Selecting the Field Development Concept for Ormen Lange
Authors: Gustavsson Fredrik , Eriksen Remi , Brekke Gunnar , Kraggerud Anne Gunnhild 
Published: October 2008

There are number of different ways of developing oil production fields in deepwater. Dry Tree Tieback Concepts ("Dry") require a platform to support the permanently attached production/intervention risers, but provide the efficiency and the convenience of direct well access for remedial activities. Subsea Tieback Concepts ("Wet") provide greater flexibility in utilization of existing infrastructure, well location and development schedules, but may require more challenging and costly well interventions/workovers.

The economics of deepwater developments are different from shelf activities. Deepwater developments are characterized by high capital expenditures, relatively low operational expenditures and high sustainable production rates - hence high costs for production interruption. The uncertainty related to whether "unforeseen" events will occur is increased as prototype and novel technology are introduced into an operating environment not encountered in shallow waters.

This paper describes the various solutions evaluated for the Ormen Lange field development project offshore Norway and how system reliability was factored into the concept selection process. The Ormen Lange field, which is the first deepwater discovery to be developed offshore Norway, is located 130 km from the West Coast of Norway at a depth of about 1000 meters. Developing Ormen Lange represents a major challenge with a combination of large water depth, extremely rough seabed conditions, long tie-back distance and demanding weather conditions. Concepts that were evaluated covers a full range of innovative solutions - ranging from a relatively novel "Subsea to Land" concept (subsea wells tied back to on onshore terminal) to a more traditional deepwater concept with an offshore processing facility with wet and dry wells.

The paper discusses the advantages and disadvantages with the various alternatives evaluated and outlines a rational approach to assess the consequences associated with component failures and flow assurance issues.

1. Introduction

Field development profitability is a function of many income and expense factors such as capital expenditures (CAPEX), operating expenditures (OPEX), production rate, product price and the frequency of component failures. Component failures reduce the field total production rate and increase OPEX. Regardless of the chosen concept, the ability to efficiently keep production wells on stream is one important factor determining field economic performance.

This paper demonstrates how RAM analysis successfully can be used in the decision making process of deepwater developments. The RAM methodology will be described, and some of the benefits of applying these techniques will be illustrated. One of the main results from this exercise is the potential cost savings related to focusing attention on critical areas, and improve solutions and concepts where the potential value-yield is highest. A second advantage emerging from this technique is the discovery of enhancement opportunities during the conceptual design phase rather than later in the development when cost of changes is much higher.

Several industry projects have recently been undertaken with focus on reliability techniques and economical optimization. The need to address challenges related to deepwater developments, and to allow for a better and more complete understanding, have been a driving factor to combine the industry's effort in Joint Industry Projects (JIP). The methodology and data described in the following sections are based on these projects.