Transcript Castrol Subsea Presentation - Championing the UK subsea sector

Managing the potential gas hydrate risk in
subsea hydraulic control lines
Alan Demange, Richard Rowntree – Castrol Offshore
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)
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
If ALL elements are present…
What can we do next ?
1. Work on ensuring no gas ingress and assume no
hydrates will form
or…
2. Assume gas ingress and evaluate the actual hydrate
risk and manage it !
Hydrate formation & dissociation curve
Source: “Introduction to
Hydrates and Hydrate
Modelling”, by Beryl
Edmonds, InfoChem
Computer Services Ltd.
Focus on hydrate
dissociation curve
Evaluating & Managing the Hydrate Risk
1. Benchmarking with pure methane
13000
Results from
laboratory testing
at Heriot-Watt
University
12000
11000
P/psia
10000
Hydrate risk
Hydrate free
9000
8000
7000
6000
5000
-10
-8
-6
-4
-2
0
T/C
2
4
6
8
Evaluating & Managing the Hydrate Risk
2. What is the impact of gas impurities?
13000
12000
11000
P/psia
Effect of 4% impurities
10000
(using modelling
techniques)
9000
8000
Hydrate risk
Hydrate free
7000
6000
5000
-10
-8
-6
-4
-2
0
T/C
2
4
6
8
Evaluating & Managing the Hydrate Risk
3. The Effect of Seawater Ingress
•
The source
–
•
The impact
–
•
The subsea hydraulic coupling during installation and/or
disconnection
Dilutes the hydrate inhibition properties of the control fluid =>
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
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
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
Thank you for your attention…
Any Questions ?
www.castrolsubsea.com