Abstract

The OTTER field is the first to use a "dual ESP" completion in a subsea field, the project was developed by TOTAL and its partner's in the Brent sand reservoir, in the UK North Sea sector.

This development consists of three horizontal open hole oil producers and two cased hole water injectors, drilled from a combined drilling template and production manifold and tied-back to the EIDER host platform 21km away. Each oil producer can deliver up to 20,000 BOPD, the field has been on production since October 2002. A risk of sand production during the life of the field was identified, therefore downhole sand control was deemed necessary.

Well longevity has a major impact on the global project economics. Achieving and maintaining sand free production through optimal completion design was therefore critical to the overall success of the development.

This paper describes the strategy adopted and the factors considered in the development of the sandface completion optimised for the field life. Decisions on the sand control technique decisions were made while drilling the well based on cuttings particle size analysis: too small would have lead to open hole gravel pack. By eosteering the horizontal drain to stay within the most competent a sand body it would be possible to use a Stand Alone Screen completion, which was considered as the best option (cost, risk, and efficiency). The operationnal experience gained and lessons learnt on the first well contributed to the design enhancements required for completion of the following horizontal wells.

Introduction

The OTTER field lies in the Northern area of the Northern North Sea on the egde of the Viking Graben area and is located in UK blocks 210/15a and 210/20d (refer to figure 1). The field is operated by Total E&P UK PLC on behalf of the joint venture partners DANA Petroleum (E&P) Ltd, Esso Exploration and Production UK Ltd and Shell U.K. Exploration and Production (Shell Expro).

The field (originally called Wendy) was discovered in 1977 by Philips Petroleum 210/15–2 well that was tested at 4746 bopd, however the field remained undevelopped until 2002 due to limited size of the discovery and the technical challenges involved. Fina Exploration acquired operatorship of the field in 1994 and a 3D seismic survey was performed. Interest in developing the field was renewed, and to prove reserves and well deliverability, a delineation well 210/15a-5 was drilled and tested in 1997. The results of this well were encouraging and a development screening study was launched. A further delineation well, 210/15a-6, was drilled in 2000 to confirm a field extension to the North prior to the launch of the development project.

Development Description

The development consists of three horizontal open hole oil production wells each equipped with dual ESP and two cased and perforated water injection wells to provide pressure support. The dual pump systems allow significant production acceleration and improved recovery, while retaining lift redundancy and operational flexibility.

The subsea equipment comprises of a four slots drilling template with integral production manifold, which were installed prior to the start of the drilling operations. Water depth at template location is 184 m. The delineation well 210/15a-5 located 35 m from the main installation is tied to the template for use as a water injector. The manifold is tied back to the EIDER platform, operated by Shell Expro, at a distance of 21 km.

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