Use of an Integrated Approach to Optimise a Congested Brownfield Facilities Development
Authors: Roberts C. , Hansen K. 
Published: November 2015

Historically a number of large offshore fields in the Arabian Gulf have adopted a ‘hub and spoke’ type development concept, comprising of a number of remote Well-Head Platforms (WHPs) connected to a central processing complex via individual subsea pipelines. As these types of fields become more mature Enhanced Oil Recovery (EOR) Techniques may be required to maintain or enhance oil production rates. The addition of subsea and topside infrastructure becomes increasingly difficult to accommodate due to major legacy issues such as ‘hub and spoke’ type developments, with the associated significant subsea congestion that arises through individual pipeline tie-backs.

This paper presents a case study for a planned EOR development of an existing offshore field in circa 50m water depth located in the North Arabian Gulf. The existing facilities have been developed over several phases in a ‘hub and spoke’ manner over the past 50 years and hence are highly congested, especially around the central processing complex. Furthermore, the production fluids are highly corrosive due to the presence of CO2, H2S and high-salinity (produced) water. The EOR development requires extensive additional infrastructure, comprising of over 200 additional wells distributed over a number of existing remote WHPs, in order to maintain current oil production rates.

The paper describes how the numerous issues and risks associated with this development were resolved via the adoption of a holistic assessment approach considering the full project life-cycle. Due to the interdependency of the problem a multi-disciplinary approach, leveraging process and facilities, subsea and pipelines, and materials technology expertise, was essential in order to optimise the field layout and overall development concept.

The selected concept deviates from the traditional ‘hub and spoke’ type approach and instead takes the form of two off central-spine large diameter trunk-lines connected to numerous smaller diameter spur-lines. The trunk-lines are manufactured from Carbon Steel (CS) linepipe with internal corrosion managed via a continuous supply of Corrosion Inhibitor (CI) delivered by a small-diameter supply-line piggy-backed to the trunk-line. The spur-lines are manufactured from Corrosion Resistant Alloy (CRA) clad linepipe, thereby negating the requirement for continuous corrosion inhibition. Future tie-in flexibility is provided by additional subsea tees and subsea double block and bleed valves pre-installed on the trunk-lines.

The paper demonstrates that effective discipline integration enables a holistic review of competing solutions to be undertaken. This approach resulted in a number of value opportunities being realized on the project: Simple and robust production system.Straightforward pipeline installation campaign with flexibility for phased installation if required.Minimal number (and complexity) of pipeline crossings.Reliable and low lifecycle cost pipeline system with a reduced operations and maintenance requirements.Minimal extent of brownfield modifications.Provided fluid gathering flexibility for future drilling / reservoir development.