Detailed Description :

The Horne and Wren gas fields are operated by Tullow Oil (UK) Ltd with 100% equity and comprise two separate accumulations in the southern part of the Southern North Sea.

The Horne field straddles the boundary between Blocks 53/3c and 53/4b-F1 and the Wren field lies in Block 53/4b. The two fields are expected to produce at a combined rate of approximately 90 MMscfd for approximately 2 years. Thereafter, the fields may be abandoned and the NUI removed for possible re-use. Alternatively, tie-backs from surrounding fields, e.g. Wissey, may extend the life of the facility to as much as 10 years.

The Tullow Horne & Wren Fields Development comprises –

• A Normally Unattended Installation (NUI) with minimum facilities for gas production of up to 90 mmscfd at peak through two deviated wells.
• The two wells are to be individually metered for allocation purposes and commingled on the Horne NUI prior to export. The NUI will be tied back to the ExxonMobil Operated Thames AR platform by means of 20km gas export pipeline. Hydrate inhibitor will be supplied from Thames by means of a 2” pipeline piggy-backed to the 10” pipeline. After separation and metering on Thames AR platform, the gas will be exported to Tullow Oil’s Bacton Terminal for conditioning and export to the NTS.

Schedule

The minimum facilities platform is scheduled for installation in February 2005 with production start-up in April 2005. In order to accelerate the programme to first gas, the wells are predrilled and completed with a mudline suspension system and the wells tied back to the platform topsides following installation.

This is a fast track project taking just 16 months from engineering through to first gas.

Concept Screening

ode facilitated an ‘options screening’ workshop (using an ode developed in-house screening process : Fuzzy Logic) to generate and rank all the viable options for developing Horne, Wren and Wissey (future option). The option screening took into account order of magnitude impacts to the host platform and a consideration of the environmental impacts. There where 3 main option each with 5 variation making 15 in total.

The workshop was also tasked to develop CAPEX estimates for implementation of the preferred option.

The concept is a ‘wellhead on a stick’, replicating typical subsea facilities in a dry environment.

Power consumption has been minimised by analysing seasonal requirements and eliminating large consumers such that power generation can be achieved using helical wind turbines and Ormat generators.

Personnel access is achieved via boat landing rather than helicopter, thereby eliminating the need for a helideck and TSR facilities. Essential maintenance can be carried out during a single days visit and availability will be in the order of 99.999%.

The concept evaluation was underpinned by a focus on safety and the safety case requirements.

FEED

Host Platform Modifications : Thames AR platform

Using a base case of tie-back at bottom of an existing riser at the host platform ode evaluated the potential host facility modifications and assessed the viability of re-using existing facilities compared with new facilities.

Key factor in this study included; Preliminary flow characterisation, flow assurance, definition of hydrate inhibition requirements, Scope of Work for Thames Modifications

Environmental impacts assessments were also undertaken in this scope as with all elements of the FEED study.

Engineering Horne Platform (NUI)

Three minimum facilities layout options were considered along with two jacket options ; 4-legged jacket or monopile.

FEED study included; FEED Safety Case, Preliminary P&IDs, Calculations of Flowing Wellhead Temperatures, Access / Egress Philosophy, Power Cable Consideration, Operations & Maintenance Philosophy, Spares Holding Recommendations and identifying Required Topsides Availability.

Engineering (Pipeline)

FEED study included; Pipeline Tie-In Details, Pipeline Materials Specification, Free Span Analysis, Expansion Spool Design and On Bottom Stability.

Project Management Services

Under a separate Project Management Services contract, ode provides all project management for the development project through until first gas. This includes the Project Manager, Pipeline Manager and HSE Manager.