Extra-Long Subsea Tiebacks Reduce Deepwater Development Costs
Authors: Feder Judy 
Published: September 2019

This article, written by JPT Technology Editor Judy Feder, contains highlights of paper OTC 28839, “Deepwater Innovations: Extra-Long Oil-Tieback Technologies,” by Michael Gassert, Gianluca De Molli, Vito Calabrese, Eniprogetti, and Stefano Magi, Gianfederico Citi, and Fabrizio Rollo, Eni, prepared for the 2018 Offshore Technology Conference, Houston, 30 April–3 May. The paper has not been peer reviewed. Copyright 2018 Offshore Technology Conference. Reproduced by permission.

It now appears possible to reduce deepwater development costs by increasing the distance between new assets and existing production hubs and shallow-water areas, or even connecting those assets to shore. The•complete paper presents and discusses the authors’ technology-development program regarding very-long oil-tieback architectures (50–100 km) and enabling technologies. The paper describes how the new technological solutions compare with more-conventional development schemes in concept-selection phases and discusses how the operator is preparing for potential implementation. The authors believe that the capacity to invest in and develop technologies required for long•and very-long tiebacks will decide the future of the deepwater subsea industry.

Introduction

Over the past few years, Eni and its partners installed more than 100 subsea trees, mainly on deepwater fields in various areas of the globe, in particular Angola, Norway, Indonesia, Ghana, Egypt, and Libya. The growing trend in subsea trees is guiding the operator’s needs and ideas about how to develop fields progressively around its production hubs.

In the evolution of deepwater oil fields, production floaters have been located close above the first fields to be developed. To guarantee the progressive infilling of the production hub, a first series of tiebacks was developed for a range of up to 15 km from the hub. The second series of tiebacks, ranging from 25–30 km from the hubs, is under development. Architectures and technologies to develop these tiebacks have been extensively studied, matured, and optimized, and some of those tiebacks are already in production.

New infilling fields are currently being explored and discovered at distances 30 to 100 km from production hubs, with new extra-long tieback architectures now under study. Those tiebacks will necessitate new technologies to enable managing the growing technical and economic challenges of subsea field developments. Long and very-long tiebacks that allow expanding from a brownfield perspective are likely to enable today’s greenfield programs.•

The paper reviews architectures and operation features of the operator’s currently installed short- and medium-length tiebacks to introduce the drivers and features of very-long tiebacks. The paper addresses sizing, operation targets, flow assurance, technologies, and related maturity.

Short- and Medium-Length Tieback Review

The operator’s initial deepwater fields have been developed with the production hub typically a few kilometers from the first main reservoirs in the direction of shallower water depth, allowing minimum distances dictated by drilling and offloading requirements. The main field is connected to the hub through a conventional wet insulated loop, which collects production from all the field’s drilling centers. Flowline diameters have usually been in the range of 10–12 in.