Composition & PVT (Fluid properties as a function of Pressure, Volume and Temperature) Statoil module Field development Magnus Nordsveen
Compositions and PVT important for: Value and market Field development solution Reservoir (gas, oil, heavy oil) Wells and flowlines Processing (subsea, platform, onshore plant) Pipeline transport to shore (gas, condensate, oil) Offloading to ship (condensate and oil)
Compositions and PVT important for: Wells and flowlines Pressure and temperature drop Phase transfer (gas/oil split) Densities Viscosities Surface tension Conductivities Heat capacity Wax, hydrates, Asphaltenes
Content Compositions Phase transfer, phase envelops and reservoir types Water, Hydrates and Ice Comp Mole% N2 0.95 CO2 0.6 H20 0.35 C1 95 C2 2.86 C3 0.15 ic4 0.22 nc4 0.04 ic5 0.1 nc5 0.03 C6 0.07 C7 0.1 C8 0.08 C9 0.03 C10+ 0.13
Compositions of gas and oil C C C C C Comp Mole% N2 0.95 CO2 0.6 H20 0.35 C1 95 C2 2.86 C3 0.15 ic4 0.22 nc4 0.04 ic5 0.1 nc5 0.03 C6 0.07 C7 0.1 C8 0.08 C9 0.03 C10+ 0.13
Compositions of gas and oil Isomers: Different structure configurations of same carbon numbers 75 isomers of decane C 10 H 22 (single bounds) 366319 isomers of C 20 H 42 (single bounds) Complexity further increased by double bounds, triple bounds, rings, other atoms H C H H C H
Normal, paraffinic oil
Lab analysis of samples Gas Chromatography and distillation Mass spectrometry (not standard) Viscosity measurements Boiling point Wax appearance temperature, wax deposition, etc. Hydrate equilibrium temperature (HET)
Characterisation of fluids based on composition Thousands of components from methane to large polycyclic compounds Carbon numbers from 1 to at least 100 (for heavy oils probably about 200) Molecular weights range from 16 g/mole to several thousands g/mole Comp Mole% N2 0.95 CO2 0.6 H20 0.35 C1 95 C2 2.86 C3 0.15 ic4 0.22 nc4 0.04 ic5 0.1 nc5 0.03 C6 0.07 C7 0.1 C8 0.08 C9 0.03 C10+ 0.13
Low carbon number components: Possible to measure with reasonable accuracy Known properties Higher carbon number components: consists of many variations with different properties cannot measure individual components Characterization: Lump C10 and higher into C10+ Comp Mole% N2 0.95 CO2 0.6 H20 0.35 C1 95 C2 2.86 C3 0.15 ic4 0.22 nc4 0.04 ic5 0.1 nc5 0.03 C6 0.07 C7 0.1 C8 0.08 C9 0.03 C10+ 0.13
Content Compositions Phase transfer, phase envelops and reservoir types Water, Hydrates and Ice
Phase diagram for a single component P Dense phase Critical point Solid Liquid Gas Trippel point T
Phase diagram for C3 (99%) and nc5 (1%)
Phase diagram for C3 (50%) and nc5 (50%)
Phase envelope of a gas condensate reservoir
C Gas Condensate C Oil Heavy oil C C = Critical point
Holdup: b liquid volume fraction in the cross section Oil density: r Gas density: r Effective density: r br b r Gravitational pressure drop: dpgrav = r (g: gravity, H: Height) Total pressure drop: dp = dp + dp
Holdup Effective density [kg/m3] Height [m] dpgrav [bar] dpfric* [bar] 0 80 2000 16?? 0.5 440 2000 86?? 1 800 2000 157?? *need more detailed calculations (will be addressed later in course) dp* [bar]
Equations of state (EOS) & Phase envelope An equation correlating P (pressure), V (volume) and T (temperature) is called an equation of state Ideal gas law: PV = nrt <=> P (good approx. for P < 4 bar) n: moles, R: gas constant, : molar volume RT v Van der Waals cubic EOS: P RT v b a 2 v a: is a measure for the attraction between the particles b: is the volume excluded from by the particles
Equations of state (EOS) & Phase envelope
In the oil industry we typically use software packages to characterize the fluid based on a measured composition In Statoil we use PVTSim from Calsep Ref: Phase Behavior of Petroleum Reservoir Fluids (Book), Karen Schou Pedersen and Peter L. Christensen, 2006.
Content Compositions Phase transfer, phase envelops and reservoir types Water, Hydrates and Ice
Water in hydrocarbon reservoirs - flowlines In reservoir: Separate liquid water layer Water vapour in gas layer In wells/flowlines: Condensed water in gas condensate flowlines Produced water from oil reservoirs Liquid water and hydrocarbons are essentially immiscible in each other However, liquid water and oil can form emulsions/dispersions With water, oil and gas present in flowlines, there are generally 2 liquid fields and 1 gas field
Gas hydrates (Burning snow ) Ice/snow crystals of water and gas molecules Can cause pipeline blockage
Gas hydrates Hydrate formation requires: Access to small molecules C 1, C 2, C 3, I-C 4, CO 2, H 2 S, N 2 Gas molecules stabilise cages made of water molecules. Access to free water Condensed water is good enough High enough pressure Hydrates can be stable at 10-15 bar Low enough temperature But still good summer temperature
Gas hydrates Gas molecules stabilise cages made of water molecules.
Pressure Trykk (bar) (bara) Hydrate formation domain 400 350 300 Chemicals move the hydrate curve 250 200 Hydrate domain 150 100 50 No hydrates Normal operational domain 0 0 5 10 15 20 25 30 Temperature ( C)
Hydrate formation curves Mono Ethylene Glycol (MEG) as inhibitor defroster Chemicals move the hydrate curve No hydrates Normal operational domain
Safety Hazards of Moving Hydrate Plugs (From Chevron Canada Resources, 1992) A hydrate plug moves down a flowline at very high velocites. Closed Valve If the velocity is high enough, the momentum of the plug can cause pressures large enough to rupture the flowline. Closed Valve
Ice In deep waters the sea bed temperature can be lower than 0 C Ormen Lange: -1 C at sea bed Large pressure drop can give large temperature drop due to the Joule Thompson effect Over chokes In long gas condensate flowlines
Temperature [oc] Ice formation temperature as function of pressure 0-0.5-1 Condensed water -1.5-2 -2.5 0 50 100 150 200 250 300 Pressure [bar]
Ice formation temperature as function of MEG 0-0.5-1 o C Temp Water -1.5-2 Ice -2.5-3 -3.5-4 0 1 2 3 4 5 6 7 8 9 10 wt% MEG in water+meg MEG wt%
Ice Normally hydrates are formed before ice Inhibition to avoid hydrates will also hinders ice However, in depressurized flowlines (hydrates will not form) ice may form Statoil has not experienced ice formation in flowlines
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