Magnus: Use of Conductor-Sharing Wellhead Technology To Access Additional Hydrocarbons
Authors: Bybee Karen 
Published: February 2015

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 124233, ’Magnus: Utilisation of Conductor Sharing Wellhead Technology To Access Additional Hydrocarbons via a Slot Constrained Platform,’ by S.E. Hicks, A. Moore, SPE, and M. Honey, SPE, BP plc; I.R. Farmer, Schlumberger; B. Smart, SPE, and R. Ekseth, SPE, Gyrodata; and D. Brown, SPE, Cameron, originally prepared for the 2009 SPE Offshore Europe Oil and Gas Conference and Exhibition, Aberdeen, 8-11 September.

The Magnus platform in the UK northern North Sea has been producing since 1983, with all 20 original slots now occupied. Additional infill- and extended-reach-drilling production targets were identified, and a means of access was required while maintaining base field production. Platform modifications were selected because of significant commercial advantage over alternative developments. The Magnus jacket was modified to permit running of four additional large conductors into which two smaller casings could be installed.

Introduction

Magnus is the most northerly currently operated field on the UK continental shelf. Discovered in 1974, first production was established in 1983. Continual field development has resulted in more than 90 wells including exploration, appraisal, and development wells.

In 1995, production from a now-full well template plateaued, and a program of well-intervention work was begun. Extensive subsurface work focused on EOR mechanisms across discrete reservoir panels and identified multiple new injection and offtake points that would be required to optimize field production from each respective area. By the late 1990s, it became apparent that sidetrack options from existing wells alone would not permit full optimization of the Magnus EOR program.

The complexity and tapered profile of the Magnus-platform jacket prevented introduction of more than seven new drilling slots. To use newly constructed slots fully, conductors would have to be “split,” permitting two wells from surface to be installed per conductor. The full-length paper outlines the major challenges posed by conductor-sharing well design and outlines some solutions found to aid successful well delivery.

Magnus Extension Project (MEP) Platform Modification. The MEP was sanctioned in 2004, and the most suitable aspect for new well slots was found to be the east side of the platform, the same side as the drilling package. Only the east face of the platform allowed new conductors to be installed without clashes with existing infrastructure.

With the east face selected for new-slot location, options of seven 30-in. slots or four 46-in. slots were identified. MEP financial criteria necessitated provision of eight new wells, hence construction work for four new 46-in. “splitter” slots began in 2005.

Conductor Guide Frames. Installation of six conductor guide frames per new well slot was performed external to the platform jacket. The guide frames incorporated an asymmetric funnel design to guide rigid conductor pipe, incrementally building vertical deviation to 4° at seabed. Five of these preinstalled guide frames are installed subsea, and one was installed above sea level.