Managing the potential gas hydrate risk in subsea hydraulic control lines Alan Demange, Richard Rown

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Managing the potential gas hydrate risk in subsea
hydraulic control linesAlan Demange, Richard
Rowntree Castrol Offshore
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Introduction to Hydrates

• What are they ?
• Crystalline solid compounds (water light gases)
• How do they form ?
• High pressure
• Low temperature
• Presence of water
• Gas (e.g. C-1, methane)

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Introduction to Hydrates

• Can they be found in another part of the Subsea
  Production System ?
• High pressure conditions in hydraulic HP control
  lines
• Low temperature seabed temperatures
• Presence of water from the control fluid !
• Gas potential migration through SSSV

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If ALL elements are present

• What can we do next ?
• Work on ensuring no gas ingress and assume no
  hydrates will form
• or
• Assume gas ingress and evaluate the actual
  hydrate risk and manage it !

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Hydrate formation dissociation curve

• Source Introduction to Hydrates and Hydrate
  Modelling, by Beryl Edmonds, InfoChem Computer
  Services Ltd.

Focus on hydrate dissociation curve
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Evaluating Managing the Hydrate Risk

• 1. Benchmarking with pure methane

Results from laboratory testing at Heriot-Watt
University
Hydrate free
Hydrate risk
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Evaluating Managing the Hydrate Risk

• 2. What is the impact of gas impurities?

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Evaluating Managing the Hydrate Risk

• 3. The Effect of Seawater Ingress
• The source
• The subsea hydraulic coupling during installation
  and/or disconnection
• The impact
• Dilutes the hydrate inhibition properties of the
  control fluid gt increases the hydrates risk
• Solutions
• Take seawater ingress into consideration in risk
  assessment
• Hydraulic coupling selection
• Develop an installation procedure to reduce
  overall
• seawater content

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Evaluating Managing the Hydrate Risk

• 4. The role of the control fluid
• Measure the hydrate inhibition properties of the
  control fluid
• Ensure consistent product quality consistent
  properties
• For more extreme developments
• Deeper water, Gas projects, X HP/HT developments
• Products with enhanced hydrate inhibition
  properties are available for pressure
  requirements up to 25k psi

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Evaluating Managing the Hydrate Risk

• 5. Summary
• Compare control fluid hydrate dissociation curve
  versus expected system pressures and temperatures
• Clarify pressure data especially w.r.t to
  hydrostatic head and system design v actual
  pressures.
• Requires good interfacing between SPS team and
  Completions
• Remember to consider the impact of gas impurities
  sea water ingress!
• If system is in the risk zone consider control
  fluid with enhanced hydrate inhibition properties

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• Thank you for your attention
• Any Questions ?
• www.castrolsubsea.com