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Scale Control In the Presence of Hydrate Inhibitor

Scale Control In the Presence of Hydrate Inhibitor. Outline of Presentation. Xinmin Wu – Visiting scholar, Associate Professor, Xi’an Petroleum University Case study– Scale/corrosion problem in methanol recovery plant in China, Chang Qing Gas Field - Wu

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Scale Control In the Presence of Hydrate Inhibitor

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  1. Scale Control In the Presence of Hydrate Inhibitor

  2. Outline of Presentation • Xinmin Wu – Visiting scholar, Associate Professor, Xi’an Petroleum University • Case study– Scale/corrosion problem in methanol recovery plant in China, Chang Qing Gas Field - Wu • Nucleation kinetics of calcite scale formation in the presence and absence of methanol -Tomson • Inhibition of calcite/barite scale formation by scale inhibitors -Tomson

  3. Case Study – Treatment of Methanol/Brine for Reinjection and Reuse in China Xinmin Wu Associate professor Department of Petroleum Engineering, Xi’an Shiyou (Petroleum) University, xi’an, China

  4. Chang Qing Gas Field Methanol is used to control hydrate formation. Produced water is distilled to remove methanol for re-injection and methanol is recovered for reuse.

  5. Problems • Suspended solid and emulsion Oil • Scale • Corrosion • Poor and unpredictable methanol recovery • Environmental hazard

  6. Brine Composition • TDS: 51,983-80,380 mg/L • Ca2+: 18,860 -22,784 mg/L • Mg2+: 1,124 -2049 mg/L • SO42-: 163-256 mg/L • HCO3-: 161 -272 mg/L • Ba2+, Sr2+: 0 mg/L • Fe2+: 74 – 126 mg/L • pH: 5.8-6.2 • Transmittance: 13-27% at 600 nm wavelength • Methanol: 10-20%

  7. Water Quality for Reinjection • Suspended solid: 10 mg/L • Oil:  30 mg/L • Methanol:  0.1 wt% • Sulfate reducing bacteria: 0-100/ml • Corrosion bacteria: 0-1,000/ml

  8. Brine Pretreatment • Add NaOH (200-500 mg/L) to adjust pH to 7.5-8.5. • Add H2O2 (0.1 mg/L)and dimethhyldiallyl ammonium chloride polymer (2B, 1~2 mg/L) to coagulate organics and suspended oil droplets, 30 minutes.

  9. Pretreatment Evaluation

  10. Scale/Corrosion Inhibitor • HEDP, 5 mg/L • Acrylic acid/Acrylic ester/Acrylic sulfonate copolymer (R-SO3), 6 mg/L • Benzotriazole (BTA), 2 mg/L • No precipitation observed at 50 – 100 ºC • Corrosion is less than 0.2 mm/a

  11. Methanol/Brine Treatment H2O2 NaOH 2B Sedimentation Tank Reactor Filter Heater Methanol/Brine Input HEDP BTA R-SO3 Clean brine For re-injection 96% Pure Methanol Distillation Tower

  12. Field Observation – Prior to Treatment

  13. Field Test Results

  14. NaCl SO4, Inh, MeOH NaCl Ba, Ca, MeOH Method to Study Nucleation Kinetics Batch – Barite Tube Blocking - Calcite NaCl Ca HCl MeOH Inh 0.005” ID SS A B NaCl HCO3 MeOH 25-100 C

  15. Effect of Hydrate Inhibitors - Barite Nucleation Time

  16. Prediction – Barite Nucleation Time vs. Hydrate Inh. Conc., SI, T

  17. Pred. vs. Obs. Barite Nucleation Induction Time

  18. Calcite Precipitation In the Presence/Absence of Methanol

  19. Inhibitor Efficiency In The Presence Of Hydrate Inhibitor

  20. Turbidity (NTU) Log (tind, sec) Control Barite Scale with Scale Inhibitors and Low MeOH Conc. BaSO4 = 1.1 mm, Ca= 0.09 m, 1 m NaCl, 24 C, BHPMP No MeOH 10% MeOH (w/w) 20% MeOH(w/w) SI = 2.05 SI = 2.79 SI = 3.43

  21. High MeOH Conc. 1.11 mm BaSO4, 0.09 m Ca, 24 C, 6.4 pH, 40% (w/w) MeOH, SI = 4.21 BHPMP Conc. Uncontrollable Scaling

  22. BaSO4 = 1.1 mm Ca=0.09 m, 0.98 m NaCl, pH 6.4, 24 C, SI=2.61 BaSO4 = 1.8 mm Ca=0.045 m, 1.0 m NaCl, pH 6.4, 24 C, SI=3.08 BaSO4 = 1.8 mm Ca=0.045 m, 1.0 m NaCl, pH 6.4, 24 C, SI=3.08 40% TEG (w/w) 40% MEG (w/w) 40% MEG (w/w) Turbidity (NTU) Log(tind, sec) Control Barite Scale with Scale Inhibitors and MEG, TEG

  23. Kinetics of Nucleation Inhibition Phosphonates: Polymer (Phosphinopolycarboxylic acid):

  24. MEG, TEG MeOH Barite Nucleation Inhibition - Prediction vs. Observation BHPMP Barite SI =1.6 - 3.5 MeOH = 0-20% (w/w) MEG,TEG = 0-40% (w/w) 24 C NTMP PPCA

  25. Effect of Methanol/MEG - Summary 21,932 mg/L Na+ 3,487 mg/L Ca2+ 149 mg/L Ba2+ 33,818 mg/L Cl- 104 mg/L SO42- 59,490 mg/L TDS 10,000 MCF gas 100 STB water 6.42 pH

  26. Limits of Inhibition – Ca-Phn Pseudoscale Formation 1.11 mm BaSO4, 0.09 m Ca, 1 m NaCl, 24 C, 6.4 pH, 30% (w/w) MeOH, SI=3.9 Added BHPMP Conc. ~1.8 mg/L BHPMP Remained in solution

  27. Calcite Inhibition at High Temperature Can Pseudoscale Form?Pseudoscale formation is a function of temperature, pressure, pH, TDS, Ca, Mg, Ba, Fe concentrations Ca-DTPMP ion product = 1053.6 or 1054.3 at 75 C and 100 C with 1 mg/L DTPMP; Ca-DTPMP crystalline solubility product = 1053.8 64,158 mg/L TDS, 1,600 mg/L Ca, 1200 mg/L alkalinity, pH 6.2 75 C, DTPMP 100 C, DTPMP

  28. Inhibition of Calcite Scale by DTPMP in 50% Methanol 64,158 mg/L TDS, 1,600 mg/L Ca, 1200 mg/L alkalinity, pH 6.2

  29. Conclusions • Barite and calcite scale formation at low methanol concentrations can be inhibited by common scale inhibitors at threshold level, if barite SI  3 and calcite SI  2.5. • Calcium inhibitor pseudoscale formation can occur in high Ca brine and limit the effectiveness of phosphonate type inhibitor at high concentrations. • Scale inhibition is easier in glycol containing brine than in methanol containing brine.

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