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 1

Flow assurance research at ASRL can involve many subjects The H 2 O( l )-hydrate( s ) boundaries for C 3 H 8 or H 2 S hydrate formation C 3 H 8 100.0 H 2 S 10.0 p / MPa 1.0 0.1 270 280 290 300 310 T / K K. I. Adeniyi and R. A. Marriott, CSM Hydrate Consortium Meeting, Golden, CO, August, 2017. 2 K. I. Adeniyi, C. E. Deering and R.A. Marriott (2017), J. Chem. Eng. Data, 62(7), 2222-2229.

Saturation, precipitation and deposition GAS FLOW, d T , d p H 2 S, CO 2 , CH 4 , S 8 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 / 10 3 m 3 ) or lbs mmcf -1 . PRECIPITATION is a release of sulfur from a saturated or supersaturated solution phase. CAUSES: CHANGE IN PRESSURE AND/OR TEMPERATURE AND/OR COMPOSITION (NUCLEATION) 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

Deposition of sulfur from a lean (dry) sour gas 50 30:10:60 H 2 S/CO 2 /CH 4 Wellhead Saturation Solubility 1.00 g Sm -3 S 8 T = 50°C p = 10 MPa 5.0 [S 8 ] satn = 0.0008 g Sm -3 40 30 p / MPa 1.0 20 0.01 0.5 0.001 0.0001 10 0.1 0 Reservoir Saturation Solubility 0 20 40 60 80 100 120 140 T = 120°C p = 38 MPa 4 [S 8 ] satn = 3.0 g Sm -3 T / °C

Deposition of sulfur from a rich sour gas 50 30:10:44.25:8:4:2:1:0.5:0.25 H 2 S/CO 2 /CH 4 /C 2 H 6 /C 3 H 8 / n -C 4 H 10 / n -C 5 H 12 / n -C 6 H 14 / n -C 7 H 16 Wellhead Saturation Solubility 1.00 g Sm -3 S 8 T = 50°C p = 10 MPa 5.0 [S 8 ] satn = 0.002 g Sm -3 40 30 p / MPa 1.0 20 0.5 0.01 10 0.001 0.1 0.0001 0 Reservoir Saturation Solubility 0 20 40 60 80 100 120 140 T = 120°C p = 38 MPa 5 [S 8 ] satn = 2.8 g Sm -3 T / °C

Where is the sulfur coming from? ¾ x H + + ¾x CaSO 4 (s) ¾ x Ca 2+ + ¾ x HSO 4 - Anhydrite solubility - + 2¼ x H 2 S + ¾ x H + ¾ x HSO 4 3 x S ° + 3 x H 2 O Disproportionation 3 x S ° + C x +1 H 2 x +4 + 2 x H 2 O 3 x H 2 S + x CO 2 + CH 4 Slow oxidation ¾ x CO 2 + ¾ x H 2 O + ¾ x Ca 2+ ¾ x CaCO 3 + 1½ x H + Carbonate formation ¾x CaSO 4 (s) + C x +1 H 2 x +4 ¾ x H 2 S + ¼ x H 2 O + ¼ x CO 2 + ¾ x CaCO 3 + CH 4 6 R. A. Marriott, P. Pirzadeh, J. J. Marrugo-Hernandez and S. Raval (2016), Can. J. Chem. 94, 406-413.

Why are we less worried about sulfur deposition in rich sour fluids? Partial oxidation reactions with sulfur require higher temperatures or are slower than those involving oxygen at the same temperature. For comparison: CH 4 + 2 O 2 CO 2 + 2H 2 O CH 4 + 2 S 2 CS 2 + 2H 2 S (800 – 1000 ° C) C x +1 H 2 x +4 + (1½ x +2) O 2 ( x +1) CO 2 + ( x +2) H 2 O C x +1 H 2 x +4 + (1½ x +2) S 2 Junk, BS, carsul ( T < 140 ° C) Recall that state sulfur occurs when the following reaction is slow on a geological timescale: 3 x S ° + C x +1 H 2 x +4 + 2 x H 2 O 3 x H 2 S + x CO 2 + CH 4 7

Conclusions regarding sulfur deposition The risk of sulfur deposition exists when a reservoir is mature (no • longer contains C 2+ ). 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. 8 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? 1984 2014 Berri → Jubail, Saudi Arabia Shah 4,000 MT day -1 12,000 MT day -1 1993 1983 Caroline → Shantz, AB Carter Creek, WY 5,100 MT day -1 (hot water) 3,000 MT day -1 9 Chemist’s attempt at drawing a sulfur pipeline

No cold spots or hot spots allowed during flow The viscosity and critical rate shear thickening of elemental sulfur. G. O. Sofekun, E. Evoy, K. L. Lesage, N. Chou and R. A. Marriott (2017), ASRL Quarterly Bulletin, July- 10 September, 2-24.

Looking deeper into the basis of our solubility model The ASRL solubility model uses robust equations for elemental sulfur phase behavior. AGM Ferreira and LQ Lobo, J. Chem. Thermodyn . 43 (2011) 95-104 RA Marriott and HH Wan, J. Chem. Thermodyn . 43 (2011) 1224-1228 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 11 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)

The reference phase diagram for elemental sulfur 2000 α -solid 1500 α - β - l p / bar 1000 liquid 500 T c β -solid gas 0 0 200 400 600 800 1000 T / °C 12 R.A. Marriott and H.H. Wan (2011), J. Chem. Thermodyn . 43 , 1224-1228.

The reference phase diagram for elemental sulfur 30000 α -solid 25000 20000 α - β - l p / psia 15000 liquid 10000 5000 T c β -solid gas 0 0 500 1000 1500 2000 T / °F 13 R.A. Marriott and H.H. Wan (2011), J. Chem. Thermodyn . 43 , 1224-1228.

Solidification of elemental sulfur 20 Liquid 1.8 g cm -3 β -solid 15 1.96 g cm -3 α -solid 2.07 g cm -3 p / bar Liquid sulfur will fill voids in 10 the dead leg, as the solid volume drops. Pressure doesn’t change. 5 Cooling 0 40 60 80 100 120 140 160 T / °C 14 R.A. Marriott and H.H. Wan (2011), J. Chem. Thermodyn . 43 , 1224-1228.

The stressed monoclinic to orthorhombic transition α -solid β -solid 2.07 g cm -3 1.96 g cm -3 monoclinic orthorhombic Crystalline semi-translucent Opaque 15 N. I. Dowling and C. Lau (2009), ASRL Quarterly Bulletin, April-June, 7-26.

The stressed monoclinic to orthorhombic transition a) 20h b) 23h Samples showing β  α transition were easy to remove from the molds (sample was liquid at 84 o C in the oven) 16 N. I. Dowling and C. Lau (2009), ASRL Quarterly Bulletin, April-June, 7-26.

Heating sulfur in a dead leg (60 to 110°C) 20 α -solid 2.07 g cm -3 β -solid 15 Liquid 1.96 g cm -3 1.8 g cm -3 p / bar 10 5 heating 0 40 60 80 100 120 140 160 T / °C 17

What does the pipeline temperature look like? 150 125 T / °C α - solid→β -solid 100 75 50 Time with constant power 18

Will there be an increase in total pressure? 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. 112°C measured at the top of the sulfur 19 N. I. Dowling and C. Lau (2009), ASRL Quarterly Bulletin, April-June, 7-26.

Heating sulfur in a dead leg beyond 110°C (the melt) 20 β -solid α -solid 1.96 g cm -3 2.07 g cm -3 15 Assuming that (a) the pipeline cannot expand or p / bar (b) sulfur is not heated 10 from one end of the dead leg to the other 5 heating 0 40 60 80 100 120 140 160 T / °C 20

Heating sulfur in a dead leg beyond 110°C (the melt) T / F 100 150 200 250 300 1600 1400 20000 Assuming that 1200 (a) the pipeline cannot 15000 expand or 1000 p / bar p / psia (b) sulfur is not heated 800 from one end of the 10000 dead leg to the other 600 400 liquid 5000 200 heating 0 0 40 60 80 100 120 140 160 21 T / °C

Heating sulfur in a dead leg beyond 110°C (the melt) T / F 100 150 200 250 300 1600 1400 20000 Assuming that the pipeline 1200 ruptures at 5000 psia 15000 1000 p / bar p / psia 800 10000 600 400 liquid 5000 200 heating 0 0 40 60 80 100 120 140 160 22 T / °C

What does the pipeline temperature look like? β -solid trying to melt 150 (no temperature halt and massive pressure rise) 140 Rupture at 5000 psia 130 T / °C 120 110 β -solid (steeper temperature rise) 100 Time with constant power 23