Minimum Visit Concept As Applied To Unmanned Platforms In The Southern North Sea
Authors: Metcalf P.C. 
Published: October 2008

The paper is based upon the results of feasibility studies and conceptual designs completed in 1991 for Shell Expro UK, on the development of 'Minimum Visit' concept to be applied to existing gas producing installations in the Southern North Sea.

Maintenance and operational records were examined and existing system facilities were scrutinised and evaluated with respect to future unmanned operation.

The studies undertaken and the conclusions reached provide an invaluable guide to similar de-manning solutions for existing installations, and also provide valuable pointers for new gas, or oil producing offshore installations of a similar nature.

The principal conclusion of the work described in this paper was to confirm that a 'Minimum Visit' scenario could be developed based on six-weekly visits of one day to each platform for routine and breakdown maintenance supported with a short annual shutdown period. This resulted in major savings in terms of forecast operating costs.

INTRODUCTION

Shell Expro's Southern Business Unit and Stone and Webster Engineering Limited have recently completed Feasibility Studies, and subsequently Conceptual Designs for two platforms, in the application of the "Minimum Visit" concept.

This concept was originally developed to be applied specifically to existing manned installations in the Leman and Indefatigable Gas Producing Platforms in the Southern North Sea.

As a result of this successful design work, Stone and Webster has continued to develop the concept in this important area, for application to any unmanned, principally gas, but also oil, installations in areas like the Southern North Sea.

Many of the points raised and considered in this paper should prove to be relevant and important design factors in the development of unmanned operational philosophies anywhere in offshore areas throughout the world.

ADVANTAGE OF UNMANNED OPERATION

Generally, the philosophy of unmanned operation provides several advantages for marginal fields, whether for initial development, or for continuing cost effective operation with falling revenues as is the case in existing gas Fields. Some of the most important of these are:Less equipment required, as there is no need to provide a high level of utility support. Consequently CAPEX, and maintenance requirements are much lower.Lower operating costs from the point of view of manning levels, therefore lower OPEX.Lower overall complexity, and therefore theoretically higher platform availability from the point of view of producing hydrocarbons.

WHAT IS MEANT BY THE 'MINIMUM VISIT' OR MV CONCEPT?

The Minimum Visit (MV) approach has been developed specifically for Southern North Sea platforms although this could equally as well be applied to new installations. The main thrust of the MV concept, is to reduce to an essential minimum the number of visits required to an installation of a routine or emergency nature for operational reasons.

The definition of this minimum must be carefully balanced against the required availability of the installation to meet hydrocarbon production contracts.