The CPA Equation of State and an Activity Coefficient Model for Accurate Molar Enthalpy Calculations of Mixtures with Carbon Dioxide and Water/Brine
Abstract
Thermodynamic property calculations of mixtures containing carbon dioxide (CO _{2}) and water, including brines, are essential in theoretical models of many natural and industrial processes. The properties of greatest practical interest are density, solubility, and enthalpy. Many models for density and solubility calculations have been presented in the literature, but there exists only one study, by Spycher and Pruess, that has compared theoretical molar enthalpy predictions with experimental data [1]. In this report, we recommend two different models for enthalpy calculations: the CPA equation of state by Li and Firoozabadi [2], and the CO _{2} activity coefficient model by Duan and Sun [3]. We show that the CPA equation of state, which has been demonstrated to provide good agreement with density and solubility data, also accurately calculates molar enthalpies of pure CO _{2}, pure water, and both CO _{2}rich and aqueous (H _{2}Orich) mixtures of the two species. It is applicable to a wider range of conditions than the Spycher and Pruess model. In aqueous sodium chloride (NaCl) mixtures, we show that Duan and Sun’s model yields accurate results for the partial molar enthalpy of CO _{2}. It can be combined with another model for the brine enthalpy to calculatemore »
 Authors:
 Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
 Publication Date:
 Research Org.:
 Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
 Sponsoring Org.:
 USDOE
 OSTI Identifier:
 1194030
 Report Number(s):
 LLNLTR672077
 DOE Contract Number:
 AC5207NA27344
 Resource Type:
 Technical Report
 Country of Publication:
 United States
 Language:
 English
 Subject:
 03 NATURAL GAS; 58 GEOSCIENCES; 15 GEOTHERMAL ENERGY; 37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; 02 PETROLEUM
Citation Formats
Myint, P. C., Hao, Y., and Firoozabadi, A.. The CPA Equation of State and an Activity Coefficient Model for Accurate Molar Enthalpy Calculations of Mixtures with Carbon Dioxide and Water/Brine. United States: N. p., 2015.
Web. doi:10.2172/1194030.
Myint, P. C., Hao, Y., & Firoozabadi, A.. The CPA Equation of State and an Activity Coefficient Model for Accurate Molar Enthalpy Calculations of Mixtures with Carbon Dioxide and Water/Brine. United States. doi:10.2172/1194030.
Myint, P. C., Hao, Y., and Firoozabadi, A.. 2015.
"The CPA Equation of State and an Activity Coefficient Model for Accurate Molar Enthalpy Calculations of Mixtures with Carbon Dioxide and Water/Brine". United States.
doi:10.2172/1194030. https://www.osti.gov/servlets/purl/1194030.
@article{osti_1194030,
title = {The CPA Equation of State and an Activity Coefficient Model for Accurate Molar Enthalpy Calculations of Mixtures with Carbon Dioxide and Water/Brine},
author = {Myint, P. C. and Hao, Y. and Firoozabadi, A.},
abstractNote = {Thermodynamic property calculations of mixtures containing carbon dioxide (CO2) and water, including brines, are essential in theoretical models of many natural and industrial processes. The properties of greatest practical interest are density, solubility, and enthalpy. Many models for density and solubility calculations have been presented in the literature, but there exists only one study, by Spycher and Pruess, that has compared theoretical molar enthalpy predictions with experimental data [1]. In this report, we recommend two different models for enthalpy calculations: the CPA equation of state by Li and Firoozabadi [2], and the CO2 activity coefficient model by Duan and Sun [3]. We show that the CPA equation of state, which has been demonstrated to provide good agreement with density and solubility data, also accurately calculates molar enthalpies of pure CO2, pure water, and both CO2rich and aqueous (H2Orich) mixtures of the two species. It is applicable to a wider range of conditions than the Spycher and Pruess model. In aqueous sodium chloride (NaCl) mixtures, we show that Duan and Sun’s model yields accurate results for the partial molar enthalpy of CO2. It can be combined with another model for the brine enthalpy to calculate the molar enthalpy of H2OCO2NaCl mixtures. We conclude by explaining how the CPA equation of state may be modified to further improve agreement with experiments. This generalized CPA is the basis of our future work on this topic.},
doi = {10.2172/1194030},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2015,
month = 3
}

An equationofstate package for watercarbon dioxide mixtures has been constructed from available thermodynamic data that covers the range of interest to the Baca reservoir system. The package has been used to examine the thermodynamic state of the Baca reservoir fluid for conditions of temperature, pressure and CO/sub 2/ content believed to bracket conditions existing at the production depth of the wells in the Redondo Creek area. It is shown that the reservoir fluid may be either allliquid or twophase at various well locations and depths, depending on the CO/sub 2/ content. It is also shown that the CO/sub 2/ contentmore »

Equation of state mixing rule for nonideal mixtures using available activity coefficient model parameters and that allows extrapolation over large ran
In this paper, the authors demonstrate that a new mixing rule allows cubic equations of state to be used for a broad range of nonideal mixtures which previously could only be described by activity coefficient models. Further, the authors show that there is no need to recorrelate phase equilibrium data to do this; activity coefficient model parameters currently reported, for example in the DECHEMA Data Series, can be used directly in our model. Perhaps most important is that the authors also find that the authors can use the parameters in our model obtained from one low pressurelow temperature isotherm tomore » 
ReducedOrder Model for the Geochemical Impacts of Carbon Dioxide, Brine and Trace Metal Leakage into an Unconfined, Oxidizing Carbonate Aquifer, Version 2.1
The National Risk Assessment Partnership (NRAP) consists of 5 U.S DOE national laboratories collaborating to develop a framework for predicting the risks associated with carbon sequestration. The approach taken by NRAP is to divide the system into components, including injection target reservoirs, wellbores, natural pathways including faults and fractures, groundwater and the atmosphere. Next, develop a detailed, physics and chemistrybased model of each component. Using the results of the detailed models, develop efficient, simplified models, termed reduced order models (ROM) for each component. Finally, integrate the component ROMs into a system model that calculates risk profiles for the site. Thismore »