2 Executive Summary
Subsea processing could be defined as any means of treatment (e.g. liquid/gas separation) and handling (e.g. boosting) of the produced fluid, performed at the seafloor level.
The following processes and technologies have been given much attention and were developed through last years:
Raw Water Separation
Gas/Liquid Separation
Gas Compression
Subsea Boosting / Pumping
Subsea Chemical Storage and Injection
Raw water separation (Chapter 3, Water / Hydrocarbon Separation) has been developed and the first application (pilot) has been put in operation on Norsk Hydro's Troll Pilot. Further optimised solutions have been developed and qualified since this application, in particular concerning sand handling systems (which was not a challenge on Troll Pilot but is foreseen to be on most subsea applications, e.g. Tordis SSBI). Produced water is still separated on Tordis but is not anymore re-injected in well injection tree.
Marlim SSAO is in operation with separation and re-injection of produced water and exportation of gas and oil as multiphase flow.
Developments are on-going to decrease the level of Oil-In-Water with Subsea Compact Flotation Unit and subsea Compact Electrostatic Coalescer.
Seawater subsea treatment and injection technology is described in Chapter 4, Seabed Water Treatment and Injection. Among the 3 fields where raw water injection was installed, Columba East, Tyrihans and Albacora, only Albacora l’Este Field is still operating.
NOV has progressed with the qualification of the SeaBox, a subsea unit for seawater disinfection for raw water injection or re-treatment to further filtration. Solutions for subsea seawater desulfatation are developed by NOV, BHGE and SAIPEM / TOTAL / VEOLIA. SPRING concept developed by SAIPEM / TOTAL and Veolia should be ready for first deployment in 2020.
The gas / liquid separation (Chapter 5, Gas / Liquid Separation), combined with a liquid boosting system, is applied on field by:
This technology is now mature enough and considered for new field development.
The gas compression (Chapter 6, Gas Compression and Subsea Boosting) is now a field proven technology. Extensive studies brought this technology up to field application level, e.g. by Statoil for an installation on the Asgard field in 2015 and Gullfaks in 2015.
The subsea pumping is the most mature technology, including both liquid pumps (ESP, refer to Chapter 7, Submersible Pumps) and multiphase pumps (Chapter 8, Multiphase Pumping Systems). Several field applications have been performed, including:
Subsea processing is an emerging tool which aims at both (1) developing new fields with some additional economical incentives and (2) increasing the life and recovering rate of mature fields. The general benefits of subsea processing are the followings:
Increased or accelerated production
Increased recovery rate and extended production
Marginal field production is enabled (e.g. long tie-back or very deepwater fields)
Improved flow management (e.g. gas separation avoids slug appearance, water separation acts as hydrate prevention strategy, etc.)
Reduced CAPEX in some cases, by decreasing pipeline and / or topside costs
The following Table 2.1, “Subsea Process Technology Status Summary” summarises the status of the different technologies.
Table 2.1 - Subsea Process Technology Status Summary
Process | Status | Experience | Main Manufacturers / Contractors |
Water / Hydrocarbon Separation | Mature (Field Application) | Subsea experience: Troll Pilot (Norsk Hydro) Field Application: Tordis SSBI (2007 - Statoil) Marlim (2013) |
|
Seabed Water Treatment | Mature (Field Application) |
|
|
Gas / Liquid Separation | Mature (Field Application) | Field Application: VASPS => Marimba (Petrobras) Caisson separation => installed on BC-10, Perdido. Vertical gravitational separator => Pazflor project. |
|
Gas Compression | Mature (Field Application) | Ormen Lange Gas Compression Pilot (GE and AkerSolutions) Asgard with subsea gas compression in 2015 (MAN compressor and AkerSolutions pump) Gullfaks Subsea Wet Gas Compression System (OneSubsea) started in 2015 |
|
Boosting: ESP | Mature (Field Application) | Numerous field applications, incl. VASPS (Petrobras - dummy well) and downhole applications. |
|
Boosting: Multiphase Pump | Mature (Field Application) | Several field applications, incl.: Ceiba (Amerada Hess), Tordis SSBI (2007 - Statoil), Lyell (CNR), King (2007 – BP) GirRi, CLOV, Moho Phase 1bis |
|
Typical dimensions and weight of the different components of subsea processing systems are summarised in the following table.
Modules | Weight (Tonnes) | Dimensions (m) | |||
Length | Width | Height | |||
'Typical' Separation and Boosting System | Foundation | 50 – 100 | 6m Diameter | 15 | |
(soil type dependent) | |||||
Manifold | 45 – 55 | 15 | 7.5 | 11 | |
Separator | 80 – 150 | 12.5 | 4 | 5 | |
Pump | 35 – 50 | 3 | 3 | 6.5 | |
Valves and Piping | 20 – 40 | - | - | - | |
Process Control | 2 | 1.5 | 1 | 3 | |
Overall | ~ 400 | ||||
Tordis SSBI (1) | Separator | 170 | 20 | 2.3 | |
Overall | 1250 | 40 x 25 x 19 | |||
Gas Compression (2) | Motorcompressor (motor cooler not included) | 31 | 2 x 2 | 5 | |
Overall, incl. 4 compression trains, electrical equipment and auxiliaries (scrubbers & pumps). | 850 | 30 x 30 | 7 | ||
Electrical Subsea Pump | (3) | Diameter up to 30” | Up to 40m | ||
(1200 HP ESP) | (1200 HP ESP) | ||||
Multiphase Pumping System | Pump | 50 | 6.5 | 3 | 4.5 |
Inline Manifold | 60 | 9.5 | 8.5 | 10.5 | |
Control | 2 | 1 | 1 | 1.5 | |
Overall | ~ 170 | ||||
(1): The Tordis unit is the biggest separation & boosting system expected at the time of the report.
The design values are as follows (see Section 3.5, “Tordis SSBI Project”):
Water Depth: 200m
Flow rate: extraction of up to 150,000b/d of water from the 200,000b/d wellstream
Operating pressure: 25-40 bar (200 bar design pressure)
(2): Technology in development – No consolidated data available.
Values from Ormen Lange project, to be located at a water depth of 860m
(3): No Data available
Typical Modules Weight and Size
