1. Simplified models used to predict scale tendencies

2. 2) Convert to an Equilibrium equation (shorthand form shown) 1) Write the reaction 3) Rearrange to test for solids 4) Simplify 1.0 by definition

3. Step 1) Na,ppm (mol/kg)Cl, ppm (mol/kg)Ksp (@T, C / P, atm)  Na  Cl 86,000 (3.74)145,000 (4.09)38.2 (@25 / 1)0.84 2) Solve) measured calculated (symmetry)

4. Na,ppm (mol/kg)Cl, ppm (mol/kg)Ksp (@T, C / P, atm)  Na  Cl 87,250 (4.30)134,549 (4.30)35.8 (@90/70)0.74 147,250 (6.41)225,414 (6.36)36.5 (@125/200)1.11 10,800 (0.47)19,850 (0.56)41.3 (@4/100)0.69 (symmetry) S (w/o  ) S (with  ) 0.520.28 1.121.37 0.0060.003

5. CationAnion Ionppm (mol/kg)  ionppm (mol/kg)  Na + 14,500 (0.63)0.665Cl - 22,510 (0.69)0.681 K+K+ 1,234 (0.032)0.612SO 4 -2 2,142 (0.022)0.087 Ca +2 1,420 (0.035)0.253HCO 3 - 158 (4.0e -3 )0.555 Ba +2 2 (1.4e -5 )0.207CO 3 -2 (1.18e -5 )0.093 Assemble necessary variables (from software or literature) Plug in data and calculate Answer: ST=0.385 Step 1) Step 4) …

6. Assemble necessary variables (from software or literature) Plug in data and calculate Answer: ST=3.99 Step 1) Step 4) … CationAnion ppm (mol/kg)Act coef (25C, 1atm)ppm (mol/kg)Act coef (25C, 1atm) Na + 14,500 (0.63)0.665Cl - 22,510 (0.69)0.681 K+K+ 1,234 (0.032)0.612SO 4 -2 2,142 (0.022)0.087 Ca +2 1,420 (0.035)0.253HCO 3 - 158 (4.0e -3 )0.555 Ba +2 2 (1.4e -5 )0.207CO 3 -2 (1.18e -5 )0.093

7. TPCaSO4BaSO4CaCO3NaCaBaClSO4CO3 CBarKsp  5030 2.78E-051.99E-102.41E-090.6470.2160.1850.6640.1350.083 80150 1.30E-052.61E-101.63E-090.6240.1780.1640.6360.1130.068 120300 3.28E-062.37E-104.65E-100.5890.1340.1370.5960.0820.049 140460 1.61E-061.96E-102.35E-100.5680.1150.1240.5750.0660.040 170600 4.46E-071.37E-106.06E-110.5350.0880.1040.5380.0450.028 TP, barCaSO4BaSO4CaCO3 CBarSSS 5030 80150 120300 140460 170600

8. Hand calculations that include methods to predict K and 

9. K  CaCO3BaSO4CaSO4SrSO4 Langlier Saturation Index  Ryznar Stability index  Pukoris Scale Index  Stiff Davis  Oddo-Tomson 

10. * Well known, pre-computer method * Developed in 1936 to predict corrosion and CaCO 3 scale in municipal water * Results (next slide) * LSI>0 Scale forms * LSI<0 Scale dissolves * Limits * 6.5 – 9.0 pH * 4000 mg/l TDS * 95 o C pH meas = measured pH pH s = pH at saturated CaCO 3 pK 2 =HCO 3  CO 3 equilibrium const. pK sp = Calcite solubility product const. Ca +2 = Calcium conc. (mol/l) Alk = Alkalinity conc. (mol/l as HCO 3 - )

11. Start with this Rearrange Convert p to -log Multiply by -1 Take the exponent Insert CO 3 equation End with Solubility

12. LSIScaling and Corrosion TendencyTreatment +4Severe Scale FormingRequired +3Significant Scale FormingRecommended +2.0Moderate Scale-formingSuggested +0.5Slightly scaling and noncorrosive 0Balanced but corrosion possibleNo Treatment -0.5Slightly corrosive and non-scaling Mild CorrosionSuggested -2.0Moderate CorrosionRecommended -3Severe CorrosionRequired

13. Measured data Results Ionmg/lmol/l Na + 23,0001.0 Ca +2 4000.01 Cl - 35,5001.0 Alk6100.01 25C100C pK 2 10.3310.09 pK sp 8.629.28 pH7.547.47 25C100C LSI OLI (ScaleTend) 6.835 Constants and pH

14. http://www.lenntech.com/calculators/langelier/index/langelier.htm http://www.csgnetwork.com/langeliersicalc.html http://www.cleanwaterstore.com/technical/water-treatment- calculations/langlier.html These website contain an LSI calculator

15. Where: and: Ryznar (1942) refined LSI to distinguish waters with same LSI but different Ca/Alk ratios A ionic strength term is added to include salinity effects Primarily for corrosion, semi- quantitative for scale RSI is inverted: low values indicate scaling. High values indicate corrosion pK 2 and pK s are same as Langelier constants I=ionic strength M=concentration (mol/kg) z=ion charge and:

16. RSIScaling and Corrosion Tendency 4.0-5.0Heavy Scale 5.0-6.0Light Scale 6.0-7.0Little Scale or Corrosion 7.0-7.5Some Corrosion 7.5-9.0Heavy Corrosion 9.0+Corrosion Intolerable

17. http://www.lenntech.com/calculators/ryznar/index/ryzn ar.htm

18. http://corrosion-doctors.org/Corrosion-by-Water/Scaling-indices.htm Where: & Based on water buffering capacity and the maximum quantity of precipitate that can form and:

19. Stiff and Davis (1952) refined LSI to correct for high salinity of oilfield waters All the corrections are contained within a Temperature / Salinity plot

20. 0 0.5 1 1.5 2 2.5 3 3.5 4 00.40.81.21.622.42.83.23.64 Molar Ionic Strength K 0oC0oC 30 o C 50 o C 60 o C 70 o C 80 o C 90 o C 100 o C

21. Measured data Results Ionmg/lmol/lmz 2 Na + 23,0001.01 Ca +2 4000.010.04 Cl - 35,5001.01 Alk6100.01 25C100C pK 2 10.3310.09 pK sp 8.629.28 pH7.547.47 25C100C Stiff Davis OLI(ScaleTend)6.835 Constants and pH

22.  Initially developed in 1980’s  Available for CaCO 3, CaSO 4, BaSO 4, and SrSO 4  Includes gas phase for calcite scale  based on English units; F and psia Equations for Calculating CaCO 3 scaling with a gas phase present. Oddo-Tomson was a significant advancement over previous indices. Operators and service companies created spreadsheets with this model. Many are still in use.

23. J.E. Oddo, J.P. Smith, and M.B. Tomson. 1991. Analysis of and solutions to the CaCO3 and CaSO4 problems in West Indonesia. SPE22782. T in Fahrenheit, P in psia, I in mg/l TDS/58400

24. J.E. Oddo, J.P. Smith, and M.B. Tomson. 1991. Analysis of and solutions to the CaCO3 and CaSO4 problems in West Indonesia. SPE22782. T in Fahrenheit, P in psia, I in mg/l TDS/58400

25. J.E. Oddo, J.P. Smith, and M.B. Tomson. 1991. Analysis of and solutions to the CaCO3 and CaSO4 problems in West Indonesia. SPE22782. T in Fahrenheit, P in psia, I in mg/l TDS/58400

29.  Based on mild steel corrosion in Great Lakes water  Ratio of epm SO4 2- and Cl- to epm HCO 3 - +CO 3 -2  X< 0.8 - SO4 2- and Cl- will not interfere with film formation  0.8<X<1.2 - SO4 2- and Cl- may interfere with film formation. Higher corrosion rates anticipated  X>1.2 - high local corrosion rates expected epm=equivalents per million

30.  Multi Scale (Expro Petrotech)  ScaleSoftPitz (Rice University)  Downhole SAT (French Creek Software)  ScaleChem (OLI Systems)

31.  Equilibrium and steady- state  Equation of state *  Chemical Speciation *  Activity coefficient *  Phase equilibrium  Mass balance  Charge balance  Energy balance  Process simulation  non-Equilibrium and transient  Mass transfer  Phase velocity  Nucleation kinetics  Precipitation kinetics  Scale inhibition  Scale adhesion * - minimum required for accurate oilfield scale prediction

32.  Many scale prediction tools available  All based on fundamental equilibrium equations  Each have adjustments for temperature and salinity  All have some value  Low cost  Easy to use  Can calculate complex systems  Can model mixing and inhibition