Justin Tuohy Publications

Flexible Pipe Technology – Spanning the Water Column in Deepwater Field Developments

Published: November 2002 | OSEA (Offshore South East Asia) Conference | October 29 – November 1, 2002 | Singapore

Abstract

The recovery of hydrocarbons in water depths up to 2000 metres to date and in the future beyond these water depths, presents significant technical challenges to the designers of recovery systems. Met-ocean characteristics, relatively low reservoir temperatures and pressures also serve to compound these challenges. Flexible pipe has become synonymous with the use of floating production systems spanning the water column, connecting subsea structures to facilitate the retrieval of hydrocarbons and the injection of water and gas. Innovation to unbonded flexible pipe’s technically complex multi-layer structure of helically wound metallic wires and tapes and extruded thermoplastics has ensured that the
product remains one of the key enabling technologies, particularly for deepwater developments. Recent developments include the application of flexible pipe technology in hybrid risers systems, large diameter export loading lines, and topside high-pressure applications.
This paper discusses Halliburton Wellstream’s approach to the use of innovative design techniques to ensure that the company is positioned at the forefront of new flexible pipe technologies. Case studies will be used to illustrate some of the existing technological breakthroughs provided by Wellstream and already in operation at various water depths world-wide. An insight into a typical comprehensive test programme associated with the qualification of a new product is also provided.

 

Authors:

Tuohy, J., Martin, S.

Justin Tuohy Publications

Application of Finite Element Modelling in the Qualification of Large diameter Unbonded Flexible Risers

Published: June 2002 | 21st International Conference on Offshore Mechanics and Arctic Engineering | June 23, 2002 | Oslo, Norway

Abstract

Unbonded flexible pipe has a proven track record in the offshore oil and gas industry for more than 20 years. The product is synonymous with the use of floating production systems spanning the water column and connecting subsea structures to facilitate the retrieval of hydrocarbons, provision of water injection systems and the export of processed or semi-processed fluids to main trunk pipelines or onshore. Unbonded Flexible pipe is a technically complex multi-layer structure of helically wound metallic wires and tapes and extruded thermoplastics.

In 1996 Wellstream was awarded a major contract for the supply of flexible risers and flowlines as part of the Norsk Hydro Troll Olje Gas Province Development located in 350m water depth 80km west of Bergen. The development consists of two main fields, Troll East (31/3 and 31/6) and Troll West (31/2) which together have an estimated production life in excess of 50 years, making it one of the worlds largest offshore developments. Norsk Hydro is responsible for the development and operation of the production facilities.

The scope of supply included 15-inch internal diameter, 213 barg design pressure, dynamic risers for the export of oil and gas from the platform to shore. At contract award, Wellstream was finalising the location of their European Manufacturing site, a facility which would have the capability of manufacturing unbonded flexible pipe with external diameters up to 24-inches.

The design, manufacture and qualification of a large diameter oil and gas export riser for service in the Norwegian sector of the North Sea, considered to be one of the most severe environments in the offshore industry, provided unique challenges and attributes. These risers have now been in service for over two year, following an extensive qualification programme. This paper provides an insight into the integrated approach adopted during qualification with the successful application of finite element technology to aid full-scale testing. During a full-scale test program a finite element simulation of a 15 metre long prototype pipe was performed with special emphasis on the evaluation of contact forces between the flexible pipe and a bend limiting structure. The finite element analysis program package ANSYS is chosen for this simulation due to its special feature of contact/target elements. The paper illustrates that the use of Finite Element Modelling is indeed capable of predicting the observed behaviour of prototype risers, which are subjected to a series of dynamic load cases, in a Dynamic Test Rig (DTR). Finally, the paper concludes that focus should now be given to the advantages of using finite element tools that are verified by full scale testing to reduce development costs and schedules.

 

Authors:

Zhang, Dr. W., Tuohy, J.

Justin Tuohy Publications

A Three-Dimensional Finite Element Analysis of Unburied Flexible Flowline – A Case Study

Published: June 2002 | 21st International Conference on Offshore Mechanics and Arctic Engineering | June 23, 2002 | Oslo, Norway

Abstract

Pipelines in the service of conveying hot fluid will tend to expand due to pressure and differential temperature. However, since the flowline is generally fixed at the end terminations to rigid structures or equipment, such an expansion will be restricted in longitudinal direction. This is particularly the case for the section remote from the pipe ends, and results in an axial compression in the pipe section. In many cases, a subsea flowline has to be trenched or buried for the purposes of protection and thermal insulation. Consequently, the lateral movement of a flexible flowline is greatly limited, and an upward displacement is encouraged that may become excessive. Eventually, the flowline may lift out of the trench when the uplift resistance provided by the backfill cover and self-weight of the flowline is gradually overcome by the strain energy built up in the flowline. For flexible pipe, it is this excessive upward deformation being termed as the Upheaval Buckling, which can be prevented by employing adequate downward restraint, such as sand bag / rock dump or by designing a subsea pipe route to overcome this phenomenon. In this paper a case study of the full three-dimensional finite element analysis of a trenched but unburied 6.0-inch production flowline is presented following a description of Wellstream Finite Element Method (FEM) based methodology for Upheaval Buckling analysis of flexible pipes. The effect Bending Stiffness Hysteresis and Upheaval Creep – unique to flexible pipe characteristics, is considered in addition to the general loads such as the flowline self-weight and backfill, pretension, pressure, temperature distribution and prescribed forces (either concentrated or distributed) and displacements. The effects of environmental loads, such as the action of currents that would result in scouring off the backfill, can also be addressed.
The finite element analysis program package ANSYS was chosen for this case study due to its special feature of ANSYS Parametric Design Language (APDL) and contact/target elements; and the general three-dimensional shell and solid elements were used to represent the flexible pipe and trench soil respectively.

 

Authors:

Zhang, Dr. W., Tuohy, J.

Justin Tuohy Publications

A Design Approach for a Reinforced Thermoplastic Pipe & Coupling System

Published: January 2002 | Fifth International Conference: Pipeline Rehabilitation & Maintenance | January 19 – 23, 2002 | Gulf International Convention Centre, Bahrain

Abstract

Halliflow[1], a reinforced thermoplastic pipe, has been developed for the transmission of oil and gas production fluids. Field applications are initially targeted at the onshore hydrocarbon market. However, this product is also suitable for shallow water developments and other diversified markets, which include gas transmission, water transportation, chemical process pipework and mining applications. RTP has the potential to reduce operating costs and provide an attractive life of field commercial alternative to carbon steel lines. The RTP development effort has benefited significantly from experience in the technology of unbonded flexible pipe. RTP utilises the inherent benefits of flexible pipe technology to provide a lower cost product derivative.
This paper details the RTP design methodology for polyethylene/aramid fibre based thermoplastic pipes and end fittings. For onshore applications the service life design criteria are specifically concerned with chemical resistance to internal fluids, resistance to internal pressure, tensile and bending loads, resistance to ultra violet degradation and gas permeation.

 

Authors:

Dodds, Dr. N., Southern, A., Tuohy, J., Sheldrake, Dr. T.

Justin Tuohy Publications

The Offloading Solution for Hydrocarbons in Deepwater – Offshore West Africa

Published: 2001 | The Journal of Offshore Technology

“Unbonded Flexible Pipe is a viable cost effective solution for the transportation of hydrocarbons from Floating Production, Storage and Offloading (FPSO) vessels to CALM Buoys for tanker transport to shore” – Justin Tuohy, Director, Product Strategy for Wellstream.

OFFSHORE EXPLORATION for oil and gas is being performed in even more challenging waters, with fields being developed in water depths of 2000 metres and greater. To recover hydrocarbons from these depths a number of technical challenges are presented to the designers of riser and offloading systems. Since unbonded flexible risers are an obvious solution for floating production and storage systems, being a proven technology spanning three decades, these challenges have already been overcome for the smaller diameter pipe structures. In 1999 Wellstream illustrated the technology lead by being the first manufacturer of flexible pipe to qualify 4-inch and 6-inch internal diameter products to 2000 m water depth for offshore Brazil. Continued developments will have much larger internal diameters qualified to these water depths in the near future………

Justin Tuohy Publications

An Update on Flexible Pipe Technology for Ultra-deepwater Production, Injection and Offloading Systems

Published: September 2001 | IBC Conference, “Technological Advances in Risers, Moorings & Anchorings in Deepwater Fields” | September 18 – 20, 2001 | London, England

Abstract

Offshore exploration for oil and gas is being performed in even more challenging waters, with fields being developed in water depths of 2000 metres and greater. To recover hydrocarbons from these depths a number of technical challenges are presented to the designers of riser and offloading systems. In addition, metocean characteristics and relatively low reservoir temperatures also compound the challenges.

Flexible pipe is a proven solution for conveying fluids from subsea wells to surface vessels in 2000 metres water depth. Solutions are being developed for service in up to 2500 metres. It is now the centre of focus for large diameter offloading systems in deepwater applications particularly in West Africa where significant volumes of crude oil are to be offloaded to other floating structures and tankers.

This paper discusses how Wellstream’s unbonded flexible pipe technology has overcome the challenges of floating production systems in 2000 metres water depth and how its continued development will ensure its incorporation in new pioneering solutions for ultra-deepwater riser systems.

These achievements in technology are applied to the design of large diameter offloading and export systems which are being considered for large field developments. An insight into the design and detailed analysis of the unbonded flexible pipe solutions developed by Wellstream for large diameter export riser systems is provided.

Finally, the paper concludes with an update of the comprehensive full-scale testing program currently ongoing at Wellstream’s global facilities.

Authors:

Tuohy, J., Sheldrake, Dr. T., Williamson, D.

Justin Tuohy Publications

Offloading Systems for Deepwater Developments: Unbonded Flexible Pipe Technology is a Viable Solution

Published: 2001 | Offshore Technology Conference | April 30 – May 3, 2001 | Houston, Texas, USA

Abstract

Offshore exploration for oil and gas is being performed in even more challenging waters, with fields being developed in water depths of 2000 meters and greater. To recover hydrocarbons from these depths, a number of technical challenges are presented to the designers of riser and offloading systems. Met-ocean characteristics and relatively low reservoir temperatures compound the challenges.
This paper discusses how unbonded flexible pipe technology has overcome the challenges of floating production systems in 2000 meters water depth and how its continued development enables solutions for ultra deep water riser systems. During the discussion of the status of flexible pipe technology, an overview is given to the advancements in flow
assurance technology and integrity monitoring, both of which can evolve as integral parts of the flexible pipe.
These achievements in technology are applied to the design of large diameter offloading and export systems that are being considered for large field developments where crude oil
is being offloaded to other floating structures and tankers. The paper details the design and detailed analysis of the unbonded flexible pipe solutions developed by Wellstream to overcome the deepwater challenges associated with large diameter export riser systems. Design comparisons are developed with the alternative products currently proposed.
Finally, the paper concludes with an economic appraisal of why flexible pipe systems should be considered a cost effective solution in the overall CAPEX and OPEX of deepwater field developments.

Authors:

Tuohy, J., Loper, C., Wang, Dr. D.

Justin Tuohy Publications

Unbonded Flexible Pipe Technology in Deepwater Developments for Production, and Offloading Systems

Published: March 2001 | 5th Annual Offshore West Africa Conference & Exhibition 2001 “Challenges for the Emerging Frontier” | March 21 – 23, 2001 | Abuja, NIGERIA

Abstract

Offshore exploration for oil and gas is being performed in even more challenging waters, with fields being developed in water depths of 2000 metres and greater. To recover hydrocarbons from these depths a number of technical challenges are presented to the designers of riser and off-loading systems. In addition, met-ocean characteristics and relatively low reservoir temperatures also compound the challenges of offshore West of Africa developments.

This paper discusses how Wellstream’s unbonded flexible pipe technology has overcome the challenges of floating production systems to 2000 metres water depth and how its continued development will ensure its incorporation in new pioneering solutions for ultra deep water riser systems. Specifically detailed reference is made to functional design techniques to illustrate the advantages of using hybrid unbonded flexible risers to span the water column.

The low reservoir temperatures typically found in West of Africa fields dictates that temperature management is crucial in order to minimise heat losses from the reservoir to the processing facilities to reduce the risk of wax deposition, hydrate formation and decreased flowing viscosity. Unbonded flexible pipe technology is also well placed to meet these challenges with a selection of flow assurance tools available.

The paper continues with an overview of the unbonded flexible pipe solutions developed by Wellstream to overcome the other deep water challenges associated with large diameter export riser systems. Finally, the paper concludes with an economic appraisal of why flexible pipe systems should be considered a cost effective solution in the overall CAPEX and OPEX of deep water field developments.

Authors:

Tuohy, J., Avery, A., Martin, S.

Justin Tuohy Publications

Retrieval and Reuse of Unbonded Flexible pipes – A Solution for Reducing Marginal Field Costs

Published: November 2000 | SEN 2000 “ Tieback Technology for the New Millennium” | November 28 – 29, 2000 | London, England

Abstract

Unstable oil prices over the past number of years have resulted in a slowdown of oil & gas field developments. Many of the marginal field developments are no longer viable at typical development budgets and consequently there is a need to continue to develop technology to meet the challenges whilst in parallel substantially reduce associated costs.
Since the mid 1990’s Granherne has been proactive in the drive to reduce costs of Normally Unmanned Installation (NUI) developments around the world in order to release marginal field developments and achieve facility cost reduction of 25-30%. A major element in the future oil and gas business is to find ways of releasing marginal field developments in the 10-25mmbls range characterised by small numbers of wells, Capex budgets of less than $100m and a limited field life of about 2-5 years. Here the potential reuse of facilities and pipelines becomes increasingly financially viable provided they are designed for ease of adaptation and reuse during their lifetime.
Wellstream, has always been proactive in providing cost effective solutions of flexible flowline and riser systems for field developments. Typically a flexible pipe is designed specifically to the operators requirements for a given field with a design life up to 25 or 30 years. However the field may cease production in as little as 5 years but more commonly in 10 to 15 years. In some areas of the world operators have taken advantage of this and consequently flexible pipe is relocated up to 7 times in its life in similar applications. Wellstream has assisted in evaluating the condition of the pipe structures after life of field has been reached.
Much focus has been on reducing subsea and NUI platform costs but the one remaining significant challenge is to find ways of reducing the costs of infield pipelines to host facilities. This area offers at least as much scope as that of the minimum facilities for cost reduction. One way forward is to look at the use of reelable flexible products which offer the greatest potential for reuse. Halliburton companies, Granherne and Wellstream are looking at the development of more cost effective solutions for the marginal field developments. One of the critical issues is the lack of operational data available to assess the remaining life in flexible pipes that have fulfilled the life of field requirement at their current location. Use of condition monitoring allows a service record to be maintained and ease of certification for reuse. Wellstream has been involved in the area of developing online monitoring systems since the early 1990’s and are also proactive participants in Joint Industry Programs in this area. The goal is to achieve a flexible pipeline solution which can be laid and recovered with a modular construction to allow a range of tieback distances to be accommodated. Using this approach it is possible to achieve a serial development of marginal fields around an existing host where both the surface NUI or subsea facilities and associated flowline/umbilical system can be relocated over sequential developments.
This paper discusses the significant potential for cost reduction and savings in this approach to marginal field developments. It addresses the requirement for a change in philosophy and thinking. It also requires collaborative support and co-operation from operators.

Authors:

Tuohy, J., Robinson, Dr. R.