TPG 4140 NTNU Natural Gas Hydrate Professor Jon Steinar Gudmundsson Department of Petroleum Engineering and Applied Geophysics Norwegian University of Science and Technology Trondheim October 22, 2013

Outline Flow assurance solids Cooling with distance in pipeline Relevance of gas hydrates Hydrate formers (smallest gas molecules) Liquid water and water vapour Gas molecules inside ice crystal cages Dissociation pressure (equilibrium) Antifreeze and Hammerschmidt’s equation Ormen Lange and Melkøya (MEG use) Glycol dehydration Gas reserves? Global warming? Cold flow?

FLOW ASSURANCE CONCERNS

Flow Assurance Flow assurance is a concept used to describe the phenomena of precipitation and deposition of solids (and multiphase flow, not discussed here) in flowlines and pipelines. Flow assurance offers technical solutions at reasonable costs without risk to installations, operators and the environment. Precipitation is not the same as deposition…

Flow Assurance Solids Asphaltene (pressure changes) Heavy, polar molecules, amorphous solid Paraffin wax (pipeline cooling) Normal paraffin C20 to C40 Gas hydrate (pipeline cooling) Methane, ethane, propane and butane Inorganic scale (fluid mixing…) Carbonates and sulphates

Hydrocarbon Solids A: Phase envelope, B: Gas hydrate, C: Paraffin wax, D: Asphaltene, E: Multiphase flow

Siljuberg 2012 (from Rønningsen 2006)

Cooling, Wellhead to Platform/Terminal

Temperature and Distance

Relevance of Natural Gas Hydrate Deposits in oil and gas pipelines!!! Gas kick in offshore drilling!! Storage and transport of gas! Cold flow in subsea pipelines? Gas resource (big claims)?? Global warming (hyd. melting)???

Mary Boatman, unknown reference

Gas Hydrate Formers

Natural Gas Hydrate Major obstacle to production of oil and gas through subsea pipelines (due to cooling). Blocks pipelines. Form when liquid water (condensed out from moist reservoir gas) and natural gas are present at “wrong” side of equilibrium line (typically 20 C and 100 bara). Water molecules are stabilized by small gas molecules such that hydrates form (physical process, not chemical reaction). Antifreeze chemical used/injected to lower the T at which hydrates form (lower “freezing” point of hydrate). Typically, 50 % antifreeze (in liquid phase) required to prevent hydrate formation. Expensive, very expensive.

Produced Fluids NCS

A: Gas reservoir, B: Oil reservoir, C: Aquifer, D: Cap rock, E: Sealing fault. A/B: Gas-oil-contact. B/C: Oil-water-contact. Gas in A saturated with water vapour (condenses out at surface). Oil formation B contains formation water (saline).

GPA (1998)

Water Vapour at 10 (Top), 20 Middle) and 30 (Bottom) MPa

Gas Molecules Trapped in Cages 12-sided, 14-sided and 16-sided polyhedra Small non-polar molecules, methane, ethane, propane and butane form gas hydrate. Carbon dioxide, hydrogen sulphide and nitrogen also form hydrate.

Gas Inside Ice Crystal Cages Skalle 2009 Carroll 2003

Structure II Gas Hydrate

Dissociation Pressure Holder et al. 1988

Equilibrium & Flow Assurance Cooling w. distance Carroll 2003

Hydrate Equilibrium (Dissociation Pressure)

Dissociation Pressure Gas Hydrate Lower line natural gas mixture; upper line with CO2 and N2

Christiansen 2012

Glykol 30-50 %

Hammerschmidt’s Equation

Properties of Alcohols, Glycols and Water

Hydrate Equilibrium Midgard Field Gas Lunde (2005): Design av flerfasesystemer for olje og gass, Tekna

Ormen Lange, Nyhamna

Ormen Lange til Nyhamna Ormen Lange, 121 km, 70 MSm3/d gass, 445 tonn/d MEG (=5,2 kg/s)

Snøhvit til Melkøya Snøhvit, 143 km, 20 MSm3/d gass, 125 tonn/d MEG (=1,5 kg/s)

Natural Gas Resource? Hydrate Zone Limited by Subsurface Temperature Senger 2009

Krey et al. 2009

Global Warming & Gas Resource William Dillon, USGS

Hedne (2012)

NTNU Cold Flow

SINTEF Cold Flow

SINTEF Cold Flow Sintef 2010

Summary Natural gas hydrate one of several flow assurance solids in oil and gas production Cooling along a pipeline gives rise to conditions for hydrate formation (free water and condensed water vapour) Methane, ethane, propane and butane plus carbon dioxide, hydrogen sulphide and nitrogen form hydrate Small gas molecules form hydrate inside an ice crystal cage at typically 20 C and 100 bar pressure (subsea systems) Antifreeze (commonly MEG) used to move equilibrium line to lower temperature such that hydrate does not form Drying (dehydration) of natural gas by TEG used to meet transport and sales specifications Gas hydrate may give problems in offshore drilling Gas hydrate considered a potential gas resource? Gas hydrate a potential contributor to global warming?

References Aske, N. (2011): Wax Control, Guest Lecture, TPG 4035 Processing of Petroleum, Department of Petroleum Engineering and Applied Geophysics, NTNU, March 7, 27 pp. Carroll, J.J. (2003): Natural Gas Hydrates: A Guide for Engineers, Gulf Professional Publishing, Elsevier Science, 270 pp. Christiansen, H.E. (2012): Rate of Hydrate Inhibitor in Long Subsea Pipelines, M.Sc. Thesis, Department of Petroleum Engineering and Applied Geophysics, Norwegian University of Science and Technology, Trondheim, ix+107 pp. Hedne, P. (2012): Subsea Processing and Transport of Hydrocarbons, Guest Lecture, TPG 4035 Processing of Petroleum, Department of Petroleum Engineering and Applied Geophysics, NTNU, January 30, 34 pp. Holder, G.D., Zetts, S.P. and Pradhan, N., 1988. Phase Behavior in Systems Containing Clathrate Hydrates, Reviews in Chemical Engineering, Vol. 5, Issue 1-4, 1-70. Krey, V. & 17 Others: (2009): Gas Hydrates: Entrance to a Methane Age or Climate Threat?, Environ. Res. Lett., Vol. 4. Lunde (2005): Design of Multiphase Systems for Oil and Gas, TEKNA Conference. Mienert, J. (2012): Signs of Instability, Nature, Vol. 490, October 25, 2 pp. Rønningsen, H.P. (2006): Transportation of Waxy Crudes in Multiphase Pipelines, Presentation in TPG 4135 Processing of Petroleum, Department of Petroleum Engineering and Applied Geophysics, Norwegian University of Science and Technology, Trondheim, 52 pp. Siljuberg, M.K. (2012): Modelling of Paraffin Wax in Oil Pipelines, M.Sc. Thesis, Department of Petroleum Engineering and Applied Geophysics, Norwegian University of Science and Technology, Trondheim, xi+68 pp. Senger, K. (2009): First-Order Estimation of In-Place Natural Gas Resources at the Nyegga Gas Hydrate Prospect, Mid-Norwegian Margin, M.Sc. Thesis, Deparment of Geology, University of Tromsø, 211 pp. Skalle, P. (2009): Pressure Control During Oil Well Drilling, BookBooN.com, 100 pp.