Review of Flow Assurance Solutions for Deepwater Fields
Authors: Denniel Sylvain , Perrin Jerome , Felix-Henry Antoine 
Published: October 2008

Flow assurance is among the main design issues for the development of deepwater fields. The hydrocarbon product must be transported from a remote well up to the topsides, without experiencing significant heat losses to the environment. In addition to high 'steady state' insulating performance, the system muat also provide good transient cool down behaviour to prevent the formation of wax or hydrate during shut down and to minimise the time required to resume production.

A number of solutions have emerged to address these challenges. These are high performance passive insulation, dual insulated lines allowing a pigging loop, extended cool down pipeline concepts based on phase change materials and active pipeline heating.

This paper compares the practicality, performance and cost of these generic concepts on the basis of some typical field development scenarios. It also presents a range of pipeline products developed and qualified by Technip on the basis of these concepts.

Introduction

Flow assurance has grown up as an engineering discipline with the emergence of deepwater field developments. It can be summarised as "the ability to produce fluids economically from the reservoir to a production facilities, over the life of field in any environment" (Deepstar). The severity of the consequences of many flow assurance issues have increased with the water depth and traditional shallow water operating procedures cannot always be applied. The main flow assurance challenges associated with deepwater are discussed and innovative pipeline design solutions are presented and compared. Technip have developed and qualified a number of systems, which enable the operator to develop deepwater fields in difficult flow assurance conditions. The technical advantages of these systems are summarized along with an estimate of their relative installed costs.

Deepwater Flow Assurance Issues and Solutions

What is Different About Deepwater?

The most significant characteristics are a low temperature and a dramatic increase of hydrostatic head pressure.

Most of the flowlines and riser sections will be exposed to a typical low seawater temperature of 4°C, which enhances heat losses to the environment. Numerous deepwater fields are characterized by a low well outlet temperature, especially offshore west of Africa [1].

The increased water depth and hydrostatic head magnify the energy loss of the production flow in two other main forms, which are:Joule Thomson cooling, which is a decrease of temperature due to the sharp gas pressure decrease at constant enthalpy.Potential energy loss. The significance of these two factors is increased in deepwater. It has indeed been demonstrated that a pipeline with infinite insulating performance will still experience temperature decrease in the in-field flowines, due to elevation changes, but especially in the riser section [1]. For this reason, a number of heated riser and integrated bundle concepts have been developed and are now included as part of field developments.

The deepwater conditions are ideal for formation of solid deposits such as hydrate and wax, with the risk to degrade or even kill the flow path. Figure 1 shows a typical hydrate formation curve. Combined pressure and temperature conditions located on the left handside of the curve are prone to high risk of hydrate formation.