(74a) Development of a Comprehensive Molecular Thermodynamic Model for High Salinity Produced Water in Oil and Gas Productions

Development of a Comprehensive Molecular Thermodynamic Model
for High Salinity Produced Water in Oil and Gas Productions

Chau-Chyun Chen

Department of Chemical
Engineering, Texas Tech University, Lubbock, TX 79409-3121, USA

Abstract

Managing produced water in the rapidly
developing shale gas industry is a major challenge for protecting the
environment [Shaffer et al., Environ.
Sci. Technol. 2013, 47, 9569-9583]. Desalination for reuse of produced
water depends on novel material and process innovations. We present progress on
the development of a comprehensive thermodynamic model aimed to support heat
and mass balance calculations and process simulation of desalination processes
with produced water. Based on the electrolyte Non-Random Two Liquid theory
(eNRTL) for electrolyte solutions [Song and Chen, Ind. Eng. Chem. Res. 2009, 48, 7788-7797], the model intends to
cover major ions of concern for produced water management: Na⁺, K⁺,
Mg²⁺, Ca²⁺, Ba²⁺, Sr²⁺, Cl^-,
HCO₃^- and SO₄^2- ions.
In the thermodynamic framework of eNRTL, the concentration dependency of the
solution nonideality is accounted for with two binary interaction parameters
for each of the water-electrolyte interaction pairs and the
electrolyte?electrolyte interaction pairs. The temperature dependency of the
binary interaction parameters is accounted for with a Gibbs-Helmholtz type
expression with three temperature coefficients representing excess Gibbs
energy, excess enthalpy, and excess heat capacity contributions. With the binary
parameters regressed from thermodynamic data of aqueous single electrolyte
binary systems and aqueous two electrolyte ternary systems, the model has been
shown to provide accurate calculations and reliable predictions for various
thermodynamic properties of quaternary and quinary systems examined thus far
for the aqueous Na⁺-K⁺-Mg²⁺-Ca²⁺-Cl^--SO₄^2-
hexary system with temperatures from 273.15 K to 473.15 K and concentrations up
to salt saturation.
The model is being extended to cover Ba²⁺, Sr²⁺ and HCO₃^-
ions and it should become an indispensable scientific tool in the development
of novel desalination processes for high
salinity produced water in oil and gas productions.