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Subsea Separation:
A New Frontier for the Chemical
Engineer
Sunday Kanshio AMIChemE
Oil and Gas Engineering Centre,
Cranfield University
15th April 2015
Acknowledgement
• Petroleum Technology Development Fund, Abuja, Nigeria
• Prof Hoi Yeung- Oil and Gas Engineering Centre, Cranfield University
• IChemE Milton Keynes Committee
Presentation Outline
• Demand for Oil and Gas
• Subsea Field Development
• Subsea Separation Systems
• Academic Research and Findings
• Conclusion
Demand for Oil and Gas
“Oil is expected to remain the No. 1 energy source and demand will
increase by nearly 30 percent, driven by expanding needs for
transportation and chemicals”
ExxonMobil’s Outlook for Energy- A view to 2040; December 9, 2014
“Deepwater expenditure is expected to increase by 69%, compared to
the preceding five-year period, totalling $210 billion from 2015 to
2019”
Douglas-Westwood, London- March 9, 2015
Subsea Production Systems
• Flow assurance
• Environment regulations
• Maximising oil recovery
• Low temperature
• Water depth-Hydrostatic pressure
• Long distance
• Remoteness
• Seabed topography
Chemical Engineering
Unit Operations
Subsea
Separation
Where to go?
Courtesy: www.total.com
Challenges
Features of subsea oil and gas field
Subsea Separation
Subsea
Separation
Gas-Liquid
Separation
Oil-Water
Separation
Sand
Removal
• Hydrate prevention
• Slug flow mitigation
• Water re-injection
• Topside debottlenecking • Erosion
• Corrosion
• Reduce backpressure on wells
What is subsea separation all about?
It’s more than phase
separation!
Subsea Separation Principles
-Gravity
HORIZONTAL SEPARATOR
• Preferred for Oil-water separation
• As Subsea Slug Catcher
.
Texaco developed Highlander using SubseaSlug Catcher
• Required for slug flow mitigation• Water depth: 128 m• 13 km from existing platform• Low energy reservoir and low GOR• 35 million bbl of recoverable oil• Marginal field tieback to Tartan platform
Subsea Separation- Techniques
-Gravity
HORIZONTAL SEPARATOR
Good for Oil-water separation in shallow water
Field application: Tordis field operated by
Statoil
Tordis Subsea Separation, Boosting and
Injection Project
• Water depth : 200 m• Mature field• 25 m tieback distance to Gullfaks C Platform• Water production: 70-80%• Sand production: 500 kg/day• Bulk water separation• Multiphase boosting• Water and sand injection into dedicated well
Subsea Separation- Techniques
-Gravity
VERTICAL SEPARATOR
• Preferred for gas-liquid separation
• Easy sand removal
• Provides adequate suction head
Pazflor, Angola Courtesy of Total/FMC
Example: Pazflor, Angola block 17 operated
by Total
• First tested at Cranfield University
• Installed in 600 m-1200 m water depth
• Heavy oil –Miocene reservoirs
• Low reservoir pressure
• Gas flow freely through 6-in flowline
• Liquid boosted by Hybrid pump (18% GVF)
Subsea Separation- Techniques
-Caisson separation system
Source: FMC
Caisson separator system was
used to develop Perdido and BC-
10 field. Shell as operator
Perdido
• Tieback to Spar
• Heavy oil
• Low reservoir pressure
• Water depth : 2499 m
• Gas flow free to host facility
• ESP as boosting system
BC-10
• Tieback to FPSO
• Heavy oil
• Low reservoir pressure
• Water depth : 1499- 2000 m
• Gas flow free to host facility
• ESP as boosting system
HeavyOutlet
Inlet
Compact Separation Systems
-Centrifugal force
Technology inspired by nature…
Cyclonic separator utilizes the inertia of the incoming
stream to generate high g-force to accomplish:
⁻ Coalescence
⁻ Phase separation
Light
Outlet
Source : CALTEC
Compact Separation Systems
-Integrated systems
HI-SEP
I-SEP
Source: FMC
Marlim field operated by Petrobras was
developed by integrated compact separation
concept.
• Marginal field in 900 m water depth
• Heavy oil
• Oil and gas comingled and flow to FPSO
• Water re-injected into reservoir
CALTEC integrated two
compact separators
Research by Cranfield
University and CALTEC shows
that this system can mitigate
severe slugging in a way that
does not reduce production rate
unlike topside choking.
Design and Operational Challenges
-Can the Chemical Engineer help?
Compact separation is the future of subsea separation but there are
so many uncertainties concerning design and operation
• Fundamental understanding of multiphase flow dynamics inside
compact separators- Flow regimes, liquid holdup, phase distribution…
• Narrow operating envelope of compact separators
• Effect of upstream flow dynamics on separator performance
• Knowing when the separator is performing poorly
• Oil-water emulsion separation…Oil-in water measurement
• Discharging produced water and sand at seabed
• Predicting the performance of the separators over the field life
• Design rules for compact subsea separators My PhD is to help with the above challenges!
Academic Work
-Approach to Problem
• Prototype Gas-Liquid Pipe Cyclonic (GLPC)
separator fabricated, installed and tested.
• Installed multiphase flow measurement sensors
Trial GLPC Rig Standard GLPC Rig Tangential inlet
Wire Mesh Sensor (WMS)
ERT sensor
Results
Phase distribution prior to
Liquid Carryover
Phase distribution during
Liquid Carryover
ERT ERT
WMS
WMS
Results and Findings
Prior to liquid
carryover
During liquid
carryover
Findings
• ERT, WMS and pressure
transducers gave good
information on what is
going on inside the
separator
• Air-core has influence on
phase separation
• Mist, churn and annular
flow regime can coexist in
the gas discharge section
of the separator under
certain operating condition
of the separator
• Subsea separators does more than phase separation ; they solves flow
assurance issues, extends the life of field, and enhances assets
integrity
• Phase separation using compact separators is the future of subsea
separation
• Chemical engineers should embrace subsea separation by bringing
their understanding of unit operations to enhance the design of compact
separators
Conclusion
