FLOW ASSURANCE FOR SULFUR IN SOUR GAS PRODUCTION Robert A. Marriott - - PowerPoint PPT Presentation

FLOW ASSURANCE FOR SULFUR IN SOUR GAS PRODUCTION

Robert A. Marriott

MESPON, Abu Dhabi Oct 17, 2017

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Flow assurance research at ASRL can involve many subjects

The H2O(l)-hydrate(s) boundaries for C3H8 or H2S hydrate formation

• K. I. Adeniyi and R. A. Marriott, CSM Hydrate Consortium Meeting, Golden, CO, August, 2017.
• K. I. Adeniyi, C. E. Deering and R.A. Marriott (2017), J. Chem. Eng. Data, 62(7), 2222-2229.

0.1 1.0 10.0 100.0 270 280 290 300 310 C3H8 T / K p / MPa H2S

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DEPOSITION is the adherence of sulfur to the surface of the reservoir rock, wellbore, valves, fittings, flow lines, vessels, etc. INDUCED BY: SURFACE ADSORPTION, CHANGES IN GAS VELOCITY (speed or direction), FLOW PATH RESTRICTIONS, FILTERS, LIQUIDS IN PIPES AND VESSELS

GAS FLOW, dT, dp

H2S, CO2, CH4, S8

PRECIPITATION is a release of sulfur from a saturated or supersaturated solution phase. CAUSES: CHANGE IN PRESSURE AND/OR TEMPERATURE AND/OR COMPOSITION (NUCLEATION) SULFUR SATURATION POINT (carrying capacity) is the equilibrium condition where an sour gas solution contains the maximum quantity of dissolved sulfur. Industrially, saturation is expressed as g m-3 (kg / 103 m3) or lbs mmcf-1.

Saturation, precipitation and deposition

10 20 30 40 50 20 40 60 80 100 120 140

0.0001 0.001 0.01 0.1 0.5 1.0 5.0

30:10:60 H2S/CO2/CH4 1.00 g Sm-3 S8 p / MPa T / °C Wellhead Saturation Solubility T = 50°C p = 10 MPa [S8]satn = 0.0008 g Sm-3 Reservoir Saturation Solubility T = 120°C p = 38 MPa [S8]satn = 3.0 g Sm-3

Deposition of sulfur from a lean (dry) sour gas

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10 20 30 40 50 20 40 60 80 100 120 140

0.0001 0.001 0.01 0.1 0.5 1.0 5.0

p / MPa T / °C Wellhead Saturation Solubility T = 50°C p = 10 MPa [S8]satn = 0.002 g Sm-3 Reservoir Saturation Solubility T = 120°C p = 38 MPa [S8]satn = 2.8 g Sm-3

Deposition of sulfur from a rich sour gas

30:10:44.25:8:4:2:1:0.5:0.25 H2S/CO2/CH4/C2H6/C3H8/n-C4H10/n-C5H12/n-C6H14/n-C7H16 1.00 g Sm-3 S8

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Where is the sulfur coming from?

¾x Ca2+ + ¾x HSO4

• Anhydrite solubility

3x S° + 3x H2O Disproportionation 3x H2S + x CO2 + CH4 Slow oxidation ¾x CaCO3 + 1½x H+ Carbonate formation ¾x H2S + ¼x H2O + ¼x CO2 + ¾x CaCO3 + CH4 ¾x H+ + ¾x CaSO4(s) ¾x HSO4

• + 2¼x H2S + ¾x H+

3x S° + Cx+1H2x+4 + 2x H2O ¾x CO2 + ¾x H2O + ¾x Ca2+ ¾x CaSO4(s) + Cx+1H2x+4

• R. A. Marriott, P. Pirzadeh, J. J. Marrugo-Hernandez and S. Raval (2016), Can. J. Chem. 94, 406-413.

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Partial oxidation reactions with sulfur require higher temperatures or are slower than those involving oxygen at the same temperature. For comparison: Recall that state sulfur occurs when the following reaction is slow on a geological timescale: CO2 + 2H2O CS2 + 2H2S (800 – 1000°C) (x+1) CO2 + (x+2) H2O Junk, BS, carsul (T < 140°C) 3x H2S + x CO2 + CH4

Why are we less worried about sulfur deposition in rich sour fluids?

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CH4 + 2 O2 CH4 + 2 S2 Cx+1H2x+4 + (1½x+2) O2 Cx+1H2x+4 + (1½x+2) S2 3x S° + Cx+1H2x+4 + 2x H2O

Conclusions regarding sulfur deposition

• The risk of sulfur deposition exists when a reservoir is mature (no

longer contains C2+). This is chemical and not due to solubility. We can sample liquids during from flow test separator.

• For lean (dry) sour gases, the only way to obtain the sulfur content is

(i) calculate by assuming saturation in the reservoir or (ii) measure the sulfur content at bottomhole.

• If the fluid is know to have mercury, there will be no elemental sulfur

(if a fluid has elemental sulfur, there will be no elemental mercury).

• Once the sulfur content is known, saturation can be calculated along

the production conditions to estimate where and how much sulfur can deposit (design for solvent).

• If sulfur deposition occurs with rich reservoir fluid or after the amine

system, look for oxygen ingress.

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• F. Bernard, P.M. Davis, R.A. Marriott (2017), ASRL Quarterly Bulletin, July-September, 25-31.

What happens when we solidify and re-melt sulfur?

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Chemist’s attempt at drawing a sulfur pipeline 1983 Carter Creek, WY 3,000 MT day-1 1984 Berri → Jubail, Saudi Arabia 4,000 MT day-1 1993 Caroline → Shantz, AB 5,100 MT day-1 (hot water) 2014 Shah 12,000 MT day-1

No cold spots or hot spots allowed during flow

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• G. O. Sofekun, E. Evoy, K. L. Lesage, N. Chou and R. A. Marriott (2017), ASRL Quarterly Bulletin, July-

September, 2-24.

The viscosity and critical rate shear thickening of elemental sulfur.

Looking deeper into the basis of our solubility model

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The ASRL solubility model uses robust equations for elemental sulfur phase behavior.

Recommended thermodynamic conditions for the low-pressure phase diagram of elemental sulfur Condition T / K T / °C T / °F p / Pa p / psia Triple point (α-β-g) 368.39 95.24 203.43 0.4868 0.00007060 Triple point (α-β-l) 419.06 145.91 294.64 124,360,000 18,036 Triple point (β-l-g) 388.326 115.176 239.317 2.4437 0.00035443 Natural melt (β-l) 388.348 115.198 239.356 101,325 14.696

Note that the ‘observed’ melting point is normally T = 393.5 ± 0.5 K (120.0 ± 0.5 °C or 248.1 ± 0.9 °F)

AGM Ferreira and LQ Lobo, J. Chem.

• Thermodyn. 43 (2011) 95-104

RA Marriott and HH Wan, J. Chem.

• Thermodyn. 43 (2011) 1224-1228

500 1000 1500 2000 200 400 600 800 1000

The reference phase diagram for elemental sulfur

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p / bar T / °C α-solid β-solid α-β-l liquid gas Tc

R.A. Marriott and H.H. Wan (2011), J. Chem. Thermodyn. 43, 1224-1228.

5000 10000 15000 20000 25000 30000 500 1000 1500 2000

The reference phase diagram for elemental sulfur

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p / psia T / °F α-solid β-solid α-β-l liquid gas Tc

R.A. Marriott and H.H. Wan (2011), J. Chem. Thermodyn. 43, 1224-1228.

5 10 15 20 40 60 80 100 120 140 160

Solidification of elemental sulfur

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p / bar T / °C α-solid 2.07 g cm-3 β-solid 1.96 g cm-3 Liquid 1.8 g cm-3

R.A. Marriott and H.H. Wan (2011), J. Chem. Thermodyn. 43, 1224-1228.

Cooling Liquid sulfur will fill voids in the dead leg, as the solid volume drops. Pressure doesn’t change.

The stressed monoclinic to orthorhombic transition

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α-solid 2.07 g cm-3 β-solid 1.96 g cm-3 Crystalline semi-translucent Opaque monoclinic

• rthorhombic
• N. I. Dowling and C. Lau (2009), ASRL Quarterly Bulletin, April-June, 7-26.

The stressed monoclinic to orthorhombic transition

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• N. I. Dowling and C. Lau (2009), ASRL Quarterly Bulletin, April-June, 7-26.

a) 20h b) 23h Samples showing β  α transition were easy to remove from the molds

(sample was liquid at 84oC in the oven)

5 10 15 20 40 60 80 100 120 140 160

Heating sulfur in a dead leg (60 to 110°C)

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p / bar T / °C α-solid 2.07 g cm-3 β-solid 1.96 g cm-3 Liquid 1.8 g cm-3 heating

50 75 100 125 150

What does the pipeline temperature look like?

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T / °C Time with constant power α-solid→β-solid

Will there be an increase in total pressure?

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112°C measured at the top of the sulfur Assuming that β-sulfur did not flow upon changing to α-sulfur, the α-sulfur would occupy less space and there may not be any change in total pressure. There may be local pressure/stress.

• N. I. Dowling and C. Lau (2009), ASRL Quarterly Bulletin, April-June, 7-26.

5 10 15 20 40 60 80 100 120 140 160

Heating sulfur in a dead leg beyond 110°C (the melt)

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p / bar T / °C α-solid 2.07 g cm-3 β-solid 1.96 g cm-3 heating Assuming that (a) the pipeline cannot expand or (b) sulfur is not heated from one end of the dead leg to the other

200 400 600 800 1000 1200 1400 1600 40 60 80 100 120 140 160 5000 10000 15000 20000 100 150 200 250 300

Heating sulfur in a dead leg beyond 110°C (the melt)

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p / bar T / °C liquid heating p / psia T / F Assuming that (a) the pipeline cannot expand or (b) sulfur is not heated from one end of the dead leg to the other

200 400 600 800 1000 1200 1400 1600 40 60 80 100 120 140 160 5000 10000 15000 20000 100 150 200 250 300

Heating sulfur in a dead leg beyond 110°C (the melt)

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p / bar T / °C liquid heating p / psia T / F Assuming that the pipeline ruptures at 5000 psia

100 110 120 130 140 150

What does the pipeline temperature look like?

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T / °C Time with constant power β-solid (steeper temperature rise) β-solid trying to melt (no temperature halt and massive pressure rise) Rupture at 5000 psia

Conclusions regarding the freezing and melting of sulfur in a pipeline

• Sulfur’s thermodynamic (natural) melting point is consistent with the

solidification point, assuming no super-cooling.

• Upon solidification, liquid sulfur fills void space when the higher

density solid forms. This will fill a dead-leg with high-density solid.

• Upon cooling, the monoclinic (α-solid) to orthorhombic (β-solid)

transition, stresses large crystals and causes many smaller crystallites. This causes sulfur to become friable, unless there is sufficient polymeric sulfur to help bind the crystallites.

• The temperature along the pipeline can show important information

regarding the transitions and pipeline integrity.

• Heating from one end of the dead leg to the another may avoid

catastrophic pressure increase.

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MIA: Peter Clark and Connor Deering

ASRL 2017

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Aecom Technology Corporation Air Liquide Global E&C Solutions / Lurgi Ametek Process & Analytical Instruments/Controls Southeast Arkema AXENS Black & Veatch Corporation BP Brimstone STS Ltd. Bryan Research & Engineering, Inc. Canadian Energy Services/PureChem Services ConocoPhillips Company CB&I Chevron Energy Technology Company Denbury Resources Inc. Devco Duiker CE E.I. du Pont Canada Company / MECS Inc. Enersul Inc. Euro Support BV ExxonMobil Upstream Research Company Flint Hills Resources HEC Technologies Hexion Inc. HPPE LLC Husky Energy Inc. Industrial Ceramics Limited Jacobs Canada lnc. / Jacobs Nederland B.V. KT – Kinetics Technology S.p.A. Linde Gas and Engineering (BOC) Nova Chemicals OMV Exploration and Production GmbH Optimized Gas Treating, Inc. Ortloff Engineers, Ltd. Petro China Southwest Oil and Gas Field Company/RINGT Petroleum Institute / Abu Dhabi National Oil Company (ADNOC) Phillips 66 Company Porocel Industries, LLC Porter McGuffie, Inc. Prosernat Saudi Arabian Oil Company (Saudi Aramco) Secure Energy Services SemCAMS ULC Shell Canada Energy SiiRTEC Nigi S.p.A. Sulfur Recovery Engineering (SRE) Sulphur Experts Inc. TechnipFMC Total S.A. TransCanada Pipelines Ltd. UniverSUL Consulting WorleyParsons

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