An Integrated Approach for Gas Dispersion, Gas Explosion and Structural Impact Analysis for an Offshore Production Platform on the Dutch Continental Shelf
Authors: Korndörffer W. , Schaap D. , van der Heijden A.M.A. , Versloot N.H.A. 
Published: October 2008

The design of an offshore gas production platform has been subjected to an extensive quantitative risk analysis in particular with regard to its resistance to gas explosions loads. It was demonstrated that integration of the physical and structural effects of a gas explosion in an early stage of the design results in a safe and economical design.

Introduction

In October 2003 gas was produced for the first time from the Wintershall Q4-C gas production platform located in the North Sea, 30 kilometres offshore the Dutch coast in a water depth of 24 metres (see Figures 1 and 2). The recoverable reserves of the gas reservoir at a depth of 2 kilometres are estimated to be 6 BCM. The reservoir is depleted by two wells and presently producing 3.5 MNm3 gas per day which is evacuated by a submarine pipeline via Unocal's Hoorn platform. The potential production capacity is 7.5 MNm3/day. The platform production facilities are based on the gas dewatering process. The platform is normally not manned. The design of the platform has been carried out by Korndorffer Contracting International (KCI BV), constructed by the construction yard HBG and installed by Seaway Heavy Lifting. The design and construction of the platform have been certified by Bureau Veritas. The Dutch State Supervision of Mines is the supervisory authority. As part of the safety case, an integrated gas dispersion, gas explosion and structural impact analysis has been carried out to assess the impact and risks of a gas explosion.(Available in full paper)

Platform Description

The Q4-C platform is a fixed structure consisting of a topside deck structure mounted on a jacket type substructure founded with skirt piles to the sea bottom.(Available in full paper)

Vent Stack.

The vent stack is 45 metres long.

Living Quarter and Helicopter Deck.

This module consists of an 11 men living quarter and a helicopter deck. The living quarter also contains, apart from the kitchen and living rooms, the control room for the platform. The second floor houses the sleeping quarters. This entire module weighs 400 tons.

Superstructure.

The topsides consist of three decks, which house all process equipment required to dewater the gas for transport to shore by pipeline. The topsides weight is 1800 tons.

Substructure.

The jacket is fixed to the seabed by means of eight skirt piles driven 35 meters into the seabed and supporting the topside structures. The jacket weight is 1200 tons.

Superstructure.

The superstructure is composed of three decks, being the main deck, production deck and cellar deck.

Main Deck.

The main deck supports the deck crane, helicopter deck and living quarters. This deck will be further used as well work over and maintenance operations and equipment. The remaining open area is reserved for future expansions like compression facilities.(is in the full paper)

Explosion Preventive and Mitigating Measures

In order to reduce the risks of a gas explosion on the platform, various preventive and mitigating measures have been taken into account in the design and operational condition.