Molecular Thermodynamics of
Brine Chemistry
Chau-Chyun Chen
Jack Maddox Distinguished Engineering Chair
Department of Chemical Engineering
Texas Tech University
Presented at the UpTec Workshop, May 16, 2014
Slide 1
Slide 2
http://www.nobelprize.org/nobel_prizes/chemistry/laureates/1901/
Composition of Oilfield Produced Water
Slide 3
Igunnu and Chen, Int J Low Carbon Tech., 2012, 0, 1-21; Lou et al., 2014
Composition of Oilfield Produced Water
Cations
Anions
Slide 4
Igunnu and Chen, Int J Low Carbon Tech., 2012, 0, 1-21; Lou et al., 2014
Slide 5
Lou et al., 2014
Slide 6
Lou et al., 2014
Slide 7
Lou et al., 2014
Accurate thermodynamic model is the scientific foundation of process simulation
Slide 8
Accurate thermodynamic model is the scientific foundation of process simulation
Slide 9
Composition of Brines/Injection
Water/Formation Water
Slide 10
Fluid Phase Equilibria, 2014, 373, 43-54
Slide 11
Fluid Phase Equilibria, 2014, 373, 43-54
Important Salts in Hexary Oceanic Salt
Systems (Na+/K+/Mg2+/Ca2+,Cl-/SO42-)
Slide 12
Pure Appl Chem, 2001, 73, 831-844
Slide 13
Pitzer’s Ion-Interaction Model
Slide 14
Slide 15
Pure & Applied Chemistry, 2001, 73, 831-844
Slide 16
Pitzer Model for Hexary Oceanic Salt
Systems (Na+/K+/Mg2+/Ca2+,Cl-/SO42-)
o 3 parameters per binary and additional 2 per ternary
o 8 binary and 16 ternary systems
o 56 isothermal parameters and additional 2 for 2-2 valent
electrolytes (MgSO4 and CaSO4) -> 58 parameters
o Parameters & code available in PHREEQC, ChemApp,
GEMS, MINEQL+, etc.) for room temperature applications
 To cover 0 to 200 °C, up to 8 temperature coefficients are
necessary for each Pitzer parameter -> 464 coefficients
 Predictive power limited at ionic strength > 6 molal
 Need models with smaller number of parameters -> one
general approach is NRTL+xDH
Slide 17
Pure Appl Chem, 2011, 83, 1015-1030
Slide 18
Electrolyte NRTL Model
G ex  G ex ,lc  G ex , PDH
  X iGim im 
  X iGic ic 
  X iGia ia 
 i

 ic

 ia

  nm 
   zc nc 
   za na 

RT
X
G
X
G
X
G
m
  i im  c
  i ic  a
  i ia 
 i

 ic

 ia

G ex ,lc
4 A I x  1  I x 2 
G ex , PDH

ln 
0 1/ 2 
nRT

1


(
I
x)


1
1
ln  i 
RT
 G ex 


 n 
 i T , P , n j i
i, j  m, c, a
Slide 19
I&ECR, 2009, 48, 7788-7797
Development of TTU Thermodynamic
Model for Brines & Produced Water
 Based on symmetric electrolyte NRTL model
 An industry standard and a comprehensive thermodynamic
model capable of handling aqueous electrolytes, nonaqueous
electrolytes, nonelectrolytes, ionic liquids, etc.
 Successfully used to model scale formation in oil reservoirs
during water injection, CO2 capture with amines, and CO2
solubility in saline water
 Cover temperatures up to 200 °C and salt concentrations up to
saturation
 Code available in Aspen process simulator
Slide 20
eNRTL Model for Hexary Oceanic Salt
Systems (Na+/K+/Mg2+/Ca2+,Cl-/SO42-)




2 parameters per binary and additional 2 per ternary
8 binary and 16 ternary systems
48 isothermal parameters
To cover 0 to 200 °C, up to 3 temperature coefficients
are necessary for each eNRTL parameter -> 144
parameters (vs. 464 for Pitzer)
 Predictive up to saturation
Slide 21
Pure Appl Chem, 2011, 83, 1015-1030
Slide 22
Model Development: KCl-H2O Binary
Slide 23
Model Development: KCl-NaCl-H2O
Ternary
Slide 24
NaCl-Na2SO4 at 25 °C
Slide 25
NaCl-MgCl2 at 25 °C
Slide 26
MgCl2-MgSO4 at 25 °C
Slide 27
MgCl2-MgSO4 at 75 °C
Slide 28
MgSO4-Na2SO4 at 25 °C
Slide 29
Astrakhanite: MgSO4.Na2SO4.4H2O
MgSO4-Na2SO4 at 75 °C
Slide 30
Loweite: 2MgSO4.2Na2SO4.5H2O; Vanthoffite: MgSO4.3Na2SO4
Next Steps
 Molecular thermodynamic model for the hexary
oceanic salt system within ~12 months
 Molecular thermodynamic model for hydraulic
fracturing (adding Ba2+/Sr2+, HCO3-,) within ~24
months
 TTU models should support process modeling and
simulation of produced water treatment processes and
mixing of brines/produced water
 TTU models should have applications in many other
fields
Slide 31