wave excitation (summer-autumn), and earthquake at any time. Idea for this proposal originates from joint study of Spar and TLP floating platform concepts (Chernetzov, Karlinsky, 2006).

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