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 ? 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 !

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 5000 6000 7000 8000 9000 10000 11000 12000 13000 -10 -8 -6 -4 -2 2 4 6 8 T/C P/psia Results from laboratory testing at Heriot-Watt University Hydrate risk Hydrate free

Evaluating & Managing the Hydrate Risk 2. What is the impact of gas impurities? Effect of 4% impurities (using modelling techniques) 5000 6000 7000 8000 9000 10000 11000 12000 13000 -10 -8 -6 -4 -2 2 4 6 8 T/C P/psia Hydrate free Hydrate risk

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 => 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