Insulated Flowline Technology for Deep Water
Authors: Tucker R.N. , Hays P.R. , Antani J.K. 
Published: October 2008

Deepwater fields are economically developed using subsea completions, with hydrocarbon fluids typically conveyed via multiphase pipelines and flowlines to an existing shallow water host facility. These flowlines operate in a low ambient temperature, high external pressure environment, conducive to the formation of paraffin deposits or hydrates. The leading strategy to circumvent these deleterious effects is to minimize heat loss from the system using insulation. Since the experience base for such deepwater insulated flowlines is limited, the DeepStar 600 Committee on Pipelines, Flowlines, and Umbilicals initiated several studies during 1994–95, addressing three major categories of insulation systems: pipe-in- pipe systems, integrated towed flowline bundles, and non-jacketed systems. This paper helps to identify potentially viable systems, design techniques, emerging technologies, feasible materials, and technical limitations. The proper design of flowline insulation requires a balance among the high cost of the insulation, the intended operability of thesystem, and the acceptable risk level. The following information is presented to aid development planners and subsea flowline engineers interested in the development, applicability, and availability of this technology.

Introduction

The DeepStar joint industry program is researching technologies that will enable production of unprocessed well stream fluids from deepwater subsea trees to shallow water host process facilities or an existing pipeline infrastructure. The incentive for advancing this field development scenario is to significantly reduce capital costs by avoiding the installation of a local deepwater host.

The DeepStar scenario represented in Fig. I indicates that the water depth ranges from 3,000–6,000 ft with nearer term interests focusing below 4,500 maximum. Correspondingly, the offset distances required to reach a shallow water platform (-600 ft) range between 25–60 miles (Ref. I).

Economical long distance production of multiphase well stream fluids (oil, gas condensate, and water) can be achieved with an effectively insulated flowline by minimizing the costs, revenue loss, and risks from the following:Hydrate formation during steady state or transient flowing conditions;Paraffin accumulation on the inner pipe wall, that can result in flowline plugging or flow rate reductions;verse fluid viscosity effects at low temperatures which lead to reduced hydraulic performance or difficulties restarting a cooled system after a short shut-in; andditional topside facilities required to heat produced fluids to aid separation processes.

Pipeline and flowline insulation systems have been successfully used in shallow water applications. Few of these systems, however, have been used in depths beyond 1,000 feet, and there is no current experience with any of these insulation systems in the DeepStar water depth range. The DeepStar 600 Committee surveyed insulated flowline technology to identify potentially viable systems, emerging technologies, and design techniques applicable to deepwater.